Dev Psych Ch 2 PDF

for more ebook/ testbank/ solution manuals requests: email [email protected] Chapter 2 Kateryna Kon/123RF The Start of Life: Prenatal Development Learning Objectives LO 2.1 Describe how genes and chromosomes provide our basic genetic endowment. LO 2.2 Compare monozygotic twins with dizygotic twins. L...

for more ebook/ testbank/ solution manuals requests: email [email protected] Chapter 2 Kateryna Kon/123RF The Start of Life: Prenatal Development Learning Objectives LO 2.1 Describe how genes and chromosomes provide our basic genetic endowment. LO 2.2 Compare monozygotic twins with dizygotic twins. LO 2.3 Describe how the sex of a child is determined. LO 2.4 Explain the mechanisms by which genes transmit information. LO 2.5 Describe the field of behavioral genetics. LO 2.6 Describe the major inherited disorders produced by damaged or mutated genes. LO 2.7 Describe the role of genetic counselors and differentiate between different forms of prenatal testing. LO 2.8 Explain how the environment and genetics work together to determine human characteristics. LO 2.9 Summarize how researchers study the interaction of genetic and environmental factors in development. LO 2.10 Explain how genetics and the environment jointly influence physical traits, intelligence, and personality. LO 2.11 Explain the role genetics and the environment play in the development of psychological disorders. LO 2.12 Describe ways in which genes influence the environment. 47 48 PART 1 Beginnings LO 2.13 Explain the process of fertilization. LO 2.14 Summarize the three stages of prenatal development. LO 2.15 Describe the challenges that relate to pregnancy. LO 2.16 Describe the threats to the fetal environ- ment and what can be done about them. Chapter Overview Earliest Development Genes and Chromosomes: The Code of Life Multiple Births: Two—or More—for the Genetic Price of One Male or Female? Establishing the Sex of the Child The Basics of Genetics: The Mixing and Matching of Traits The Human Genome and Behavioral Genetics: Cracking the Genetic Code Studying Development: How Much Is Nature? How Much Is Nurture? Genetics and the Environment: Working Together Psychological Disorders: The Role of Genetics and Environment Can Genes Influence the Environment? Prenatal Growth and Change Fertilization: The Moment of Conception Inherited and Genetic Disorders: When Development Deviates from the Norm The Stages of the Prenatal Period: The Onset of Development Genetic Counseling: Predicting the Future from the Genes of the Present Pregnancy Problems The Prenatal Environment: Threats to Development The Interaction of Heredity and Environments The Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes Prologue: Going with the Odds When a prenatal ultrasound at 20 weeks revealed that Tim and Laura Chen’s unborn son had a severe form of spina bifida, a condition in which a baby’s spine and spinal cord don’t develop properly, their first question was: Can this be fixed? Laura’s doctor outlined their choices. They could wait to enclose the spinal cord until after the baby’s birth, but this might endanger the spine and brain, which can be damaged in late pregnancy. And their child could still experience paralysis, cognitive impairments, and bladder and bowel issues. On the other hand, surgery could be performed before birth. Doctors would tip Laura’s uterus outside her body, make an incision, and sew up the hole exposing the spinal cord. There would be a greater risk of preterm labor, but a better chance of minimizing lifelong damage. The Chens chose fetal surgery. Three years later, their son has minor bladder issues, but he walks independently and his preschool cognitive assessment placed him in the 85th percentile. “We’re so lucky to be living in a time when such surgery is possible,” Laura says. Desizned/Shutterstock Looking Ahead Prenatal tests have become increasingly sophisticated. The Chens’ story illustrates the powerful benefits—and the often difficult decisions—that advances in our understanding of the prenatal period and our ability to detect physical problems prenatally have brought us. In this chapter, we’ll examine what developmental researchers and other scientists have learned about ways that heredity and the environment work in tandem to create and shape human beings and how that for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development 49 knowledge is being used to improve people’s lives. We begin with the basics of heredity, the genetic transmission of characteristics from biological parents to their children, by examining how we receive our genetic endowment. We’ll consider an area of study, behavioral genetics, that specializes in the consequences of heredity on behavior. We’ll also discuss what happens when genetic factors cause development to go off track and how such problems are dealt with through genetic counseling and, in some cases, manipulation of a child’s genes. But genes are only one part of the story of prenatal development. We’ll also consider the ways in which a child’s genetic heritage interacts with the environment in which they grow up—how one’s family, socioeconomic status, and life events can affect a variety of characteristics, including physical traits, intelligence, and even personality. Finally, we’ll focus on the first stage of development, tracing prenatal growth and change. We’ll review some of the alternatives available to couples who have difficulties conceiving. We’ll also talk about the stages of the prenatal period and how the prenatal environment offers both threats to—and the promise of—future growth. zygote Earliest Development We humans begin the course of our lives simply. Like individuals from thousands of other species, we start as a single cell, a tiny speck probably weighing no more than a 20-millionth of an ounce. But as we’ll see in this section, from this humble beginning, in a matter of just several months, if all goes well, a living, breathing individual infant is born. Genes and Chromosomes: The Code of Life LO 2.1 Describe how genes and chromosomes provide our basic genetic endowment. The single cell we described previously is created when a male reproductive cell, a sperm, pushes through the membrane of an ovum, a female reproductive cell. These gametes, as the male and female reproductive cells also are known, each contain huge amounts of genetic information. About an hour or so after the sperm enters the ovum, the two gametes suddenly fuse, becoming one cell, a zygote. The resulting combination of their genetic instructions—more than 2 billion chemically coded messages—is sufficient to begin creating a whole person. The blueprints for creating a person are stored and communicated in our genes, the basic units of genetic information. The roughly 25,000 human genes are the biological equivalent of “software” that programs the future development of all parts of the body’s “hardware.” All genes are composed of specific sequences of DNA (deoxyribonucleic acid) molecules. The genes are arranged in specific locations and in a specific order along 46 chromosomes, rod-shaped portions of DNA that are organized in 23 pairs. Only sex cells—the ova and the sperm—contain half this number, so that a child’s mother and father each provide one of the two chromosomes in each of the 23 pairs. The 46 chromosomes (in 23 pairs) in the new zygote contain the genetic blueprint that will guide cell activity for the rest of the individual’s life (Pennisi, 2000; International Human Genome Sequencing Consortium, 2001; see Figure 2-1). Through a process called mitosis, which accounts for the replication of most types of cells, nearly all the cells of the body will contain the same 46 chromosomes as the zygote. Specific genes in precise locations on the chain of chromosomes determine the nature and function of every cell in the body. For instance, genes determine which cells will ultimately become part of the heart and which will become part of the muscles of the leg. Genes also establish how different parts of the body will function—how rapidly the heart will beat, for example, or how much strength a muscle will have. the new cell formed by the process of fertilization genes the basic units of genetic information DNA (deoxyribonucleic acid) molecules the substance that genes are composed of, which determines the nature of every cell in the body and how it will function chromosomes rod-shaped portions of DNA that are organized in 23 pairs Figure 2-1 The Contents of a Single Human Cell At the moment of conception, humans receive about 25,000 genes, contained on 46 chromosomes in 23 pairs. About 25,000 Genes = 46 Chromosomes = 23 Chromosome Pairs = One Human Cell 50 PART 1 Beginnings CNRI/Science Source If each parent provides just 23 chromosomes, where does the potential for the vast diversity of human beings come from? The answer resides primarily in the nature of the processes that underlie the cell division of the gametes. When gametes—the sex cells, sperm and ova—are formed in the adult human body in a process called meiosis, each gamete receives one of the two chromosomes that make up each of the 23 pairs. Because for each of the 23 pairs it is largely a matter of chance which member of the pair is contributed, there are some 8 million different combinations possible. Furthermore, other processes, such as random transformations of particular genes, add to the variability of the genetic brew. The ultimate outcome: trillions of possible genetic combinations. With so many possible genetic mixtures provided by heredity, there is no likelihood that someday you’ll bump into a genetic duplicate of yourself—with one exception: an identical twin. At the moment of conception, humans receive 23 pairs of chromosomes, half from the mother and half from the father. These chromosomes contain thousands of genes. monozygotic twins twins who are genetically identical dizygotic twins twins who are produced when two separate ova are fertilized by two separate sperm at roughly the same time Multiple Births: Two—or More—for the Genetic Price of One LO 2.2 Compare monozygotic twins with dizygotic twins. Although it doesn’t seem surprising when dogs and cats give birth to several offspring at one time, in humans, multiple births are cause for comment. They should be: Less than 3 percent of all pregnancies produce twins, and the odds are even slimmer for triplets or higher-order multiples. Why do multiple births occur? Some occur when a cluster of cells in the ovum split off within the first 2 weeks after fertilization. The result is two genetically identical zygotes, which, because they come from the same original zygote, are called monozygotic. Monozygotic twins are twins who are genetically identical. Any differences in their future development can be attributed only to environmental factors because genetically they are exactly the same. However, multiple births are more commonly the result of two separate sperm fertilizing different ova, producing what are called dizygotic twins. Dizygotic twins are produced when two separate ova are fertilized by two separate sperm at roughly the same time. Because they are the result of two separate ovum–sperm combinations, they are no more genetically similar than two siblings born at different times. Of course, not all multiple births produce only two babies. Triplets, quadruplets, and even higher-order multiples are produced by either (or both) of the mechanisms that yield twins. Although the chances of having a multiple birth are typically slim, the odds rise considerably when fertility drugs are used before conception. Older women, too, are more likely to have multiple births, and multiple births are also more common in some families than in others. The increased use of fertility drugs and the rising average age of mothers giving birth led to a dramatic increase in multiple births in the 1980s and 1990s. However, that trend is declining (see Figure 2-2). Experts believe the reduction in multiple births is explained by the decline of the use of fertility therapies that involve the transfer of multiple embryos. (Martin et al., 2005; Hauser, 2019; Mbarek et al., 2019). There are also racial and national differences in the rate of multiple births, probably due to inherited differences in the likelihood that more than one ovum will be released at a time. One out of 70 Black American couples have dizygotic births, compared with 1 out of 86 for white American couples. Furthermore, in some areas of central Africa, the rate of dizygotic births is among the highest in the world (Choi, 2017; Martin & Osterman, 2019). Mothers carrying multiple children run a higher-than-average risk of premature delivery and birth complications. Consequently, these mothers must be particularly concerned about their prenatal care. for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development 51 Figure 2-2 Rising Multiples The number and rate of twin births has risen considerably over the past 3 decades. 160,000 40 140,000 35 30 Rate 100,000 25 80,000 20 Number 60,000 15 2019 2017 2015 2013 2011 2009 2007 2005 2003 2001 1999 1997 1995 1993 0 1991 0 1989 5 1987 20,000 1985 10 1983 40,000 Rate of Births 120,000 1981 Number of Births (Source: Martin & Osterman, 2019 and Martin et al, 2021.) Figure 2-3 Determining Sex Male or Female? Establishing the Sex of the Child LO 2.3 Describe how the sex of a child is determined. Recall that there are 23 matched pairs of chromosomes. In 22 of these pairs, each chromosome is similar to the other member of its pair. The one exception is the 23rd pair, which is the one that determines the sex of the child. In females, the 23rd pair consists of two matching, relatively large, X-shaped chromosomes, appropriately identified as XX. In males, however, the members of the pair are dissimilar. One consists of an X-shaped chromosome, but the other is a shorter, smaller, Y-shaped chromosome. This pair is identified as XY. As we discussed previously, each gamete carries one chromosome from each of the parent’s 23 pairs of chromosomes. Because a female’s 23rd pair of chromosomes are both Xs, an ovum will always carry an X chromosome, no matter which chromosome of the 23rd pair it gets. A male’s 23rd pair is XY, so each sperm could carry either an X or a Y chromosome. If the sperm contributes an X chromosome when it meets an ovum (which, remember, will always contribute an X chromosome), the child will have an XX pairing on the 23rd chromosome—a female. If the sperm contributes a Y chromosome, the result will be an XY pairing—a male (see Figure 2-3). It is clear from this process that the father’s sperm determines the sex of the child. This fact is leading to the development of techniques that will allow parents to increase the chances of specifying the sex of their child. For example, one technique uses a fluorescent dye to distinguish sperm carrying X and Y chromosomes, whereas another makes use of the higher mass of X chromosomes to identify sperm of a particular type by using a kind of chemical filter. Once the desired type of sperm are identified, they are used to impregnate the mother. Neither is anywhere near foolproof (Kudina, 2019). Of course, procedures for choosing a child’s sex raise ethical and practical issues. For example, in cultures that value one sex over the other, might there be a kind of sex discrimination prior to birth? Furthermore, a shortage of children of the less preferred sex might ultimately emerge. Many questions remain, then, before sex selection becomes routine (Sharma, 2008; Bhagat et al., 2012; Kaur & Kapoor, 2021). When an ovum and a sperm meet at the moment of fertilization, the ovum is certain to provide an X chromosome, whereas the sperm will provide either an X or a Y chromosome. If the sperm contributes its X chromosome, the child will have an XX pairing on the 23rd chromosome—a female. If the sperm contributes a Y chromosome, the result will be an XY pairing—a male. Does this mean that females are more likely to be conceived than males? Female Male X & X X & Y The 23rd pair of chromosomes of the ovum consists of chromosomes X&X The 23rd pair of chromosomes of the sperm consists of chromosomes X&Y X & X X & Y Baby girl Baby boy 52 PART 1 Beginnings The Basics of Genetics: The Mixing and Matching of Traits LO 2.4 dominant trait the one trait that is expressed when two competing traits are present recessive trait a trait within an organism that is present but is not expressed genotype the underlying combination of genetic material present (but not outwardly visible) in an organism phenotype an observable trait; the trait that is actually seen homozygous similar genes inherited from parents for a given trait heterozygous different forms of a gene inherited from parents for a given trait Explain the mechanisms by which genes transmit information. What determined the color of your hair? Why are you tall or short? What made you susceptible to hay fever? And why do you have so many freckles? To answer these questions, we need to consider the basic mechanisms involved in the way that the genes we inherit from our parents transmit information. We can start by examining the discoveries of an Austrian monk, Gregor Mendel (1822–1884), in the mid-1800s. In a series of simple yet convincing experiments, Mendel cross-pollinated pea plants that always produced yellow seeds with pea plants that always produced green seeds. The result was not, as one might guess, a plant with a combination of yellow and green seeds. Instead, all of the resulting plants had yellow seeds. At first it appeared that the green-seeded plants had had no influence. However, Mendel’s additional research proved this was not true. He bred together plants from the new, yellow-seeded generation that had resulted from his original cross-breeding of the green-seeded and yellow-seeded plants. The consistent result was a ratio of three-fourths yellow seeds to one-fourth green seeds. Why did this ratio of yellow to green seeds appear so consistently? It took Mendel’s genius to provide an answer. Based on his experiments with pea plants, he argued that when two competing traits, such as a green or yellow coloring of seeds, were both present, only one could be expressed. The one that was expressed was called a dominant trait. Meanwhile, the other trait remained present in the organism, although it was not expressed (displayed). This was called a recessive trait. In the case of Mendel’s original pea plants, the offspring plants received genetic information from both the green-seeded and yellow-seeded parents. However, the yellow trait was dominant, and consequently the recessive green trait did not assert itself. Keep in mind, however, that genetic material relating to both parent plants is present in the offspring, even though it cannot be seen. The genetic information is known as the organism’s genotype. A genotype is the underlying combination of genetic material present (but outwardly invisible) in an organism. In contrast, a phenotype is the observable trait, the trait that is actually seen. Although the offspring of the yellow-seeded and green-seeded pea plants all have yellow seeds (i.e., they have a yellow-seeded phenotype), the genotype consists of genetic information relating to both parents. And what is the nature of the information in the genotype? To answer that question, let’s turn from peas to people. In fact, the principles are the same not just for plants and humans but for the majority of species. Recall that parents transmit genetic information to their offspring via the chromosomes they contribute through the gamete they provide during fertilization. Some of the genes form pairs called alleles, genes governing traits that may take alternate forms, such as hair or eye color. For example, brown eye color is a dominant trait (B); blue eyes are recessive (b). A child’s allele may contain similar or dissimilar genes from each parent. If, on the one hand, the child receives similar genes, they are said to be homozygous for the trait. On the other hand, if the child receives different forms of the gene from its parents, they are said to be heterozygous. In the case of heterozygous alleles (Bb), the dominant characteristic, brown eyes, is expressed. However, if the child happens to receive a recessive allele from each of its parents and, therefore, lacks a dominant characteristic (bb), they will display the recessive characteristic, such as blue eyes. EXAMPLE OF TRANSMISSION OF GENETIC INFORMATION. We can see this process at work in humans by considering the transmission of phenylketonuria (PKU), an inherited disorder in which a child is unable to make use of phenylalanine, an essential amino acid present in proteins found in milk and other foods. If left untreated, PKU for more ebook/ testbank/ solution manuals requests: allows phenylalanine to build up to toxic levels, causing brain damage and intellectual disabilities (Widaman, 2009; Palermo et al., 2017; Jaulent et al., 2020). PKU is produced by a single allele, or pair of genes. As shown in Figure 2-4, we can label each gene of the pair with a P if it carries a dominant gene, which causes the normal production of phenylalanine, or a p if it carries the recessive gene that produces PKU. In cases in which neither parent is a PKU carrier, both the mother’s and the father’s pairs of genes are the dominant form, symbolized as PP (Figure 2-4a). Consequently, no matter which member of the pair is contributed by the mother and father, the resulting pair of genes in the child will be PP, and the child will not have PKU. Consider, however, what happens if one of the parents has a recessive p gene. In this case, which we can symbolize as Pp, the parent will not have PKU because the normal P gene is dominant. But the recessive gene can be passed down to the child (Figure 2-4b). This is not so bad: If the child has only one recessive gene, it will not suffer from PKU. But what if both parents carry a recessive p gene (Figure 2-4c)? In this case, although neither parent has the disorder, it is possible for the child to receive a recessive gene from both parents. The child’s genotype for PKU then will be pp, and they will have the disorder. Remember, though, that even children whose parents both have the recessive gene for PKU have only a 25 percent chance of inheriting the disorder. Due to the laws of probability, 25 percent of children with Pp parents will receive the dominant gene from each parent (these children’s genotype would be PP) and 50 percent will receive the dominant gene from one parent and the recessive gene from the other (their genotypes would be either Pp or pP). Only the unlucky 25 percent who receive the recessive gene from each parent and end up with the genotype pp will suffer from PKU. email Chapter 2 [email protected] The Start of Life: Prenatal Development Figure 2-4 PKU Probabilities Phenylketonuria (PKU), a disease that causes brain damage and intellectual disabilities, is produced by a single pair of genes inherited from one’s mother and father. (a) If neither parent carries a gene for the disease, a child cannot develop PKU. (b) Even if one parent carries the recessive gene but the other doesn’t, the child cannot inherit the disease. (c) However, if both parents carry the recessive gene, there is a one in four chance that the child will have PKU. a Mother Father Mother Father contributes either contributes either P or P P or P P P P P PP PP PP PP Normal Normal Normal Normal Result: No child can inherit PKU Does not carry Does not carry recessive recessive PKU gene PKU gene b Mother P p Father P P Mother Father contributes either contributes either P or p P or P PP PP Normal Normal Carries recessive Does not carry recessive PKU gene PKU gene c Mother Father The transmission of PKU is a good way of illustrating the basic principles of how P P genetic information passes from parent to child, p p although the case of PKU is simpler than most cases of genetic transmission. Relatively few traits are governed by a single pair of genes. Instead, most traits are the result of polygenic inheritance. In polygenic inheritance, a combination of multiple gene pairs is responsi- Carries recessive Carries recessive PKU gene PKU gene ble for the production of a particular trait. Furthermore, some genes come in several alternate forms, and still others act to modify the way that particular genetic traits (produced by other alleles) are displayed. Genes also vary in terms of their reaction range, the potential degree of variability in the actual expression of a trait due to environmental conditions. And some traits, such as blood type, are produced by genes in which neither member of a pair of genes can be classified as purely dominant or recessive. Instead, the trait is expressed in terms of a combination of the two genes—such as type AB blood. POLYGENIC TRAITS. 53 pP Carrier pP Carrier Result: No child will be afflicted with PKU, although two in four will carry the recessive gene Mother Father contributes either contributes either P or p P or p PP Pp pP pp Normal Carrier Carrier Afflicted with PKU Result: One in four children will inherit two dominant genes and will not have PKU; two in four will inherit one recessive gene and not be afflicted with PKU but will carry the recessive gene; and one in four will have PKU polygenic inheritance inheritance in which a combination of multiple gene pairs is responsible for the production of a particular trait 54 PART 1 Beginnings Figure 2-5 Inheriting Hemophilia Hemophilia, a blood-clotting disorder, has been an inherited disorder throughout the royal families of Europe, as illustrated by the descendants of Queen Victoria of Great Britain. (Source: Kimball, John W., Biology, 5th Ed., © 1983. Reprinted and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.) Queen Victoria Prince Albert Normal female h H h Edward Victoria VII Alice h George V George VI Henry of Prussia Alfred H H Waldemar of Prussia (lived to 56) Henry (died at 4) Arthur h h Alice H Hemophilic male h Henry H Victoria Alfonso Eugenie Leopold Maurice H H Mary Czarevitch Viscount Alexis Trematon (murdered) (died at 20) H Helena Beatrice Leopold Alexandra H Irene Frederick William (died at 3) Carrier female Normal male died in infancy Alfonso Gonzalo (bled to death after accidents) no hemophilia in present British royal family X-linked genes genes that are considered recessive and are located only on the X chromosome A number of recessive genes, called X-linked genes, are located only on the X chromosome. Recall that in females, the 23rd pair of chromosomes is an XX pair, and in males it is an XY pair. One result is that males have a higher risk for a variety of X-linked disorders because males lack a second X chromosome that can counteract the genetic information that produces the disorder. For example, males are significantly more apt to have red–green color blindness, a disorder produced by a set of genes on the X chromosome. Similarly, hemophilia, a blood-clotting disorder, is produced by X-linked genes. Hemophilia has been a recurrent problem in the royal families of Europe, as illustrated in Figure 2-5, which shows the inheritance of hemophilia in the descendants of Queen Victoria of Great Britain. The Human Genome and Behavioral Genetics: Cracking the Genetic Code LO 2.5 behavioral genetics the study of the effects of heredity on behavior and psychological characteristics Describe the field of behavioral genetics. Mendel’s achievements in recognizing the basics of genetic transmission of traits were trailblazing. However, they mark only the beginning of our understanding of how those particular characteristics are passed on from one generation to the next. The most recent milestone in understanding genetics was reached in early 2001, when molecular geneticists succeeded in mapping the specific sequence of genes on each chromosome. This accomplishment stands as one of the most important moments in the history of genetics, and, for that matter, all of biology (International Human Genome Sequencing Consortium, 2001). Already, the mapping of the gene sequence has provided important advances in our understanding of genetics. For instance, the number of human genes, long thought to be 100,000, has been revised downward to 25,000—not many more than for organisms that are far less complex than the human (see Figure 2-6). Furthermore, scientists have discovered that all humans share 99.9 percent of the gene sequence. What this means is that we humans are far more similar to one another than we are different. It also indicates that many of the differences that seemingly separate people—such as race—are, literally, only skin-deep. The mapping of the human genome will also help identify particular disorders to which a given individual is susceptible (Goldman & Domschke, 2014; Biesecker & Peay, 2013; Lister Hill National Center for Biomedical Communications, 2020). The mapping of the human gene sequence supports the field of behavioral genetics. As the name implies, behavioral genetics studies the effects of heredity on behavior and for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development Figure 2-6 Uniquely Human? Humans have about 25,000 genes, making them not much more genetically complex than fruit flies and less genetically complex than trees, apples, and wheat. Approximate Number of Genes 120,000 107,000 100,000 80,000 57,000 60,000 45,000 40,000 25,000 20,000 14,000 182 0 Fruit Fly Human Wheat Apple Carsonella ruddii (bacterium) Tree psychological characteristics. Rather than simply examining stable, unchanging characteristics such as hair or eye color, behavioral genetics takes a broader approach, considering how our personality and behavioral habits are affected by genetic factors (Li, 2003; Judge et al., 2012; Krüger et al., 2017; Harden, 2021). Personality traits such as shyness or sociability, moodiness, and assertiveness are among the areas being studied. Other behavior geneticists study psychological disorders, such as major depressive disorder, attention-deficit/hyperactivity disorder, and schizophrenia spectrum disorder, looking for possible genetic links (Haeffel et al., 2008; Wang et al., 2012; Plomin et al., 2016; Smeland et al., 2020; see Table 2-1). Behavioral genetics holds substantial promise. For one thing, researchers working within the field have gained a better understanding of the specifics of the genetic code that underlies human behavior and development. Even more important, researchers are seeking to identify how genetic defects may be remedied (Peltonen & McKusick, 2001; Bleidorn et al., 2014). To understand how a remedial possibility might come about, we need to consider the ways in which genetic factors, which normally cause development to proceed so smoothly, may falter. Table 2-1 The Genetic Basis of Selected Disorders Disorder Current Ideas of Genetic Basis Huntington disease Mutations in the HTT gene. Early onset (familial) Alzheimer disease Three distinct genes identified: APP, PSEN1, or PSEN2, which produce toxic protein fragments called amyloid beta peptide. Fragile X syndrome Mutations in the FMR1 gene. Attention-deficit/hyperactivity disorder (ADHD) Evidence in some studies has linked ADHD with the dopamine D4 and D5 genes, but the complexity of the disease makes it difficult to identify a specific gene beyond reasonable doubt. Alcoholism Research suggests that genes that affect the activity of neurotransmitters serotonin and GABA likely are involved in the risk for alcoholism. Schizophrenia There are more than 100 genes that have been associated with schizophrenia, but DRD2 appears to be of particular importance. (Source: Based on McGuffin et al., 2001; Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014; U.S. National Library of Medicine, 2020.) 55 56 PART 1 Beginnings Inherited and Genetic Disorders: When Development Deviates from the Norm LO 2.6 Describe the major inherited disorders produced by damaged or mutated genes. PKU is just one of several disorders that may be inherited. Like a bomb that is harmless until its fuse is lit, a recessive gene responsible for a disorder may be passed on unknowingly from one generation to the next, revealing itself only when, by chance, it is paired with another recessive gene. It is only when two recessive genes come together like a match and a fuse that the gene will express itself and a child will inherit the genetic disorder. But there is another way that genes are a source of concern: In some cases, genes become physically damaged. For instance, genes may break down due to wear and tear or chance events occurring during the cell division processes of meiosis and mitosis. Sometimes genes, for no known reason, spontaneously change their form, a process called spontaneous mutation. Alternatively, certain environmental factors, such as exposure to X-rays or even highly polluted air, may produce a malformation of genetic material (see Figure 2-7). When such damaged genes are passed on to a child, the results can be disastrous in terms of future physical and cognitive development (Acheva et al., 2014; Cuny et al., 2020). In addition to PKU, which occurs once in 10,000 to 20,000 births, other inherited and genetic disorders include: Down syndrome a disorder produced by the presence of an extra chromosome on the 21st pair; once referred to as mongolism Down syndrome. As noted previously, most people have 46 chromosomes, arranged in 23 pairs. One exception is individuals with Down syndrome, a disorder produced by the presence of an extra chromosome on the 21st pair. Down syndrome is the most Figure 2-7 Inhaled Air and Genetic Mutations Inhalation of unhealthy, polluted air may lead to mutations in genetic material in sperm. These mutations may be passed on, damaging the fetus and affecting future generations. (Source: Based on Samet et al., 2004, p. 971.) Genetic material mutation Sperm email Chapter 2 [email protected] The Start of Life: Prenatal Development frequent cause of intellectual disabilities. It occurs in about 1 out of 700 births, although the risk is much greater in mothers who are unusually young or old (Channell et al., 2014; Glasson et al., 2016; Correa-de-Araujo & Yoon, 2021). Fragile X syndrome. Fragile X syndrome occurs when a particular gene is injured on the X chromosome. The result is mild to moderate intellectual disability (Hocking et al., 2012; Shelton et al., 2017; Fitzpatrick et al., 2020). Sickle-cell anemia. Around 10 percent of people of African descent carry genes that produce sickle-cell anemia, and 1 in 365 actually experiences the disease. Sickle-cell anemia is a blood disorder that gets its name from the shape of the red blood cells in those who have it. Symptoms include poor appetite, stunted growth, a swollen stomach, and yellowish eyes. People afflicted with the most severe form of the disease rarely live beyond childhood. However, for those with less severe cases, medical advances have produced significant increases in life expectancy (Vacca & Blank, 2017; Piccin et al., 2019; Centers for Disease Control and Prevention [CDC], 2021). 57 fragile X syndrome a disorder produced by injury to a gene on the X chromosome, producing mild to moderate intellectual disability sickle-cell anemia a blood disorder that gets its name from the shape of the red blood cells in those who have it Tay-Sachs disease. Occurring mainly in Jews of Eastern European ancestry and in French-Canadians, Tay-Sachs disease usually causes death before its victims reach school age. There is no treatment for the disorder, which produces blindness and muscle degeneration prior to death. Sickle-cell anemia, named for the pres Klinefelter syndrome. One male out of every 500 is born with Klinefelter syndrome, the ence of misshapen red blood cells, is presence of an extra X chromosome. The resulting XXY complement produces underde- carried in the genes of 1 in 10 Blacks. veloped genitals, extreme height, and enlarged breasts. Klinefelter syndrome is one of a number of genetic abnormalities that result from receiving the improper number of sex Tay-Sachs disease chromosomes. For instance, there are disorders produced by an extra Y chromosome a disorder that produces blindness (XYY), a missing second chromosome (X0, called Turner syndrome), and three X chromo- and muscle degeneration prior to somes (XXX). Such disorders are typically characterized by problems relating to sexual death; there is no treatment characteristics and by intellectual deficits (Turriff et al., 2016; Zhang et al., 2020; Martin Klinefelter syndrome et al., 2021). Intersex. Previously called hermaphroditism, an intersex person is born with a rare combination of chromosomes, gene patterns, and sexual organ configurations. Sometimes an intersex infant has both male and female sex organs, or their sex organs are ambiguous. Intersex occurs in only 1 in 4,500 births (Ernst et al., 2018). It is important to keep in mind that the mere fact that a disorder has genetic roots does not mean that environmental factors do not also play a role. Consider, for instance, sickle-cell anemia, which primarily afflicts people of African descent. Because the disease can be fatal in childhood, we’d expect that those who suffer from it would be unlikely to live long enough to pass it on. This does seem to be true, at least in the United States: Compared with parts of West Africa, the incidence in the United States is much lower. But why shouldn’t the incidence of sickle-cell anemia also be gradually reduced for people in West Africa? This question proved puzzling for many years, until scientists determined that carrying the sickle-cell gene raises immunity to malaria, which is a common disease in West Africa. This heightened immunity meant that people with the sickle-cell gene had a genetic advantage (in terms of resistance to malaria) that offset, to some degree, the disadvantage of being a carrier of the sickle-cell gene. The lesson of sickle-cell anemia is that genetic factors are intertwined with environmental considerations and can’t be looked at in isolation. Furthermore, we need to remember that although we’ve been focusing on inherited factors that can go awry, in the vast majority of cases the genetic mechanisms with which we are endowed work quite well. Overall, 95 percent of children born in the United States are healthy and normal. For the some 250,000 who are born each year with some sort of physical or mental disorder, appropriate intervention often can help treat and, in some cases, cure the problem. Moreover, due to advances in behavioral genetics, genetic difficulties increasingly can be forecast, anticipated, and planned for before a child’s birth, enabling parents to a disorder resulting from the presence of an extra X chromosome that produces underdeveloped genitals, extreme height, and enlarged breasts Bill Longcore/ScienceSource for more ebook/ testbank/ solution manuals requests: 58 PART 1 Beginnings take steps before the child is born to reduce the severity of certain genetic conditions. In fact, as scientists’ knowledge regarding the specific location of particular genes expands, predictions of what the genetic future may hold are becoming increasingly exact, as we discuss next (Crombag et al., 2020). Genetic Counseling: Predicting the Future from the Genes of the Present LO 2.7 genetic counseling the discipline that focuses on helping people deal with issues relating to inherited disorders Describe the role of genetic counselors and differentiate between different forms of prenatal testing. If you knew that your mother and grandmother had died of Huntington disease—a devastating, always fatal inherited disorder marked by tremors and intellectual deterioration—to whom could you turn to learn your own chances of developing the disease? The best person to turn to would be a member of a field that, just a few decades ago, was nonexistent: genetic counseling. Genetic counseling focuses on helping people deal with issues relating to inherited disorders. Genetic counselors use a variety of data in their work. For instance, couples contemplating having a child may seek to determine the risks involved in a future pregnancy. In such a case, a counselor will take a thorough family history, seeking any familial incidence of birth defects that might indicate a pattern of recessive or X-linked genes. In addition, the counselor will take into account factors such as the age of the mother and father and any previous abnormalities in other children they may have already had (Lyon, 2012; O’Doherty, 2014; Austin, 2016; Madlensky et al., 2017; Keenan et al., 2020). Typically, genetic counselors suggest a thorough physical examination. Such an examination may identify physical abnormalities that potential parents may have and not be aware of. In addition, samples of blood, skin, and urine may be used to isolate and examine specific chromosomes. Possible genetic defects, such as the presence of an extra sex chromosome, can be identified by assembling a karyotype, a chart containing enlarged photos of each of the chromosomes. PRENATAL TESTING. A variety of techniques can be used to assess the health of an unborn child if a woman is already pregnant (see Table 2-2 for a list of currently available tests). The earliest test is a first-trimester screen, which combines a blood test and ultrasound Table 2-2 Fetal Development Monitoring Techniques Technique Description Amniocentesis Done between the 15th and 20th weeks of pregnancy, this procedure examines a sample of the amniotic fluid, which contains fetal cells. Recommended if either parent carries Tay-Sachs, spina bifida, sickle-cell, Down syndrome, muscular dystrophy, or Rh disease. Chorionic villus sampling (CVS) Done at 10 to 13 weeks, either transabdominally or transcervically, depending on where the placenta is located. Involves inserting a needle (abdominally) or a catheter (cervically) into the substance of the placenta but staying outside the amniotic sac and removing 10 to 15 milligrams of tissue for analysis. The technique identifies instances of Down syndrome and other problems. Embryoscopy Examines the embryo or fetus during the first 12 weeks of pregnancy by means of a fiberoptic endoscope inserted through the cervix. Can be performed as early as week 5. Access to the fetal circulation may be obtained through the instrument, and direct visualization of the embryo permits the diagnosis of malformations. Fetal blood sampling (FBS) Performed after 18 weeks of pregnancy by collecting a small amount of blood from the umbilical cord for testing. Used to detect Down syndrome and most other chromosome abnormalities in the fetuses of couples who are at increased risk of having an affected child. Many other diseases can be diagnosed using this technique. Sonoembryology Used to detect abnormalities in the first trimester of pregnancy. Involves high-frequency transvaginal probes and digital image processing. In combination with ultrasound, it can detect more than 80 percent of all malformations during the second trimester. Ultrasound (sonogram) Uses very high frequency sound waves to detect structural abnormalities or multiple pregnancies, measure fetal growth, judge gestational age, and evaluate uterine abnormalities. Also used as an adjunct to other procedures, such as amniocentesis. email Chapter 2 [email protected] The Start of Life: Prenatal Development 59 sonography in the 11th to 13th weeks of pregnancy and can identify chromosomal abnormalities and other disorders, such as heart problems. In ultrasound sonography, highfrequency sound waves scan the mother’s womb. These waves produce a rather indistinct, but useful, image of the unborn baby, whose size and shape can then be assessed. Repeated use of ultrasound sonography can reveal developmental patterns. Although the accuracy of blood tests and ultrasound in identifying abnormalities is not high early in pregnancy, it becomes more accurate later on. A more invasive test, chorionic villus sampling (CVS), can be employed if blood tests and ultrasound have identified a potential problem or if there is a family history of inherited disorders. CVS involves inserting a thin needle into the area surrounding the fetus and taking In amniocentesis, a sample of fetal cells is withdrawn from the amniotic small samples of hair-like material that surrounds the sac and used to identify a number of genetic defects. embryo. The test can be done between the 10th and 13th weeks of pregnancy. However, it produces a risk of misultrasound sonography carriage of 1 in 100 to 1 in 200. Because of the risk, its use is relatively infrequent. In amniocentesis, a small sample of fetal cells is drawn by a tiny needle inserted into a process in which high-frequency the amniotic fluid surrounding the unborn fetus. Carried out 15 to 20 weeks into the sound waves scan the mother’s pregnancy, amniocentesis allows analysis of the fetal cells that can identify a variety of womb to produce an image of genetic defects with nearly 100 percent accuracy. In addition, the sex of the child can be the unborn baby, whose size and determined. Although there is always a danger to the fetus in an invasive procedure such shape can then be assessed as amniocentesis, it is generally safe, with the risk of miscarriage 1 in 200 to 1 in 400. chorionic villus sampling (CVS) After the various tests are complete and all possible information is available, the a test used to find genetic defects couple will meet with the genetic counselor again. Typically, counselors avoid giving spethat involves taking samples of cific recommendations. Instead, they lay out the facts and present various options, ranghair-like material that surrounds ing from doing nothing to taking more drastic steps, such as terminating the pregnancy the embryo through abortion. Ultimately, the parents must decide what course of action to follow. The newest role of genetic counselors involves testing people to identify whether they themselves, rather than their children, are susceptible to future disorders because of genetic abnormalities. For instance, Huntington disease typically does not manifest until people reach their 40s. However, genetic testing can identify much earlier whether a person carries the flawed gene that produces Huntington disease. Presumably, people’s knowledge that they carry the gene can help them prepare for the future (Sánchez-Castañeda et al., 2015; Stopford et al., 2020). SCREENING FOR FUTURE PROBLEMS. From a Health Care Provider’s Perspective What are some ethical and philosophical questions that surround the issue of genetic counseling? Might it sometimes be unwise to know ahead of time about possible genetically linked disorders that might afflict your child or yourself? In addition to Huntington disease, more than a thousand disorders can be predicted on the basis of genetic testing (see Table 2-3). Although such testing may bring welcome relief from future worries if the results are negative, positive results may produce just the opposite effect. In fact, genetic testing raises difficult practical and ethical questions (Klitzman, 2012; Uhlmann & Roberts, 2018; Bordet et al., 2020; de Wert et al., 2021). Suppose, for instance, a woman who thought she was susceptible to Huntington disease was tested in her 20s and found that she did not carry the defective gene. Obviously, she would experience tremendous relief. But suppose she found that she did carry the flawed gene and was therefore going to get the disease. In this case, she might well experience depression or anger. In fact, some studies show that 10 percent of people who find amniocentesis the process of identifying genetic defects by examining a small sample of fetal cells drawn by a needle inserted into the amniotic fluid surrounding the fetus CHASSENET/BSIP SA/Alamy Stock Photo for more ebook/ testbank/ solution manuals requests: 60 PART 1 Beginnings Table 2-3 Disorders Identifiable Through DNA-Based Genetic Tests Disease Description Adult polycystic kidney disease Kidney failure and liver disease Alpha-1-antitrypsin deficiency Emphysema and liver disease Alzheimer disease Late-onset variety of senile dementia Amyotrophic lateral sclerosis (Lou Gehrig disease) Progressive motor function loss leading to paralysis and death Ataxia telangiectasia Progressive brain disorder resulting in loss of muscle control and cancers Breast and ovarian cancer (inherited) Early onset tumors in breasts and ovaries Charcot-Marie-Tooth Loss of feeling in ends of limbs Congenital adrenal hyperplasia Hormone deficiency; ambiguous genitalia and male pseudohermaphroditism Cystic fibrosis Thick mucus accumulations in lungs and chronic infections in lungs and pancreas Duchenne muscular dystrophy (Becker muscular dystrophy) Severe to mild muscle wasting, deterioration, weakness Down syndrome Mild to moderate intellectual disability Dystonia Muscle rigidity, repetitive twisting movements Factor V-Leiden Blood-clotting disorder Fanconi anemia Anemia, leukemia, skeletal deformities Fragile X syndrome Intellectual disability Gaucher disease Enlarged liver and spleen, bone degeneration Hemophilia A and B Bleeding disorders Hereditary nonpolyposis colon cancers Early onset tumors in colon and sometimes other organs Huntington disease Progressive neurological degeneration, usually beginning in midlife Myotonic dystrophy Progressive muscle weakness Neurofibromatosis, type 1 Multiple benign nervous system tumors that can be disfiguring; cancers Phenylketonuria Progressive intellectual disability due to missing enzyme; correctable by diet Prader Willi/Angelman syndromes Decreased motor skills, cognitive impairment, early death Sickle-cell disease Blood cell disorder; chronic pain and infections Spinal muscular atrophy Severe, usually lethal progressive muscle-wasting disorder in children Tay-Sachs disease Seizures, paralysis; fatal neurological disease of early childhood Thalassemias Anemias (Sources: Human Genome Project, 2010, http://www.ornl.gov/sci/techresources/Human_Genome/medicine/genetest.shtml; Genetics Home Reference, 2017, https://ghr.nlm.nih.gov/primer/testing/uses; Centers for Disease Control and Prevention [CDC], 2020a.) they have the flawed gene that leads to Huntington disease never recover fully on an emotional level (Hamilton, 1998; Myers, 2004; Wahlin, 2007). Genetic testing clearly is a complicated issue. It rarely provides a simple yes or no answer as to whether an individual will be susceptible to a disorder. Instead, typically it presents a range of probabilities. In some cases, the likelihood of actually becoming ill depends on the type of environmental stressors to which a person is exposed. Personal differences also affect a given person’s susceptibility to a disorder (Bonke et al., 2005; Lucassen, 2012; Crozier et al., 2015; Djurdjinovic & Peters, 2017). As our understanding of genetics continues to grow, researchers and medical practitioners have moved beyond testing and counseling to actively working to change flawed genes. The possibilities for genetic intervention and manipulation increasingly border on what once was science fiction—as we consider next. ARE “DESIGNER BABIES” IN OUR FUTURE? Adam Nash was born to save his older sister Molly’s life—literally. Molly was suffering from a rare disorder called Fanconi anemia, which meant that her bone marrow was failing to produce blood cells. This disease can have devastating effects on young children, for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development 61 including birth defects and certain cancers. Many don’t survive to adulthood. Molly’s best hope for overcoming this disease was to grow healthy bone marrow by receiving a transplant of immature blood cells from the placenta of a newborn sibling. But not just any sibling would do; it had to be one with compatible cells that would not be rejected by Molly’s immune system. So Molly’s parents turned to a new and risky technique that had the potential to save Molly by using cells from her unborn brother. Molly’s parents were the first to use a genetic screening technique called preimplantation genetic diagnosis (PGD) to ensure that their next child would be free of Fanconi anemia. With PGD, a newly fertilized embryo can be screened for a variety of genetic diseases before it is implanted in the mother’s uterus to develop. Doctors fertilized several of Molly’s mother’s eggs with her husband’s sperm in a test tube. They then examined the embryos to ensure that they would only implant the embryo that PGD revealed to be both genetically healthy and a match for Molly. When Adam was born 9 months later, Molly got a new lease on life, too: The transplant was a success, and Molly was cured of her disease. Molly’s parents and their doctors also opened a controversial new chapter in genetic engineering involving the use of advances in reproductive medicine that give parents a degree of prenatal control over the traits of their children. Another procedure that makes this level of genetic control possible is germ line therapy, in which cells are taken from an embryo and then replaced after the defective genes they contain have been repaired. Although PGD and germ line therapy have important uses in the prevention and treatment of serious genetic disorders, concerns have been raised over whether such scientific advances can lead to the development of “designer babies”—infants that have been genetically manipulated to have traits their parents wish for. The question is whether these procedures can and should be used not only to correct undesirable genetic defects but also to breed infants for specific purposes or to “improve” future generations on a genetic level—as we consider further in From Research to Practice. From Research to Practice The Promise of CRISPR: Can We Create Made-to-Order Babies? And Should We? What if science could devise a way to prevent viral diseases such as COVID-19 entirely by removing the cellular receptor sites that the viruses exploit? What if genetic engineering could give us a way to create infants that are completely resistant to measles, influenza, or HIV/AIDS? How about if we could just delete the genes responsible for genetic disorders such as cystic fibrosis or sickle-cell anemia and provide a normal life for infants who would have otherwise faced a shortened lifetime filled with pain and suffering? Wouldn’t that be a no-brainer, if we could? Although it may sound like the stuff of science fiction, the technology to achieve these amazing feats is real and exists now. It’s called CRISPR, an acronym that refers to the clustered repeated sequences in bacterial DNA that allows them to target and destroy attacking viruses. Scientists turned this natural bacterial ability into a tool that can edit DNA—an accomplishment that earned pioneers Emmanuelle Charpentier and Jennifer Doudna the 2020 Nobel Prize in chemistry. This tool is what offers humanity the potential to prevent and cure devastating infectious and genetic diseases—and indeed, it has already been used once to engineer a pair of twin infants who are incapable of contracting HIV/AIDS (Nie et al., 2020; Isaacson, 2021). The promise of CRISPR also offers the potential to eliminate forms of deafness and blindness or mental illnesses such as schizophrenia or depression. Those seem to be worthwhile goals, too, at least at first blush. But where do we draw the line? Should we be able to select the sex of our child, or decide our children’s sexual preferences? Is it OK to engineer our offspring to be taller, smarter, or physically stronger than average? In short, as we contemplate the wonders of what CRISPR can do, a question quickly emerges about whether it’s OK for us to impose our values—some would say our biases—on future generations. If you’re short, or female, or have autism, or are bisexual, such characteristics are probably an important part of your identity. It’s part of what makes you who you are. The notion of someone else deciding for you that you shouldn’t be that way purely because they themselves don’t like it is disturbing (Greene & Master, 2018; Isaacson, 2021). Clearly, it’s difficult to say where the line should be drawn, and whether your parents should determine what kind of person you will be in advance of your birth. At the same time, though, CRISPR offers great potential for the advancement of humankind and the alleviation of much suffering. But the technology creates many thorny questions about its appropriate use. Shared Writing Prompt Might there be any ways in which society and culture could be harmed if conditions such as depression or schizophrenia were eliminated via CRISPR? How so? 62 PART 1 Beginnings Module 2.1 Review LO 2.1 Describe how genes and chromosomes provide our basic genetic endowment. LO 2.5 Describe the field of behavioral genetics. In humans, the male sex cell (the sperm) and the female sex cell (the ovum) provide the developing baby with 23 chromosomes each. The field of behavioral genetics, a combination of psychology and genetics, studies the effects of genetics on behavior and psychological characteristics. LO 2.2 LO 2.6 Compare monozygotic twins with dizygotic twins. Monozygotic twins are twins who are genetically identical. Dizygotic twins result from two separate ova that are fertilized by two separate sperm at roughly the same time. LO 2.3 Describe how the sex of a child is determined. When an ovum and sperm meet at the moment of fertilization, the ovum provides an X chromosome, and the sperm provides either an X or a Y chromosome. If the sperm contributes an X chromosome, the child will have an XX pairing—a female. If the sperm contributes a Y chromosome, the result will be an XY pairing—a male. LO 2.4 Explain the mechanisms by which genes transmit information. A genotype is the underlying combination of genetic material present in an organism but invisible; a phenotype is the visible trait, the expression of the genotype. Describe the major inherited disorders produced by damaged or mutated genes. Several inherited and genetic disorders are caused by damaged or mutated genes. LO 2.7 Describe the role of genetic counselors and differentiate between different forms of prenatal testing. Genetic counselors use a variety of data and techniques to advise future parents of possible genetic risks to their unborn children. A variety of techniques can be used to assess the health of an unborn child if a woman is already pregnant, including ultrasound, CVS, and amniocentesis. Journal Prompt Applying Lifespan Development: How can the field of behavioral genetics help researchers understand human development? The Interaction of Heredity and Environment Like many other parents, Jared’s mother, Leesha, and his father, Jamal, tried to figure out which one of them their new baby resembled the most. He seemed to have Leesha’s big, wide eyes and Jamal’s generous smile. As he grew, Jared grew to resemble his mother and father even more. His hair grew in with a hairline just like Leesha’s, and his teeth, when they came, made his smile resemble Jamal’s even more. He also seemed to act like his parents. For example, he was a charming little baby, always ready to smile at people who visited the house—just like his friendly, jovial dad. He seemed to sleep like his mom, which was lucky because Jamal was an extremely light sleeper who could do with as little as 4 hours a night, while Leesha liked a regular 7 or 8 hours. Were Jared’s ready smile and regular sleeping habits something he just luckily inherited from his parents? Or did Jamal and Leesha provide a happy and stable home that encouraged these welcome traits? What causes our behavior? Nature or nurture? Is behavior produced by inherited, genetic influences, or is it triggered by factors in the environment? The simple answer is: There is no simple answer. for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development 63 The Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes LO 2.8 Explain how the environment and genetics work together to determine human characteristics. As developmental research accumulates, it is becoming increasingly clear that to view behavior as due to either genetic or environmental factors is inappropriate. A given behavior is not caused just by genetic factors, nor is it caused solely by environmental forces. Instead, as we first discussed in Chapter 1, the behavior is the product of some combination of the two. For instance, consider temperament, patterns of arousal and emotionality that represent consistent and enduring characteristics in an individual. Suppose we found—as increasing evidence suggests is the case—that a small percentage of children are born with temperaments that produce an unusual degree of physiological reactivity. Having a tendency to shrink from anything unusual, such infants react to novel stimuli with a rapid increase in heartbeat and unusual excitability of the limbic system of the brain. Such heightened reactivity to stimuli at the start of life, which seems to be linked to inherited factors, is also likely to cause children, by the time they are 4 or 5, to be considered shy by their parents and teachers. But not always: Some of them behave indistinguishably from their peers at the same age (De Pauw & Mervielde, 2011; Pickles et al., 2013; Smiley et al., 2016). What makes the difference? The answer seems to be the environment in which the children are raised. Children whose parents encourage them to be outgoing by arranging new opportunities for them may overcome their shyness. In contrast, children raised in a stressful environment marked by marital discord or a prolonged illness may be more likely to retain their shyness later in life (Kagan, 2010; Casalin et al., 2012; Merwin, Smith, Kushner, et al., 2017; Poole et al., 2020). Jared, described previously, may have been born with an easy temperament, which was easily reinforced by his caring parents. Such findings illustrate that many traits reflect multifactorial transmission, meaning that they are determined by a combination of both genetic and environmental factors. In multifactorial transmission, a genotype provides a particular range within which a phenotype may achieve expression. For instance, people with a genotype that permits them to gain weight easily may never be slim, no matter how much they diet. They may be relatively slim, given their genetic heritage, but they may never be able to get beyond a certain degree of thinness. In many cases, then, it is the environment that determines the way in which a particular genotype will be expressed as a phenotype (Plomin, 2016). By contrast, certain genotypes are relatively unaffected by environmental factors. In such cases, development follows a preordained pattern, relatively independent of the specific environment in which a person is raised. For instance, research on pregnant women who were severely malnourished during famines caused by World War II found that their children were, on average, unaffected physically or intellectually as adults (Stein et al., 1975). Similarly, no matter how much health food people eat, they are not going to grow beyond certain genetically imposed limitations in height. Little Jared’s hairline was probably affected little by any actions on the part of his parents. Ultimately, of course, the unique interaction of inherited and environmental factors determines people’s patterns of development. The more appropriate question, then, is how much of the behavior is caused by genetic factors, and how much by environmental factors? (See, for example, the range of possibilities for the determinants of intelligence, illustrated in Figure 2-8.) At one extreme is the idea that opportunities in the environment are solely responsible for intelligence; on the other, that intelligence is purely genetic—you either have it or you don’t. The usefulness of such extremes seems to be that they point us toward the middle ground—that intelligence is the result of some combination of natural mental ability and environmental opportunity (Asbury & Plomin, 2014). temperament patterns of arousal and emotionality that represent consistent and enduring characteristics in an individual INTERACTION OF FACTORS. multifactorial transmission the determination of traits by a combination of both genetic and environmental factors in which a genotype provides a range within which a phenotype may be expressed 64 PART 1 Beginnings Figure 2-8 Factors Impacting Intelligence Intelligence may be explained by a range of differing possible sources, spanning the nature–nurture continuum. Which of these explanations do you find most convincing, given the evidence discussed in the chapter? Possible Causes Nature Intelligence is provided entirely by genetic factors; environment plays no role. Even a highly enriched environment and excellent education make no difference. Nurture Although largely inherited, intelligence is affected by an extremely enriched or deprived environment. Intelligence is affected both by a person’s genetic endowment and environment. A person genetically predisposed to low intelligence may perform better if raised in an enriched environment or worse in a deprived environment. Similarly, a person genetically predisposed to higher intelligence may perform worse in a deprived environment or better in an enriched environment. Although intelligence is largely a result of environment, genetic abnormalities may produce mental retardation. Intelligence depends entirely on the environment. Genetics plays no role in determining intellectual success. Studying Development: How Much Is Nature? How Much Is Nurture? LO 2.9 Summarize how researchers study the interaction of genetic and environmental factors in development. Developmental researchers use several strategies to try to resolve the question of the degree to which traits, characteristics, and behavior are produced by genetic or environmental factors. Their studies involve both nonhuman species and humans. NONHUMAN ANIMAL STUDIES: CONTROLLING BOTH GENETICS AND ENVIRONMENT. It is relatively simple to develop breeds of animals that are geneti- cally similar to one another in terms of specific traits. The people who raise Butterball turkeys for Thanksgiving do it all the time, producing turkeys that grow especially rapidly so that they can be brought to market inexpensively. Likewise, strains of laboratory animals can be bred to share similar genetic backgrounds. By observing animals with similar genetic backgrounds in different environments, scientists can determine, with reasonable precision, the effects of specific kinds of environmental stimulation. For example, animals can be raised in unusually stimulating environments, with lots of items to climb over or through, or they can be raised in relatively barren environments, to determine the results of living in such different settings. Conversely, researchers can examine groups of animals that have been bred to have significantly different genetic backgrounds on particular traits. Then, by exposing such animals to identical environments, they can determine the role of genetic background. Of course, the drawback to using nonhumans as research subjects is that we can’t be sure how well the findings we obtain can be generalized to people. Still, animal research offers substantial opportunities. CONTRASTING RELATEDNESS AND BEHAVIOR: ADOPTION, TWIN, AND FAMILY STUDIES. Clearly, researchers can’t control either the genetic backgrounds or the environ- ments of humans in the way they can with nonhumans. However, nature conveniently has provided the potential to carry out various kinds of “natural experiments”—in the form of twins. Recall that monozygotic twins are identical genetically. Because their inherited backgrounds are precisely the same, any variations in their behavior must be due entirely to environmental factors. email Chapter 2 [email protected] The Start of Life: Prenatal Development Theoretically, identical twins would make great subjects for experiments about the roles of nature and nurture. For instance, by separating identical twins at birth and placing them in totally different environments, researchers could assess the impact of environment unambiguously. Of course, ethical considerations make this impossible. What researchers can—and do—study, however, are cases in which identical twins have been put up for adoption at birth and are raised in substantially different environments. Such instances allow us to draw fairly confident conclusions about the relative contributions of genetics and environment (Suzuki, & Ando, 2014; Strachan et al., 2017). The data from such studies of identical twins raised in different environments are not always without bias. Adoption agencies typically take the characteristics (and wishes) of birth mothers into account when they place babies in adoptive homes. For instance, children tend to be placed with families of the same race and religion. Consequently, even when monozygotic twins are placed in different adoptive homes, there are often similarities between the two home environments. As a result, researchers cannot always be certain that differences in behavior are due to differences in the environment. Studies of dizygotic twins also present opportunities to learn about the relative contributions of nature and nurture. Recall that dizygotic twins are genetically no more similar than siblings in a family born at different times. By comparing behavior within pairs of dizygotic twins with that of pairs of monozygotic twins (who are genetically identical), researchers can determine whether monozygotic twins are more similar in a particular trait, on average, than dizygotic twins. If so, they can assume that genetics plays an important role in determining the expression of that trait. Still another approach is to study people who are totally unrelated to one another and who therefore have dissimilar genetic backgrounds but who share an environmental background. For instance, a family that adopts, at the same time, two very young unrelated children probably will provide them with quite similar environments throughout their childhood. In this case, similarities in the children’s characteristics and behavior can be attributed with some confidence to environmental influences (Segal, 2000). Finally, developmental researchers have examined groups of people in light of their degree of genetic similarity. For instance, on the one hand, if we find a high association on a particular trait between biological parents and their children but a weaker association between adoptive parents and their children, we have evidence for the importance of genetics in determining the expression of that trait. On the other hand, if there is a stronger association on a trait between adoptive parents and their children than between biological parents and their children, we have evidence for the importance of the environment in determining that trait. If a particular trait tends to occur at similar levels among genetically similar individuals but occurs at different levels among genetically more distant individuals, signs point to the fact that genetics plays an important role in the development of that trait. Developmental researchers have used all these approaches, and more, to study the relative impact of genetic and environmental factors. What have they found? Before turning to specific findings, here’s the general conclusion resulting from decades of research. Virtually all traits, characteristics, and behaviors are the joint result of the combination and interaction of nature and nurture. Genetic and environmental factors work in tandem, each affecting and being affected by the other, creating the unique indi- Monozygotic and dizygotic twins present opportunities to learn about the relative vidual that each of us is and will become (Robinson, contributions of heredity and situational factors. What can psychologists learn from 2004; Waterland & Jirtle, 2004; Kendler et al., 2017). studying twins? 65 Alex Slitz/ZUMA Wire/ZUMAPRESS.com/Alamy Stock Photo for more ebook/ testbank/ solution manuals requests: 66 PART 1 Beginnings TRANSGENERATIONAL EPIGENETIC INHERITANCE: WHEN NATURE BECOMES NURTURE. A fundamental assumption about genetic inheritance has long been that environmental alterations of an organism’s health cannot be passed down to future generations; if we cut off a mouse’s tail, we do not expect its offspring to be tailless. Only genetic mutations—not lifestyle choices such as poor diet nor environmental insults such as exposure to toxins—were thought to be heritable. But recent research finds that an individual’s life experiences can be passed down to children, grandchildren, and subsequent generations. It’s a phenomenon called transgenerational epigenetic inheritance, and it works a bit differently from usual inheritance. Instead of changing the genetic code itself, life experiences change the parts of DNA that switch individual genes on or off. Not every gene is active everywhere in the body; the DNA that is responsible for making insulin, for example, is only “switched on” in certain cells of the pancreas. When an event such as malnourishment or drug use affects the DNA “switches” in sperm or eggs, the alterations can be passed on to future generations (Daxinger & Whitelaw, 2012; Bahenko et al., 2016; Nestler, 2016; Satterlee et al., 2019; Aygun & Bjornsson, 2020; Guerrero et al., 2020). In one study, healthy male rats were fed a high-fat diet that caused them to put on weight and develop symptoms consistent with type 2 diabetes, such as insulin resistance. Although these rats did not have a preexisting genetic tendency to be diabetic, their daughters also developed symptoms of type 2 diabetes as adults—even though they ate normal diets. Some researchers think that transgenerational epigenetic inheritance could partly explain the epidemic of childhood obesity: Our high-fat diets may not only put us at risk but, perhaps, our children as well (Skinner, 2010; Crews et al., 2012; Kowluru, 2017; Candler et al., 2019). Happily, it’s not just harmful effects that can be passed on this way. One study showed that mice developed better memory after being exposed to an enriched and stimulating environment, as previous research showed would be the case, and that the mice’s offspring also showed the beneficial memory effect even though they didn’t experience the same enriched environment. The implications of this research are astounding; it may well be the case that the poor life choices we make in our youth have consequences for our progeny as well as ourselves (Heard & Martienssen, 2014; Eagle et al., 2019; Aygun & Bjornsson, 2020). Genetics and the Environment: Working Together LO 2.10 Explain how genetics and the environment jointly influence physical traits, intelligence, and personality. Let’s look at ways in which genetics and the environment influence our physical traits, intelligence, and personality. PHYSICAL TRAITS: FAMILY RESEMBLANCES. When patients entered the examining room of Dr. Cyril Marcus, they didn’t realize that sometimes they were actually being treated by his identical twin brother, Dr. Stewart Marcus. So similar in appearance and manner were the twins that even longtime patients were fooled by this admittedly unethical behavior, which occurred in a bizarre case made famous in the film Dead Ringers. Monozygotic twins are merely the most extreme example of the fact that the more genetically similar two people are, the more likely they are to share physical characteristics. Tall parents tend to have tall children, and short ones tend to have short children. Obesity, which is defined as being more than 20 percent above the average weight for a given height, also has a strong genetic component. For example, in one study, pairs of identical twins were put on diets that contained an extra 1,000 calories a day—and ordered not to exercise. Over a 3-month period, the twins gained almost identical amounts of weight. Moreover, different pairs of twins varied substantially in how much weight they gained, with some pairs gaining almost 3 times as much weight as other pairs (Bouchard et al., 1990). for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development Other, less obvious physical characteristics also show strong genetic influences. For instance, blood pressure, respiration rates, and even the age at which life ends are more similar in closely related individuals than in those who are less genetically alike (Melzer et al., 2007; Wu et al., 2013). No other issue involving the relative influence of heredity and environment has generated more research than the topic of intelligence. Why? The main reason is that intelligence, generally measured in terms of an IQ score, is a central characteristic that differentiates humans from other species. In addition, intelligence is strongly related to success in scholastic endeavors and, somewhat less strongly, to other types of achievement. Genetics plays a significant role in intelligence. In studies of both overall or general intelligence and of specific subcomponents of intelligence (such as spatial skills, verbal skills, and memory), as can be seen in Figure 2-9, the closer the genetic link between two individuals, the greater the correspondence of their overall IQ scores. The impact of genetics on intelligence also increases with age. For instance, as fraternal (dizygotic) twins move from infancy to adolescence, their IQ scores become less similar. In contrast, the IQ scores of identical (monozygotic) twins become increasingly similar over the course of time. These opposite patterns suggest the intensifying influence of inherited factors with increasing age (Segal et al., 2014; Madison et al., 2016; de Zwarte et al., 2019). Although it is clear that heredity plays an important role in intelligence, investigators are much more divided on the question of the degree to which it is inherited. Perhaps the most extreme view is held by psychologist Arthur Jensen (2011), who argued that as much as 80 percent of intelligence is a result of heredity. Others have suggested more modest figures, ranging from 50 to 70 percent. It is critical to recall that such figures are averages across large groups of people, and any particular individual degree of inheritance cannot be predicted from these averages (Brouwer et al., 2014; Schmiedek, 2017). INTELLIGENCE: MORE RESEARCH, MORE CONTROVERSY. Figure 2-9 Genetics and IQ The closer the genetic link between two individuals, the greater the correspondence between their IQ scores. Why is there a difference in the median correlation of IQs between children reared together and siblings reared together? Alternatively, why is there a difference in the median correlation of IQs between children reared together and siblings reared apart? How would you characterize the influence of genetics and environment on IQ? (Source: Based on Bouchard & McGue, 1981.) Median Correlation 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Genetic Overlap 0% 50% 50% 50% 50% 50% 100% 100% re n to re ge ar th ed Fo er st er pa re n ch t & Si ild bl in gs re a ap re ar d Pa t re nt & ch Si ild bl in gs to re ge ar th ed Fr er at e di rn ff al er tw en i t s ns Fr ex , at er na sa l tw m i e ns Id se , en x t re ica ar l ed tw ap ins ar , I t re den ar ti ed ca to l tw ge in th s, er Ch ild Relationship 0% 67 68 PART 1 Beginnings It is also important to keep in mind that, whatever role heredity plays, environmental factors such as exposure to books, good educational experiences, and intelligent peers are profoundly influential. Consequently, in terms of public policy, we need to focus on the environmental influences that are geared toward maximizing the intellectual development of each individual. From an Educator’s Perspective Some people have used the proven genetic basis of intelligence to argue against strenuous educational efforts on behalf of individuals with below-average IQs. Does this viewpoint make sense based on what you have learned about heredity and environment? Why or why not? dotshock/Shutterstock GENETIC AND ENVIRONMENTAL INFLUENCES ON PERSONALITY: BORN TO BE OUTGOING? Do we inherit our personality? At least in part. There’s increasing research evidence suggesting that some of our most basic personality traits have genetic roots. For example, two of the key “Big Five” personality traits, neuroticism and extroversion, have been linked to genetic factors. Neuroticism, as used by personality researchers, is the degree of emotional stability an individual characteristically displays. Extroversion is the degree to which a person seeks to be with others, to behave in an outgoing manner, and generally to be sociable. For instance, Jared, the baby described previously in this chapter, may have inherited a tendency to be outgoing from his extroverted father, Jamal (Horwitz et al., 2008; Zyphur et al., 2013; Briley & Tucker-Drob, 2017). How do we know which personality traits reflect genetics? Some evidence comes from direct examination of genes themselves. For instance, a specific gene is influential in determining risk-taking behavior. This novelty-seeking gene affects the production of the brain chemical dopamine, making some people more prone than others to seek out novel situations and to take risks (Ray et al., 2009; Veselka et al., 2012; Lachmann et al., 2020). Other evidence for the role of genetics in determining personality traits comes from studies of twins. For instance, in one major study, researchers looked at the personality traits of hundreds of pairs of twins. Because a good number of the twins were genetically identical but had been raised apart, it was possible to determine with some confidence the influence of genetic factors (Tellegen et al., 1988). The researchers found that certain traits reflected the contribution of genetics considerably more than others. As you can see in Figure 2-10, social potency (the tendency to be a masterful, forceful leader who enjoys being the center of attention) and traditionalism (strict endorsement of rules and authority) are strongly associated with genetic factors (Harris et al., 2007; South et al., 2015). Even more complicated personality traits are linked to genetics. For example, political attitudes, religious interests and values, and even attitudes toward human sexuality have genetic components (Kandler et al., 2012; Schermer & Martin, 2019; Gordovez & McMahon, 2020). Clearly, genetic factors play a role in determining personality. At the same time, the environment in which a child is raised also affects personality development. For example, some parents encourage high activity levels, seeing activity as a manifestation of independence and intelligence. Other parents may encourage lower levels of activity in their children, feeling that more passive children will get along better in society. These parental attitudes are in part culturally determined; parents in the United Although genetic factors clearly play a significant role in the development of intelStates may encourage higher activity levels, ligence, the level of environmental enrichment is also crucial. for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development Figure 2-10 Inheriting Traits These traits are among the personality factors that are related most closely to genetic factors. The higher the percentage, the greater the degree to which the trait reflects the influence of heredity. Do these figures mean that “leaders are born, not made”? Why or why not? (Source: Adapted from Tellegen et al., 1988.) Social potency 61% Is masterful, a forceful leader who likes to be the center of attention. Traditionalism 60% Follows rules and authority, endorses high moral standards and strict discipline. Stress reaction 55% Feels vulnerable and sensitive and is given to worries and is easily upset. Absorption 55% Has a vivid imagination readily captured by rich experience; relinquishes sense of reality. Alienation 55% Feels mistreated and used, that “the world is out to get me.” Well-being 54% Has a cheerful disposition, feels confident and optimistic. Harm avoidance 50% Shuns the excitement of risk and danger, prefers the safe route even if it is tedious. Aggression 48% Is physically aggressive and vindictive, has taste for violence and is “out to get the world.” Achievement 46% Works hard, strives for mastery, and puts work and accomplishment ahead of other things. Control 43% Is cautious and plodding, rational and sensible, likes carefully planned events. Social closeness 33% Prefers emotional intimacy and close ties, turns to others for comfort and help. whereas parents in Asian cultures may encourage greater passivity. In both cases, children’s personalities will be shaped in part by their parents’ attitudes (Cauce, 2008; Luo et al., 2017; Mącik, 2021). Because both genetic and environmental factors have consequences for a child’s personality, personality development is a perfect example of a central fact of child development: Nature and nurture are closely intertwined. Furthermore, the way in which nature and nurture interact can be reflected not just in the behavior of individuals but also in the foundations of a culture, as we see next. Psychological Disorders: The Role of Genetics and Environment LO 2.11 Explain the role genetics and the environment play in the development of psychological disorders. When Elani Dimitrios turned 13, her cat, Mefisto, began to give her orders. At first the orders were harmless: “Wear two different socks to school” or “Eat out of a bowl on the floor.” Her parents dismissed these events as signs of a vivid imagination, but when Elani approached her little brother with a hammer, her mother intervened forcibly. Elani later recalled, “I heard the order very clearly: Kill him, kill him. It was as if I was possessed.” In a sense, she was possessed: possessed with schizophrenia spectrum disorder, one of the most severe types of psychological disorders (typically referred to more simply as schizophrenia). Normal and happy through childhood, Elani increasingly lost her hold on reality as she entered adolescence. For the next three decades, she would be in and out of institutions, struggling to ward off the ravages of the disorder. 69 70 PART 1 Beginnings What was the cause of Elani’s mental disorder? Increasing evidence suggests that schizoThe psychological disorder schizophrenia has clear genetic components. The phrenia is brought about by genetic factors. The closer the genetic links between someone with schizophrenia and another family disorder runs in families, with some families member, the more likely it is that the other person will also develop schizophrenia. showing an unusually high incidence. Moreover, (Source: Based on Gottesman, 1991.) the closer the genetic links between someone Lifetime Risk of Developing Schizophrenia 50 with schizophrenia and another family member, the more likely it is that the other person will also develop schizophrenia. For instance, a 40 monozygotic twin has close to a 50 percent risk of developing schizophrenia when the other 30 twin develops the disorder (see Figure 2-11). By contrast, a niece or nephew of a person with 20 schizophrenia has less than a 5 percent chance of developing the disorder (Mitchell & Porteous, 2011; van Haren et al., 2012; Corvin et al., 2020). 10 These data also illustrate that genetics alone does not influence the development of 0 the disorder. If genetics were the sole cause, the 1% 2% 2% 2% 4% 5% 6% 13% 9% 17% 17% 6% 48% risk for an identical twin would be 100 percent. Consequently, other factors account for the disorder, ranging from structural abnormalities in the brain to a biochemical imbalance (e.g., Lyons et al., 2002; Hietala et al., 2003; Howes & Kapur, 2009; Wada et al., 2012). It also seems that even if individuals harbor a genetic predisposition toward schizophrenia, they are not destined to develop the disorder. Instead, they may inherit an unusual sensitivity to stress in the environment. If stress is low, schizophrenia will not occur. But if stress is sufficiently strong, it will lead to schizophrenia. At the same time, for someone with a strong genetic predisposition toward the disorder, even relatively weak environmental stressors may lead to schizophrenia (Mittal et al., 2008; Walder et al., 2014). Several other psychological disorders have been shown to be related, at least in part, to genetic factors. For instance, major depressive disorders, alcoholism, autism spectrum disorder, and attention-deficit/hyperactivity disorder have significant inherited components (Burbach & van der Zwaag, 2009; Cho et al., 2017; Lai et al., 2020). The example of schizophrenia spectrum disorder and other genetically related psychological disorders also illustrates a fundamental principle regarding the relationship between heredity and environment, a principle that underlies much of our previous discussion. Specifically, the role of genetics is often to produce a tendency toward a future course of development. When and whether a certain behavioral characteristic will actually be displayed depends on the nature of the environment. Thus, although a predisposition for schizophrenia may be present at birth, typically people do not show the disorder until adolescence—if at all. Similarly, certain other kinds of traits are more likely to be displayed as the influence of parents and other socializing factors declines. For example, adopted children may, early in their lives, display traits that are relatively similar to their adoptive parents’ traits, given the overwhelming influence of the environment on young children. As they get older and their parents’ day-to-day influence declines, genetically influenced traits may begin to manifest themselves as unseen genetic factors begin to play a greater role. In fact, some researchers argue that parents’ treatment of their children plays a decreasing role in determining their children’s personality traits and behavior as children age. The minimalization of parental influence occurs for two reasons. First, genetics consistently plays a significant role, so much so that it may be as much or even more influential that the environment that parents create for their children. Second, as children get older, they are increasingly influenced by their friends, peers, and other adults such as teachers. Consequently, parenting effects seem to decline in importance as children age (Ayoub et al., 2019; Wolfson, 2020). ild bl i re w ng n ith s w S ib sc ith lin hi 1 zo p gs D ph ar iz e yg ren nt ot ia ic tw M in on s P oz ar en yg ts ot ic tw in s gs Ch Si n in bl si f- H al ch ild re ce G ra nd N s/ he ep N s ts ie un A s/ le w s nc U Fi rs tc ou si nt n tie tio la s of pa pu po se al ou er Sp en G ns Degree of Risk Figure 2-11 The Genetics of Schizophrenia for more ebook/ testbank/ solution manuals requests: email Chapter 2 [email protected] The Start of Life: Prenatal Development 71 Developmental Diversity and Your Life Cultural Differences in Physical Arousal: Might a Culture’s Philosophical Outlook Be Determined by Genetics? Buddhist philosophy, an inherent part of many Asian cultures, any single individual within a culture can be more or less emphasizes harmony and peacefulness. In contrast, some temperamentally volatile and that the range of temperaments traditional Western philosophies, such as those of Martin Luther found even within a particular culture is vast. Finally, as and John Calvin, accentuate the importance of controlling the noted in our initial discussion of temperament, environmental anxiety, fear, and guilt that they assume to be basic parts of the conditions can have a significant effect on the portion of a human condition. person’s temperament that is not genetically determined. But what Kagan and his colleagues’ speculation does attempt to Could such philosophical approaches reflect, in part, genetic factors? That is the controversial suggestion made by address is the back-and-forth-interchange between culture developmental psychologist Jerome Kagan and his colleagues. and temperament. As religion may help mold temperament, They speculate that the underlying temperament of a given so may temperament make certain religious ideals more society, determined genetically, may predispose people in that attractive. The notion that the basis of culture—its philosophical society toward a particular philosophy (Kagan, 2003, 2010). traditions—may be affected by genetic factors is intriguing. Kagan bases his admittedly speculative suggestion on wellconfirmed findings that show clear differences in temperament More research is necessary to determine just how the unique between white and Asian children. For instance, one study that interaction of heredity and environment within a given culture compared 4-month-old infants in China, Ireland, and the United may produce a framework for viewing and understanding States found several relevant differences. In comparison to the the world. white American babies and the Irish babies, the Chinese babies had significantly lower motor activity, irritability, and vocalization (see Table 2-4). Kagan suggests that the Chinese, who enter the world temperamentally calmer, may find Buddhist philosophical In contrast, Westerners, who are emotionally more volatile and tense, and who report higher levels of guilt, are more likely to be attracted to philosophies that articulate the necessity of controlling the unpleasant feelings that they are more apt to encounter in their everyday experience (Kagan, 2003, 2010). It is important to note that this does not mean that one philosophical approach is necessarily better or worse than the other. Nor does it mean that either of the temperaments from which the philosophies are thought to spring is superior or inferior to the other. Similarly, we must remember that Ingram Publishing/Newscom notions of serenity more in tune with their natural inclinations. Buddhist philosophy emphasizes harmony and peacefulness. Could this decidedly non-Western philosophy be caused, in part, by genetics? Table 2-4 Mean Behavioral Scores for White American, Irish, and Chinese 4-Month-Old Infants Behavior White American Irish Chinese 48.6 36.7 11.2 7.0 2.9 1.1 Fretting (% trials) 10.0 6.0 1.9 Vocalizing (% trials) 31.4 31.1 8.1 4.1 2.6 3.6 Motor activity Crying (in seconds) Smiling (% trials) (Source: Kagan et al., 1993.) 72 PART 1 Beginnings Can Genes Influence the Environment? LO 2.12 Describe ways in which genes influence the environment. According to developmental psychologist Sandra Scarr (1993, 1998), the genetic endowment provided to children by their parents not only determines their genetic characteristics but also actively influences their environment. Scarr suggests three ways a child’s genetic predisposition might influence their environment. Children tend to actively focus on those aspects of their environment that are most connected with their genetically determined abilities. For example, an active, more aggressive child will gravitate toward sports, whereas a more reserved child will be more engaged by academics or solitary pursuits such as computer games or drawing. Children also pay less attention to those aspects of the environment that are less compatible with their genetic endowment. For instance, two girls may be reading the same school bulletin board. One may notice the sign advertising tryouts for Little League baseball, and her less coordinated but more musically endowed friend might be more apt to spot the notice recruiting students for an after-school chorus. In each case, the child is attending to those aspects of the environment in which her genetically determined abilities can flourish. In some cases, the gene–environment influence is more passive and less direct. For example, a particularly sports-oriented parent, who has genes that promote good physical coordination, may provide many opportunities for a child to play sports. Finally, the genetically driven temperament of a child may evoke certain environmental influences. For instance, an infant’s demanding behavior may cause parents to be more attentive to the infant’s needs than they would be if the infant were less demanding. Or, for instance, a child who is genetically inclined to be well coordinated may play ball with anything in the house so often that the parents notice. They may then decide that the child should have some sports equipment. In sum, determining whether behavior is primarily attributable to nature or nurture is a bit like shooting at a moving target. Not only are behaviors and traits a joint outcome of genetic and environmental factors but the relative influence of genes and environment for specific characteristics also shifts over the course of people’s lives. Although the pool of genes we inherit at birth sets the stage for our future development, the constantly shifting people in our lives—parents, friends, teachers, and so forth—determine just how our development eventually plays out. The environment both influences our experiences and is molded by the choices we are temperamentally inclined to make. Module 2.2 Review LO 2.8 Explain how the environment and genetics work together to determine human characteristics. Human characteristics and behavior often reflect multifactorial transmission, meaning that they are a joint outcome of genetic and environmental factors. LO 2.9 Summarize how researchers study the interaction of genetic and environmental factors in development. Developmental researchers use a number of strategies to examine the extent to which traits and behavior are due to genetic factors or environmental factors. Strategies include animal studies and research on twins, adopted siblings, and families. LO 2.10 Explain how genetics and the environment jointly influence physical traits, intelligence, and personality. Genetic influences have been identified in physical characteristics, intelligence, and personality traits and behaviors. Environmental factors, such as family dispositions and habits, also play a role in such traits as intelligence and personality. LO 2.11 Explain the role genetics and the environment play in the development of psychological disorders. Schizophrenia spectrum disorder has strong genetic roots. Other disorders, including major depressive disorder, alcoholism, autism spectrum disorder, and attention-deficit/hyperactivity for more ebook/ testbank/ solution manuals requests: disorder, have genetic components as well, but environmental influences also contribute. LO 2.12 Describe ways in which genes influence the environment. Children may influence their environment through genetic traits that cause them to construct—or influence their parents to construct—an environment that mat