Download Lecture 6

Review
Evidence in favor of evolution by natural
selection:
1. Existence and pattern of the fossil record.
2. Homology.
3. Universality of genetic code.
4. Analogy with plant and animal breeding.
5. Direct observation.
6? Adaptations?
-Evolutionary approach to brain, mind
and behavior
-Proximate vs. ultimate
-Mind is specialized
-Mind is not a blank slate (language,
face recognition, sexual desire, mate
choice, parental solicitude…
-Human nature causes culture; it is not
caused by culture: universals.
-Natural selection occurs when
replicating entities have high copying
fidelity relative to their differential
rates of replication.
-Natural (and sexual) selection builds
adaptations that are:
built of existing variation (mutations).
often formed slowly
often formed cumulatively
specialized
costly
may be out of date
-Natural (and sexual) selection builds
adaptations that are good for:
The species?
The group?
The individual?
The gene?
S SS S
SS S S
S SS S
A A A
A AA A
AAA A
SAS S
S AA
A SSA
S SS S
SS S S
S SS S
S
SELFISH MIGRANTS CAN
INFECT A GROUPS
A A A
A AA A
AAA A
S
AND CONVERT THEM
INTO MIXED GROUPS
SAS S
S AA
A SSA
S SS S
SS S S
S SS S
S
SELFISH MIGRANTS CAN
INFECT A GROUPS
A A A
A AA A
AAA A
S
AND CONVERT THEM
INTO MIXED GROUPS
WHICH BECOME PURE
SELFISH GROUPS
SAS S
S AA
A SSA
WHICH TEND TO
GO EXTINCT
S SS S
SS S S
S SS S
S
SELFISH MIGRANTS CAN
INFECT A GROUPS
A A A
A AA A
AAA A
S
AND CONVERT THEM
INTO MIXED GROUPS
WHICH BECOME PURE
SELFISH GROUPS
SAS S
S AA
A SSA
frequency
Evolution by Natural Selection tends to make the
mean phenotype converge on the optimum.
trait value
Sexual Selection
Type of natural selection.
Selection builds adaptations of all types.
Sexual selection builds adaptations that
increase mating success:
1. more mates
2. better mates
Challenges for ancestral males: quantity.
Challenges for ancestral females: quality.
Likely to produce divergent adaptations:
Two optimal phenotypes
Sex differences parallel those in other
primate species.
Facultative adaptations: monitor
environmental variation and adjust
phenotype accordingly.
Selection favored genes that produce
the right pattern of environmental
responsiveness
The effects of experience are preprogrammed by natural selection.
Violence:
Genetic fallacy: Traits shaped by
evolution (biology) are fixed and
inflexible.
Oh really?!?
What about facultative traits?
Norm of reaction tells you how to
change the trait.
Two nature/nurture questions!
1.Why is my skin this color?
causes of development
(interaction)
2. Why do people differ in skin color?
causes of variation
(partition the variance)
If we want to know how heritable a trait
is…
h2 = Vg/Vp, thus
h2 = Vg/(Vg+Ve)
h2 varies from 0 to 1.
Selection is more effective when
heritability is significant; but selection
typically reduces heritability as it works.
Heritability of facultative traits?
Relatively low because of response to
environment.
But obviously designed by selection!
Nature/nurture is misleading!
Mendel’s hypothesis about the stuff
of heredity:
1. Particles, not fluids (genes).
2. Adults have a double dose of
particles (diploid adults).
3. Adults give only half of their double
dose to each offspring (haploid
gametes).
4. Some particles have stronger
effects than others (dominance).
Gene expression: How genes
specify the recipes for proteins
Genetic variation and phenotypic variation
Naturalistic fallacy: what’s natural is
good.
Oh really!?!
tsunamis, disease, aging and
death…
Understanding is not rationalizing.
In the case of facultative traits
understanding points the way to
change.