Transcript Lecture 02

Chapter 2
Evolution, Genetics, and
Experience
Thinking about the Biology
of Behavior
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From Dichotomies to Relations and
Interactions
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Is it physiological or psychological?
 Descartes
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Is it inherited or is it learned?
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 Is
the “naturenurture” debate
alive today?
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Problems with Traditional
Dichotomies – Mind-brain dualism
 Brain
damage impacts
psychological functioning
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Problems with Traditional
Dichotomies – Nature-or-nurture
“
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A model of the biology of behavior
 All
behavior is the product of
the interaction of three
factors:
Genes
Experience
Perception
of the current
situation
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Thinking about Human Evolution
 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.
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Thinking about Human Evolution
 Evolution
is a tinkerer, not an
architect – results are not perfect.
 Not all existing behaviors or
structures are adaptive.
– incidental non-adaptive byproducts (such as the human belly
button)
Spandrels
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Thinking about Human Evolution

Not all existing adaptive characteristics
evolved to perform their current function.
– evolved to do one thing, but now
do something else (such as bird wings)
 Exaptions

Similarities among species do not
necessarily mean that the species have
common origins.
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Thinking about Human Evolution
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
enivironmental demands by unrelated
species

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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.
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Evolution of the Human Brain
 Brain
stem regulates reflex activities
that are critical for survival.
 Cerebrum is involved in complex
adaptive processes such as learning,
perception, and motivation.
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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.
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Fundamental Genetics
 Dichotomous
traits
 True-breeding
lines
 Mendel
studied dichotomous traits in
true-breeding lines of pea plants
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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.
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Mendel’s Experiments
 True-breeding
lines
White
(ww)
Brown (BB)
 Brown
was the dominant trait,
appearing in all of the 1st generation
offspring (Bw)
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Mendel’s Experiments
–
 Genotype –
 Phenotype
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Mendel’s Experiments
 gene
 alleles
 Homozygous
 Heterozygous
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Chromosomes, Reproduction, and
Linkage
Genes
 Chromosomes
 Meiosis

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Chromosomes, Reproduction, and
Linkage
Gametes, eggs and sperm, 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

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Chromosomes, Reproduction, and
Linkage
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”

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Sex Chromosomes and SexLinked 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
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The Interaction of Genetic Factors
and Experience
 Ontogeny –
 Phylogeny –
 Ontogenetic development
is a product
of gene-experience
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