Chapter 2 Slides

Download Report

Transcript Chapter 2 Slides

Chapter 2
Evolution, Genetics, and
Thinking about the Biology of
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
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 Dualism
Problem 1: Brain damage
has an impact on psychological 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
FIGURE 2.1 Asomatognosia typically
involves damage to the right parietal
Problems of Traditional
Dichotomies: Mind-Brain Dualism
Problem 2: Chimps show psychological (i.e.,
“human”) abilities. For example: Gallup’s
research on chimp self-awareness
Chimps spontaneously groom themselves in
Chimps examine and touch red mark on their
own face seen in mirror
Problems of Traditional
Dichotomies: Nature-or-Nurture
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
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 works)
Darwin presented 3 kinds of evidence
Darwin argued that evolution occurs
through natural selection
Human Evolution: Evidence
for Evolution
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
FIGURE 2.4 Four kinds of evidence
supporting the theory that species
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
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
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
Course of Human Evolution
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.
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 existence
Thinking about Human
Evolution Continued
Evolution does not necessarily result in
perfect design
Not all existing behaviors or structures are
Spandrels—incidental 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
Analogous structures – similar structures
without a common origin
Convergent evolution – the evolution of
similar solutions to the same
environmental demands by unrelated
Evolution of the Human Brain
There is no relationship between brain size
and intelligence
Brain size is generally correlated with body
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
Evolution of the Human Brain
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
Evolutionary Psychology:
Mate Bonding
Most species mate promiscuously
Most mammals form polygynous mating
Humans generally form monogamous bonds
May be adaptive in allowing more attention to
survival of children
Thinking about Evolutionary
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
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 truebreeding lines of pea plants
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
Mendel’s Experiments
True-breeding lines
White (ww)
Brown (BB)
Brown was the dominant trait, appearing in all
of the first generation offspring (Bw)
Mendel’s Experiments
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)
FIGURE 2.15 How Mendel’s
theory accounts for the results of
his experiment on the inheritance
of seed color in pea plants.
Mendel’s Experiments
• Each inherited factor is a gene
• Two genes that control the same trait are
called alleles
• Homozygous – 2 identical alleles (BB,
• 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
• 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 present
• Mitosis – a form of cell division that
yields daughter cells that have 23 pairs
of chromosomes
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
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
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
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
Mechanism of gene expression
Strand of DNA unravels
Messenger RNA (mRNA) synthesized from DNA
mRNA leaves nucleus and attaches to ribosome
in the cell’s 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 expressed
 Epigenetics: the pattern of actual gene expression,
vs. the genes possessed, is most important
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
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
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
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 SingleGene 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 speech
Adult male canaries grow new neurons each
spring: an early discovery of adult
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 IQs 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
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