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Thinking about the Biology of Behavior


Chapter 2 Evolution, Genetics, and Experience Thinking about the Biology of Behavior * ... – PowerPoint PPT presentation

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Title: Thinking about the Biology of Behavior

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

From Dichotomies to Relations and Interactions
  • 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

Is It Physiological or Psychological?
  • 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 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

Problems of Traditional Dichotomies Mind-Brain
  • Problem 1 Brain damage
  • has an impact on psycho-logical functioning.
    Example Oliver Sackss case study of a man with
  • Deficiency in awareness
  • of parts of ones own body
  • Due to damage to the
  • right parietal lobe

FIGURE 2.1 Asomatognosia typically involves
damage to the right parietal lobe.
Problems of Traditional Dichotomies Mind-Brain
  • Problem 2 Chimps show psychological (i.e.,
    human) abilities. For example Gallups
    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
  • Many factors have an impact on behavior other
    than genetics (nature) or learning (nurture)
  • Nurture now encompasses learning and
  • 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

FIGURE 2.3 A schematic illustration of the way in
which many biopsychologists think about the
biology of behavior.
Human Evolution
  • While Darwin was not the first to propose that
    species evolve, he was the first to compile
    supporting evidence (and to suggest how evolution
  • Darwin presented 3 kinds of evidence
  • Darwin argued that evolution occurs through
    natural selection

Human Evolution Evidence for Evolution
  • Darwins 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

FIGURE 2.4 Four kinds of evidence supporting the
theory that species evolve.
Evolution and Behavior
  • Just as physical features can contribute to
    fitness, so do behaviors
  • Some are obviousthe ability to find food, avoid
    predation, etc.
  • Some are less obvioussocial dominance and
    courtship displays

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

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.
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
    mothers body
  • Humans emerge from the order primates

Course of Human Evolution Continued
  • 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

FIGURE 2.9 A taxonomy of the human species.
FIGURE 2.10 The remarkably complete skull of a
3-year-old Australopithecus girl. The fossil is
3.3 million years old.
FIGURE 2.12 Vertebrate evolution.
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

Thinking about Human Evolution Continued
  • Evolution does not necessarily result in perfect
  • Not all existing behaviors or structures are
  • Spandrelsincidental nonadaptive by-products
    (such as the human belly button)

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

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

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

FIGURE 2.13 The brains of animals of different
evolutionary ages. Cerebrums are shown in
yellow brainstems are shown in purple.
Evolution of the Human Brain Continued
  • The human brain has increased in size during
  • Most of the increase in size has occurred in the
  • Increased convolutions in the cerebrum have
    served to increase the volume of the cerebral

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

Thinking about Evolutionary Psychology
  • Current aspects of mate bonding in humans appear
    to be predicted by evolutionary theory.
  • 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
  • Men are more likely than women to commit adultery

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

Mendels 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

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

Mendels 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

FIGURE 2.15 How Mendels theory accounts for the
results of his experiment on the inheritance of
seed color in pea plants.
Mendels Experiments Continued
  • Each inherited factor is a gene
  • Two genes that control the same trait are called
  • Homozygous 2 identical alleles (BB, ww)
  • Heterozygous 2 different alleles (Bw)

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

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
  • Mitosis a form of cell division that yields
    daughter cells that have 23 pairs of chromosomes

Chromosomes Reproduction and Recombination
  • 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

Meiosis versus Mitosis
Crossing Over Increases Genetic Diversity
Meiosis Simple Story
Meiosis Actual Story
Chromosomes Structure and Replication
  • 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

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.
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

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

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
  • Epigenetics the pattern of actual gene
    expression, vs. the genes possessed, is most
  • patterns of gene expression appear to be heritable

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.
Mitochondrial DNA
  • 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

Mitochondrial DNA
  • 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
  • spread around the world

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

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

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

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

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

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
  • Adult male canaries grow new neurons each spring
    an early discovery of adult neurogenesis

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
  • Example Correlations of the IQ s of identical
    twins whether raised together or apart is larger
    than that of fraternal twins raised together

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