Thinking about the Biology of Behavior Chapter 2 Evolution, Genetics, and Experience 1

There is a tendency to think in simple dichotomies when explaining behavior: Is it physiological or psychological? Is it inherited or is it learned? Both questions are common, yet misguided From Dichotomies to Relations and Interactions 2

Cartesian dualism: Descartes argued that the universe consists of two elements Physical matter Human mind (soul, self, or spirit) Cartesian dualism viewed the mind and brain as separate entities Is It Physiological or Psychological? 3

Is It Inherited or Is It Learned? The “nature-nurture” issue Watson, a behaviorist, believed that all behavior was the product of learning (nurture) Ethology, the study of animal behavior in the wild, focuses on instinctive (nature) behaviors 4

Problem 1: Brain damage has an impact on psycho- logical functioning. Example: Oliver Sacks’s case study of a man with asomatognosia Deficiency in awareness of parts of one’s own body Due to damage to the right parietal lobe Problems of Traditional Dichotomies: Mind-Brain Dualism 5

FIGURE 2.1 Asomatognosia typically involves damage to the right parietal lobe. 6

Problem 2: Chimps show psychological (i.e., “human”) abilities. For example: Gallup’s research on chimp self-awareness Chimps spontaneously groom themselves in mirror Chimps examine and touch red mark on their own face seen in mirror Problems of Traditional Dichotomies: Mind-Brain Dualism 7

Many factors have an impact on behavior other than genetics (nature) or learning (nurture) “Nurture” now encompasses learning and environment While it is generally accepted that behavior is a product of nature and nurture, many still ask how much is determined by each, but genetic and experiential factors do not merely combine in an additive fashion interactionism Problems of Traditional Dichotomies: Nature-or-Nurture 8

FIGURE 2.3 A schematic illustration of the way in which many biopsychologists think about the biology of behavior. 9

While Darwin was not the first to propose that species evolve, he was the first to compile supporting evidence (and to suggest how evolution works) Darwin presented 3 kinds of evidence Darwin argued that evolution occurs through natural selection Human Evolution 10

Darwin’s evidence Fossil evidence of evolution Structural similarities among living species suggesting common ancestors Impact of selective breeding Direct observation of evolution in progress: Grant (1991) Finches of the Galapagos islands changed dramatically after a single season of drought Human Evolution: Evidence for Evolution 11

FIGURE 2.4 Four kinds of evidence supporting the theory that species evolve. 12

Evolution and Behavior Just as physical features can contribute to “fitness,” so do behaviors Some are obvious—the ability to find food, avoid predation, etc. Some are less obvious—social dominance and courtship displays 13

Course of Human Evolution Evolution of vertebrates Chordates have dorsal nerve cords Vertebrates are chordates with spinal bones Evolution of amphibians Bony fishes leave the water briefly Advantages include fresh water and new food sources 14

FIGURE 2.6 A recently discovered fossil of a missing evolutionary link is shown on the right, and a reconstruction of the creature is shown on the left. It had scales, teeth, and gills like a fish and primitive wrist and finger bones similar to those of land animals. 15

Course of Human Evolution Continued Evolution of reptiles Lay shell-covered eggs; covered by dry scales Can live far from water Evolution of mammals Develop mammary glands to nurture young Eventually no longer lay eggs: raise young in mother’s body Humans emerge from the order primates 16

Emergence of humankind Humans belong to family hominids, genus Homo First homo species emerged from Australopethicus 2 million years ago Homo sapiens emerged 200,000 years ago Course of Human Evolution Continued 17

FIGURE 2.9 A taxonomy of the human species. 18

FIGURE 2.10 The remarkably complete skull of a 3-year-old Australopithecus girl. The fossil is 3.3 million years old. 19

FIGURE 2.12 Vertebrate evolution. 20

Thinking about Human Evolution Continued Evolution does not proceed in a single line Humans have only been around for a brief period of time Rapid evolutionary changes do occur Fewer than 1% of all known species are still in existence 21

Thinking about Human Evolution Continued Evolution does not necessarily result in perfect design Not all existing behaviors or structures are adaptive Spandrels — incidental nonadaptive by-products (such as the human belly button) 22

Thinking about Human Evolution Continued Not all existing adaptive characteristics evolved to perform their current function Exaptations – evolved to do one thing, but now do something else (such as bird wings ) Similarities among species do not necessarily mean that the species have common origins 23

Thinking about Human Evolution Continued Homologous structures – similar structures due to a common evolutionary origin Analogous structures – similar structures without a common origin Convergent evolution – the evolution of similar solutions to the same environmental demands by unrelated species 24

Evolution of the Human Brain There is no relationship between brain size and intelligence Brain size is generally correlated with body size More informative to look at relative size of different brain regions 25

FIGURE 2.13 The brains of animals of different evolutionary ages. Cerebrums are shown in yellow; brainstems are shown in purple. 26

Evolution of the Human Brain Continued The human brain has increased in size during evolution Most of the increase in size has occurred in the cerebrum Increased convolutions in the cerebrum have served to increase the volume of the cerebral cortex 27

Evolutionary Psychology: Mate Bonding Most species mate promiscuously Most mammals form polygynous mating bonds Humans generally form monogamous bonds May be adaptive in allowing more attention to survival of children 28

Thinking about Evolutionary Psychology Current aspects of mate bonding in humans appear to be predicted by evolutionary theory. Examples: Men tend to value indications of fertility Women tend to value power and earning capacity Physical attractiveness predicts which women bond with men of high status Mate attraction strategies: for women, physical attraction; for men, displaying power and resources Men are more likely than women to commit adultery 29

Fundamental Genetics Dichotomous traits – occur in one form or the other, never in combination True-breeding lines – interbred members always produce offspring with the same trait Mendel studied dichotomous traits in true- breeding lines of pea plants 30

Mendel’s Experiments Crossed a line bred true for brown seeds with one bred true for white First generation offspring all had brown seeds When the first generation were bred, the result was ¾ brown and ¼ white seeds 31

Mendel’s Experiments Continued True-breeding lines White (ww) Brown (BB) Brown was the dominant trait, appearing in all of the first generation offspring (Bw) 32

Mendel’s Experiments Continued Phenotype – observable traits Genotype – traits present in the genes If the dominant trait is present in the genotype (Bw), it will be observed in the phenotype (brown seeds) 33

FIGURE 2.15 How Mendel’s theory accounts for the results of his experiment on the inheritance of seed color in pea plants. 34

Mendel’s Experiments Continued Each inherited factor is a gene Two genes that control the same trait are called alleles Homozygous – 2 identical alleles (BB, ww) Heterozygous – 2 different alleles (Bw) 35

Chromosomes: Reproduction and Recombination Genes are located on chromosomes in the nucleus of each cell Humans have 23 pairs of chromosomes, with an allele on each chromosome Meiosis – a process of cell division that yields cells with just 23 chromosomes 36

Chromosomes: Reproduction and Recombination Gametes, egg cells and sperm cells, are produced by meiosis When egg and sperm combine to form a fertilized egg (zygote), 23 pairs of chromosomes are again present Mitosis – a form of cell division that yields daughter cells that have 23 pairs of chromosomes 37

Chromosomes: Reproduction and Recombination Continued Meiosis leads to diversity as the 23 pairs of chromosomes are randomly sorted into the 2 gametes produced Linkage – the tendency of traits encoded on the same chromosome to be inherited together Crossing over – increases diversity, “shuffles the genetic deck” 38

Meiosis versus Mitosis 39

Crossing Over – Increases Genetic Diversity 40 Meiosis … Simple StoryMeiosis … Actual Story

Chromosomes are DNA molecules: double strands of nucleotide bases wrapped around each other A nucleotide on strand 1 always pairs with a particular nucleotide on strand 2 To replicate, the strands unwind; each nucleotide attracts its complementary base, making two DNA molecules identical to the original Chromosomes: Structure and Replication 41

FIGURE 2.18 DNA replication. As the two strands of the original DNA molecule unwind, the nucleotide bases on each strand attract free-floating complementary bases. Once the unwinding is complete, two DNA molecules, each identical to the first, will have been created. 42

Sex Chromosomes and Sex-Linked Traits Sex chromosomes, X and Y, look different and carry different genes Female = XX Male = XY Sex-linked traits – influenced by genes on the sex chromosomes Dominant traits on the X chromosome will be seen more commonly in females, recessive ones in males 43

Genetic Code and Gene Expression Mechanism of gene expression Strand of DNA unravels Messenger RNA (mRNA) synthesized from DNA (transcription) mRNA leaves nucleus and attaches to ribosome in the cell’s cytoplasm Ribosome synthesizes protein according to 3-base sequences (codons) of mRNA (translation) 44

Genetic Code and Gene Expression Continued Regulation of gene expression Enhancers: stretches of DNA that determine whether particular structural genes initiate the synthesis of proteins and at what rate Transcription factors: proteins that bind to DNA and influence the extent to which genes are expressed Epigenetics: the pattern of actual gene expression, vs. the genes possessed, is most important patterns of gene expression appear to be heritable 45

FIGURE 2.19 Gene expression. Transcription of a section of DNA into a complementary strand of messenger RNA is followed by the translation of the messenger RNA strand into a protein. 46

Mitochondrial DNA Mitochondria are the energy-generating structures found in the cytoplasm of all cells Mitochondria have their own DNA Mitochondria were once believed to come from mother, but paternal mitochondrial DNA has been found in one individual 47

Mitochondrial DNA Research interest in mitochondrial DNA  Mitochondrial DNA may be responsible for some disorders  Constant rate of mitochondrial DNA mutation has been used as evolutionary clock to determine, for instance, that hominids evolved in Africa and spread around the world 48

Modern Genetics Modern genetics Human genome project mapped the 3 billion base sequences of human DNA, as well as those of some other species 49

Modern Genetics Continued Humans were found to have only about 25 thousand genes, leading to new discoveries:  Only a small proportion of chromosome segments contain protein-coding genes  Vast regions of DNA were once thought to be inactive evolutionary remnants. However, they are now thought to influence the structural genes  “active nongene DNA” 50

Modern Genetics Continued  microRNA appears to have an expanded role in gene expression, beyond carrying information from the nucleus  Some genes produce more than one protein  alternative splicing of messenger RNA provides a mechanism  Evidence for expression of only one allele of a gene (monoallelic expression) has accumulated in the past few years 51

Behavioral Development: The Interaction of Genetic Factors and Experience Three influential studies Selective breeding of “maze-bright” and “maze-dull” rats Phenylketonuria: a single-gene metabolic disorder Development of birdsong 52

FIGURE 2.21 Selective breeding of maze-bright and maze-dull strains of rats by Tryon (1934). 53

FIGURE 2.22 Maze-dull rats did not make significantly more errors than maze-bright rats when both groups were reared in an enriched environment. (Adapted from Cooper & Zubek, 1958.) 54

Phenylketonura: A Single- Gene Metabolic Disorder Due to single mutant recessive gene Special diet during critical period of development lessens mental retardation An example of interaction of genetics and environment 55

Development of Birdsong Young males must hear their species’ songs during critical period, or they develop abnormal songs Young male canaries have left-side neurological dominance for song, like human left dominance for speech Adult male canaries grow new neurons each spring: an early discovery of adult neurogenesis 56

The Genetics of Human Psychological Differences Minnesota study of twins reared apart showed that identical twins are more similar to each other than fraternal twins on all psychological dimensions Example: Correlations of the IQ s of identical twins whether raised together or apart is larger than that of fraternal twins raised together 57

FIGURE 2.25 The correlations of the intelligence quotients (IQs) of identical and fraternal twins, reared together or apart (see Bouchard, 1998). 58

Individual Differences Continued Heritability estimates refer to populations, not to individuals cannot be generalized to populations from dissimilar environments Multiplier effect – genetically similar individuals seek out similar environments Turkheimer et al. (2003) – heritability of IQ was near 0 in impoverished twins and near 1 (maximum) in affluent twins 59