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Evolution, Genetics, and Experience ➔ Mutations, recombinations, and microduplications of genes introduce new Thinking about the Biology of Behavior heritable variations that help or ha...

Evolution, Genetics, and Experience ➔ Mutations, recombinations, and microduplications of genes introduce new Thinking about the Biology of Behavior heritable variations that help or harm an individual’s chance of surviving and reproducing. Biology of Behavior ➔ Certain individuals successfully reproduce more than others do, thus - All behavior is the product of interactions among three factors: passing on their genes to the next generation. Any gene that is associated 1. the organism’s genetic endowment, which is a product of its with greater reproductive success will become more prevalent in later evolution generations. 2. its experience 3. its perception of the current situation Evolution of the Human Brain ❖ Three important points about the evolution of the human brain: Evolution of Behavior - It has increased in size during evolution. - Evolution is a change over generations in the frequencies of various - Most of the increase in size has occurred in the cerebrum. genes in a population. - An increase in the number of convolutions folds on the cerebral - Evolution includes any change in gene frequencies, regardless of surface has greatly increased the volume of the cerebral cortex. whether it helps or harms the species in the long run. ❖ Although there are differences among the brains of related species, there is a fundamental similarity: Evolution - All brains are constructed of neurons ❖ Charles Darwin argued that evolution occurs through natural selection. - The neural structures in the brains of one species can usually be ❖ Heritable traits that are associated with high rates of survival and found in the brains of related species reproduction are the most likely ones to be passed onto future ❖ Human beings have experienced very rapid brain growth, possibly in generations. response to the challenges of using tools, language, social behavior, and ❖ When repeated for generation after generation, it leads to the evolution of learning to plan for the future. species that are better adapted to surviving and reproducing in their particular environmental niche. Have humans stopped evolving? ❖ Evolution does not always proceed slowly and gradually. - Rapid evolutionary changes can be triggered by sudden changes in the environment or by adaptive genetic mutations. ❖ Not all existing behaviors or structures are adaptive. - The incidental non-adaptive evolutionary by-products are called spandrels. ❖ Behaviors or structures that were once adaptive might become nonadaptive, or even maladaptive, if the environment changes. ❖ Not all existing adaptive characteristics evolved to perform their current function. Does “evolution” mean “improvement”? ❖ Similarities among species do not necessarily mean that the ❖ species have common evolutionary origins. ❖ Homologous- Structures that are similar because they have a common evolutionary origin. ❖ Analogous - structures that are similar but do not have a common evolutionary origin. How do species evolve? ➔ Offsprings generally resemble their parents for genetic reasons.  ❖ Females have twice the chance of inheriting the dominant gene because ❖ Evolution spreads the genes of the individuals who have reproduced the they have twice the number of X chromosomes. In contrast, recessive most. sex-linked traits occur more frequently in males. Genetics and Behavior Mendelian Genetics ❖ Mechanisms of Heredity. The science of genetics is the study of heredity (the genetic transmission of heritable characteristics from parents to offspring). ❖ The basic functional units of heredity are the genes. ❖ Genes-units of heredity that maintain their structural identity from one generation to another 1. Mendel proposed that there are two kinds of inherited factors for each ❖ DNA carries the biochemical dichotomous trait. instructions, or genetic code, that Dichotomous traits - traits that occur in one form or the other, governs the development of cell never in combination. functions. Ex. seed color is a dichotomous pea plant trait: Every pea plant ❖ Each gene is located by function has either brown seeds or white seeds. in a definite position on a Each inherited factor = gene. particular chromosome. ❖ The complete sequence of genes in the human body is called the human 2. Mendel proposed that each organism possesses two genes for each of its genome. dichotomous traits. Ex. each pea plant possesses either two brown-seed genes, two Chromosomes white-seed genes, or one of each. ❖ At conception, each normal human being Organisms that possess two identical genes for a trait are said receives 23 chromosomes from the mother to be homozygous for that trait; those that possess two and 23 from the father. different genes for a trait are said to be heterozygous for that ❖ These form 23 pairs of chromosomes—22 trait. pairs of autosomes and 1 pair of sex chromosomes. 3. Mendel proposed that one of the two kinds of genes for each dichotomous ❖ A child who receives an X chromosome from trait dominates the other in heterozygous organisms. each parent is genetically female. A child Ex. pea plants with a brown-seed gene and a white-seed gene who receives a Y chromosome from the always have brown seeds because the brown-seed gene always father is genetically male. dominates the white-seed gene. Sex Chromosomes and Sex-Linked Traits 4. Mendel proposed that for each dichotomous trait, each organism randomly ❖ Traits that are influenced by genes on the sex chromosomes are referred to inherits one of its fathers two factors and one of its mothers two factors. as sex-linked traits. ❖ Traits that are controlled by genes on the X chromosome occur more Genes frequently in one sex than the other. If the trait is dominant, it occurs ❖ Genes are chemicals that maintain their integrity from one generation to the more frequently in females. next and influence the development of the individual. ❖ A dominant gene affects development regardless of whether a person has pairs of that gene or only a single copy per cell.  ❖ A recessive gene affects development only in the absence of the dominant TURNER SYNDROME gene. ➔ results from a missing sex chromosome (XO). ➔ a condition that affects only Genotypes and Phenotypes: Multifactorial Transmission females. ➔ results when one of the X chromosomes (sex chromosomes) is missing or partially missing. ➔ can cause a variety of medical and developmental problems, including short height webbed neck, swollen hands and feet, failure of the ovaries to develop and heart defects. PHENOTYPE Observable characteristics of a person. GENOTYPE Genetic makeup of a person, containing both expressed and Nature and Nurture: Influences of Heredity and Environment unexpressed characteristics. ❖ Research in behavioral genetics is based on the assumption that the relative influences of heredity and environment within a population can be Chromosomal Abnormalities measured statistically. ❖ It typically occur because of errors in cell division, resulting in an extra or ❖ If heredity is an important influence on a trait, genetically closer persons will missing chromosome. be more similar in that trait. Example: ❖ Family studies, adoption studies, and studies of twins enable DOWN SYNDROME researchers to measure the heritability of specific traits. ➔ a chromosomal disorder characterized by moderate-to-severe mental retardation and by such physical signs as a downward sloping skin fold at the inner corners of the eyes. ➔ The condition is also called trisomy-21 because it is characterized in more than 90 percent of cases by an extra 21st chromosome. KLINEFELTER SYNDROME ➔ caused by an extra female sex chromosome (shown by the Gene-environment Correlations (rGE) pattern XXY). 1. Passive gene-environment correlation ➔ Symptoms may include breast 2. Evocative gene-environment correlation growth, infertility, osteoporosis 3. Active gene-environment correlation and learning difficulties.  1. Passive Gene-Environment Correlation raised separately. However, researchers have discovered that the ❖ The person’s environment, particularly in the case of children, is phenotype of identical twins grows apart as they age. largely determined by the parent’s genetic characteristics. ❖ Parents create a home environment that is influenced by Adoption Studies their own heritable characteristics. ➔ In adoption studies, identical twins raised by ❖ Ex. An intelligent parent is likely to create a home environment different families can give insight into the rich in educational materials and experience. nature-versus-nurture debate. ➔ Since the child is being raised by parents who 2. Evocative Gene-Environment Correlation are genetically different from his or her ❖ happens when an individual’s (heritable) behavior evokes an biological parents, the influence of the environmental response. environment shows how similar the child ❖ Ex. The association between marital conflict and depression may is to his or her adoptive parents or reflect the tension that arise when engaging with a depressed siblings. spouse rather than a causal effect of marital conflict that creates the risk for depression. Nature states the inheritance and the foundational structure of the human being while the environment in 3. Active Gene-Environment Correlation which a person is raised can trigger expressions of behavior for which that person is ❖ the person’s genetic makeup may lead him to select particular genetically predisposed. environments. ❖ Ex.: A shy person is likely to choose quiet activities and less Genetically identical people raised in different environments may exhibit boisterous environments than an extroverted individual. different behavior. Adoption and Twin Studies in the Nature vs. Nurture Debate Behavioral Development: Interaction of Genetic Factors and Experience ❖ Most behavioral variations reflect the combined influences of genes and environmental factors. ❖ Heritability is an estimate of the amount of variation that is due to genetic variation as opposed to environmental variation. ❖ Researchers estimate heritability of a human condition: - by comparing monozygotic and dizygotic twins - by comparing adopted children to their biological and adoptive parents. Adoption and Twin Studies in the Nature vs. Nurture Debate Twin Studies ➔ Studies of adult twins are used to investigate which traits are heritable. ➔ Identical twins share the same genotype. ➔ Twins raised apart tend to be similar in intelligence and, in some cases, life events and circumstances, when studied years later, even as they were