Psychology Chapter 2: Evolution, Genetics, and Experience

Origins of Dichotomous Thinking

• The concept of dichotomous thinking emerged in Western culture, where the Church's views were considered true.
• Around 1400, changes occurred with the plague, famines, and other events, leading to a shift in thinking.
• René Descartes (1596-1650) advocated for a philosophy that divided the universe into two parts:
  • Physical matter (behaves according to natural laws and is suitable for scientific investigation)
  • Human mind (soul, self, spirit; lacks physical substance, controls human behavior, and obeys no natural laws)

The Nature-Nurture Debate

• The nature-nurture debate revolves around whether humans and other animals inherit their behavioral capacities or acquire them through learning.
• John B. Watson (nurture) argued that there is no evidence of inheritance of behavioral traits.
• Ethology (nature) emphasizes the role of genetics in shaping behavior.

Problems with Traditional Dichotomies

• Brain damage can impact psychological functioning, as seen in the case of asomatognosia (the man who fell out of bed).
• Chimps exhibit human-like psychological abilities, such as self-awareness and psychological complexity.
• Factors other than genetics and learning, such as fetal environment, nutrition, and stress, influence behavioral development.

Model of Biology of Behavior

• All behavior is the product of interactions among three factors:
  1. The organism's genetic endowment
  2. Experience
  3. Perception of the current situation

Human Evolution

• Modern biology began with Charles Darwin's publication of "On the Origin of Species" in 1859.
• Darwin suggested evolution through natural selection, where members of each species vary in their structure, physiology, and behavior.
• Evolution of vertebrates:
  • Complex multicellular water-dwelling organisms emerged 800 million years ago.
  • Chordates (animals with dorsal nerve cords) evolved 250 million years later.
  • Vertebrates (animals with spinal bones) evolved 25 million years later.
• Evolution of amphibians:
  • Bony fishes started to venture out of water 410 million years ago.
  • Fins and gills transformed into legs and lungs, leading to the evolution of amphibians 370 million years ago.
• Evolution of reptiles:
  • Reptiles evolved from a branch of amphibians 315 million years ago.
  • They developed shell-covered eggs and dry scales, reducing their reliance on watery habitats.
• Evolution of mammals:
  • A new class of vertebrates evolved from small reptile lines 225 million years ago.
  • Females nurture their young in a watery environment within their bodies until birth.
• Emergence of humankind:
  • Humans, known as hominins, evolved from Australopithecus around 4 million years ago.
  • Homo sapiens emerged 275,000 years ago.

Thinking about Human Evolution

• Evolution does not proceed in a single line.
• Humans have no reason to claim evolutionary supremacy.
• Evolution does not always proceed slowly; rapid changes can be triggered by sudden environmental changes.
• Fewer than 1% of all known species are still in existence.

Evolution of the Human Brain

• There is no clear relationship between overall brain size and intelligence.
• Brains have increased in size during evolution.
• The number of convolutions (folds on the cerebral surface) has greatly increased the surface area of the cerebral cortex.

Understanding Mate Bonding

• Most mate bonds are promiscuous.
• Most mammals form polygynous mating bonds.
• Polyandry is rare in mammals.
• Humans generally form monogamous bonds.
• Mate bonding in humans is predicted through evolutionary theory.

Fundamental Genetics

• Mendelian genetics:
  • Dichotomous traits occur in one form or another, but never in combination.
  • True breeding lines are breeding lines where interbred members always produce offspring with the same trait.
• Chromosomes:
  • Genes are located on chromosomes.
  • Humans have 23 pairs of chromosomes with an allele on each chromosome.
  • Meiosis (produce gametes) involves the division of chromosomes, and one of each pair goes to each of the two gametes.
  • Mitosis follows meiosis, doubling the number of chromosomes.

Structure and Replication

• Each chromosome is a double-stranded molecule of DNA.
• DNA replication involves the unwinding of two strands, and complementary bases attract each other.
• Clinical consequences of chromosome replication:
  • Down syndrome (extra chromosome)
  • Mutation (alterations of individual genes)

Sex Chromosomes and Sex-Linked Traits

• Sex chromosomes are X and Y.
• Sex-linked traits are influenced by genes on the sex chromosomes.
• Dominant traits on the X chromosome are seen more in females.
• Recessive traits are seen more in males.
• Color blindness is rare in females.

Genetic Code and Gene Expression

• Promoters: stretches of DNA that determine whether or not particular structural genes are converted into proteins.
• Activators: proteins that bind to DNA and increase gene expression.
• Repressors: proteins that bind to DNA and decrease gene expression.
• Gene expression involves two phases:
  1. Transcription: the conversion of DNA into mRNA.
  2. Translation: the conversion of mRNA into protein.
• Epigenetics: the study of mechanisms of inheritance other than those mediated by changes to the DNA sequence.

Human Genome Project

• The purpose of the Human Genome Project is to compile a map of the sequence of all 3 billion nucleotide bases that compose human chromosomes.
• Protein-encoding genes constitute only about 1% of human DNA.
• The Human Proteome: a nearly complete map of the entire set of proteins encoded by human genes.

Modern Genetics and the Growth of Epigenetics

• Epigenetics: the study of all mechanisms of inheritance other than those mediated by changes to the DNA sequence.
• Four factors that led to the rise of epigenetics:
  • The Human Genome Project generated an arsenal of new research techniques.
  • Protein-coding genes constitute only about 1% of human DNA.
  • Protein encoding is only a minor function of RNA.
  • The mechanism of gene-environment interaction is unknown.
• Five important advances in epigenetics:
  • Non-gene DNA is no longer accepted.
  • Variety of different types of small RNA molecules.
  • Gene expression can be regulated by DNA methylation, histone remodeling, and RNA editing.
  • Epigenetic mechanisms can be enduring.
  • Transgenerational epigenetics examines the transmission of experiences via epigenetic mechanisms across generations.

Epigenetics on Behavioral Development: Interaction of Genetic Factors and Experience

• Selective breeding of maze-bright and maze-dull rats:
  • Tyron's experiment showed that selective breeding based on one behavioral trait brings a host of other behavioral traits along with it.
  • Maze-dull rats made more errors only when reared in impoverished environments.
• Phenylketonuria (PKU): a single metabolic disorder:
  • Symptoms include vomiting, seizures, hyperactivity, irritability, and brain damage.
  • PKU homozygotes lack phenylalanine hydroxylase, leading to low levels of dopamine.
  • A phenylalanine-restricted diet can reduce the development of intellectual disability.
• Development of bird song:
  • Sensory phase: birds form memories of adult songs they hear, which guide the development of their own singing.
  • Sensorimotor phase: juvenile male birds develop their own songs through vocalizations and auditory feedback.
  • Most songbird species are age-limited learners, but some are open-ended learners.