Anthro 5 – Intro to Physical Anthropology 9/22/2011 10:50:00 AM
I. Class Logistics
a. Class website: www.gauchospace.ucsb.edu
i. Syllabus, lectures, announcements, assignments, links
b. remember to register i-clicker online (gauchospace)
c. homework
i. ideally read chapters ahead
ii. problem sets graded fairly easily
II. The Central Problem of Biology
a. Adaptation: why are organisms so well adjusted to their
circumstances?
i. Camouflage: animals eat other animals; camouflage is used
to protect and blend
b. life is:
i. organized, complex, adjusted to its circumstances, reproduced
ii. why is life all of these things?
1. the process that creates it; evolution by natural
selection: Darwin and Wallace published 1858
a. borrowed 1-3 of 6 step argument from Thomas
Malthus; founder of demography: study of
populations
b. step 1: reproduction is exponential (rapidly
increases over time)
i. not 2, 4, 6, 8, 10 but 2, 4, 8, 16, 32
ii. ex: elephants; begin to reproduce at 30;
have 1 offspring per decade until age of 90;
therefore each pair has 6 offspring
9,000,000 per pair after 750 years
c. step 2: numbers of organisms tend to be
relatively stable in nature
d. step 3: many individuals must fail to reproduce
e. step 4: individuals with advantageous traits are
more likely to survive and reproduce (natural
selection)
f. step 5: offspring resemble their parents
i. successful parents pass on advantageous traits; unsuccessful parents don’t pass on
traits
g. step 6: advantageous traits become more
common over the generations
i. ex: bill shape in Darwin’s finches; climate
affects composition of “seed bank” different
shaped bills better suited to seed bank
become passed down traits in Galapagos
finches climate shifts ultimately changed
bill shape
2. natural selection is the unremitting engine of
biological design: EXPLAINS WHY
a. life is organized, complex, adapted to its
circumstances, and able to reproduce
b. our own species (and all others) has unique
configurations of traits it does
3. limits to kinds of advantageous traits selection can
spread?
a. Yes; traits must be transmitted from parent to
offspring, or genetically
b. Trait must justify its cause vs. cost cause for
the trait in an organism must be of greater worth
than the cost
4. natural selection builds
a. adaptations
b. selects the most effective genetics variants in
each generation Anthro 5 – Intro to Physical Anthropology 9/22/2011 10:50:00 AM
I. evolution by natural selection
a. reproduction has the potential to be exponential
b. almost never is exponential in the real world
c. only way it could fall short of exponential is if individuals fail to
achieve reproductive potential
d. reproductive success is nonrandom with respect to traits
e. offspring resemble their parents
f. traits that foster reproductive success will accumulate in the
population
g. NATURAL SELECTION: differential reproduction of heritable traits
because of a better fit with the environment
II. what determines whether a trait is advantageous?
a. The environment; nature
b. Natural selections sorts available alternatives in population and
holds whatever traits work
c. Advantageous trait: any trait that promotes reproduction
i. “survival of the fittest”; survival is a means to an end, not an
end in itself
1. ex: A wants to live as long as possible, but B wants to
live to but will compromise life to promote offspring
evolution occurs and A will all be dead while there will
be descendants of B
III. designing organisms
a. natural selection designs organisms therefore designs them
for goal of reproduction
b. adaptations: traits that have been preserved by selection
because they aided reproduction
i. why past tense?
1. These traits obviously aided organisms in the
past, but we’re still waiting to find out if they
meet challenges (aid organisms) of the present
and future
ii. many kinds of creatures due to different environments
a. traits that work in one environment may fail
in other environments b. ex: whale (water animal) versus caribou
(land animal)
iii. selection IS NOT an engineer, but IS a tinkerer
a. tinkerer: a person skilled in various modes
of mechanical work
b. selection can’t create new alternatives; only
chooses among available alternatives
(mutation)
iv. homology: the way evolution recycles old elements to
convert them to new elements (ex: forelimb of frogs,
birds, cats, and humans are all very similar)
a. peel back muscle and skin of whale flipper
find an arm
v. *NOTE* natural selection best described as: the
selective retention of specific alternatives in a
population
vi. precision of adaptation
a. how can selection (differential reproduction)
achieve such perfection?
b. My parents reproduced, their parents
reproduced, ancestry continues back and
back we’re inevitably the descendants of
the “winners” since the beginning of time
vii. any limits to kinds of advantageous traits selection can
spread?
a. Every trait has associated costs; trait must
produce net positive reproductive effects
(benefit > cost), otherwise selection won’t
favor it
b. A trait must be transmitted reliably form
parent to offspring; otherwise selection
won’t spread it (e.g. genetically based
traits)
IV. science starts with observations
b. Mendel’s results: bred pure strains of wrinkled and round
together c. F1: Wrinkled x round; offspring were all round; hence, no
blending
d. F2: takes round offspring round x round
o ¾ round: ¼ wrinkled
d. science checks to see if results are
replicable; Mendel regularly got the same
results
1. Mendel’s model
a. Particles, not fluids (genes)
b. Adults have a double dose of particles
(diploid adults)
c. Adults give only half of their double dose to
each offspring (haploid gametes)
d. Some particles have stronger effects than
others (dominance)
F1 hybrid (round) x pure wrinkled (do it yourself)
o Ss x ss 50% wrinkled, 50% round
Genotype: the genes themselves (smooth vs. wrinkly)
Phenotype: the outward expression of those genes
Allele: variant of a gene, for example: wrinkled allele
and round allele of the seed-shape gene; alternative
versions of the same gene
Homozygous: two matching alleles (SS and ss)
Heterozygous: two different alleles
Recessive allele: expressed only when homozygous
Dominant allele: expressed even when heterozygous
Two parents are homozygous for different versions of a trait (AA and aa).
Assuming the trait exhibits complete dominance, their offspring:
All display the dominant phenotype
Have a mix of phenotypes 3 dominant for every 1 recessive
Have a mix of genotypes: approximately 3 recessive for every 1
dominant
All homozygous
Will be half homozygotes and half heterozygotes
Chromosome: linear aggregation of genes (mostly in nucleus) Locus (plural loci): place on a chromosome where genes for a
particular trait occur
genes are alleles of each other if they can occur at the same locus
diploidy: each chromosome is paired, with one from mom and one from
dad
loci match, but alleles may not (if heterozygous)
sex cells (gametes) could be formed by simply giving either your
paternal or maternal chromosome to each gamete
gamete formation involves recombination (crossing over)
exchange of genetic material between maternal and paternal
chromosomes
result = increased genotypic diversity; each chromosome has part
maternal matter and part paternal matter; the other chromosome
of the diploid is the compliment of the first chromosome (matching)
first chromosome 75% mom 25% dad; second chromosome 75%
dad 25% mom Anthro 5 – Molecular Genetics 9/22/2011 10:50:00 AM
Goals
Understand structure of genes
Understand how this structure allows them to make precise copies
Understand how this structure allows them to shape phenotypes
Gene structure has three elements
Phosphates (invariant)
Sugars (invariant)
Bases (variable)
Base pairing rules follow from different types of electron bonds
Always has phosphate, sugar, base *on both sides*
A T (double bond)
C G (triple bond)
DNA will always be able to make perfect copies of itself
o Zip down the middle; knows what’s missing/what needs to be
made based on the A/T/C/G patterns
Therefore, base pairing rules allow perfect DNA replication
o When reproduce, body doesn’t give YOUR genes to offspring,
but gives REPLICAS of your genes made by base pairing rules
Humans are diploid; this means that:
In the DNA, for every sugar molecule, there is a linked phosphate
molecule
For every base in the DNA structure, there is a matching pair (A/T
and C/G)
For every trio of bases on the mRNA, there is a complementary trio
on the tRNA
In each cell, there is one of each chromosome
For each chromosome, we receive a copy from our mother and a
copy from our father
The same kinds of rules allow DNA to serve as a template for phenotypic
instructions; called gene expression
gene expression: how genes specify the recipes for proteins
tRNA: transfer RNA
mRNA: messenger RNA
o RNA vs. DNA
RNA is single stranded
DNA is double stranded Both use 4 bases, but 1 base is different; DNA uses T
while RNA uses U
Ribosome: searches for three successive bases on RNA strands (if
one side has AGG, ribosome looks for UCC to match)
o Each triplet of three bases represents an amino acid
Genetic and phenotypic variation: point mutations
DNA sequence variation in a gene can change the protein produced
by the genetic code
Tying back to evolution: better, more successful genetic strands get
passed on to offspring
Prerequisites for natural selection
1. Heritable 2. Variation that is 3. Associated with differential
reproduction
mutations provide supply of new heritable variation
some variants work better than others and get passed to more
offspring
QUESTION: Why might a particular point mutation be “invisible” to
natural selection?
Selection rejects all mutations because they are copying errors
Point mutations only affect ribosomes
Some codons code for more than one amino acid
Some amino acids can be specified by several different codons
None of the above
QUESTION: mutations
Are errors in gene copying
Provide the raw material for evolution
Create new alleles
Are sometimes “invisible” to selection
All of the above
o Mutations are random with respect to the direction of
adaptation
o Mutations create competing evolutionary units
o Thus, evolution by natural selection is a two-step process
Production (by mutation) of random alternatives
(alleles, and the proteins they specify); sickle cell
example The highly non-random sorting of these alternatives by
natural selection
What is selection’s criterion?
o The ability of the allele to get into the next
generation Genotype – Environment Relationships 9/22/2011 10:50:00 AM
Gene action
Useful to recognize two types of gene action
o Obligate: resist environmental interference
Difficult to find
Obligate variation can be either
o Discrete: just two or a few values
ex: height of Mendel’s peas
o Continuous: many values with no obvious gaps
in the distribution
Ex: height in humans
o Facultative: monitor environmental variation and adjust
phenotype accordingly
Touch-stone example: sun tanning
o Your genes don’t change when you suntan, but
your phenotype does
o Changes by rules coded for in the genes
o How does sun tanning work?
Rate of melanin synthesis (which is a
protein) increased with more UVb exposure
UVb has multiple effects on the body
o + necessary for synthesis of vitamin D
o - causes skin cancer
too little UVb = vitamin D deficiency
too much = skin cancer
o What do we do to get the right about?
Block UVb when there’s too much and let
more in when there’s less
Melanin is a narrow-range, specific UVb
blocker
Produce more or less melanin depending on
which risk is greater = sun tanning
Relative risks vary with latitude, so
populations at different latitudes differ in
baseline (natal) rates of melanin synthesis o UVb also varies with the season, so relative risks
(cancer and vitamin D decifiency) are not
constant
Therefore, facultative adjustment is needed
o QUESTION: a sun tanning adaptation
Depends on seasonal genetic changes
Involves a link between melanin synthesis
and exposure to sunlight
Has been designed by selection because
relative risks change over an annual cycle
Involves a phenotypic response to an
environmental variable
All of the above are true except A
Facultative adaptations are genetically programmed
response patterns built by selection
o Like all adaptations they serve reproductive
success
o Nature wrote the rules for how nurture works
Facultative adaptations versus susceptibilities:
o Sun tanning versus sun burning
Spending all winter inside, then going on
spring break very low UVb exposure to
very high UVb exposure quickly
Turn the thermostat up 10 degrees in a
crowded lecture hall various responses:
sweating, take off sweater, etc.; turn the
thermostat up 100 degrees leads to
changes in phenotypes
o Programmed response versus a failure to respond
o Sweating versus spontaneous combustion
o Facultative traits operate over historical range of
variation
Another example: mate guarding in soapberry bugs
o Males engage in mate guarding: after reproducing
with female, they leave reproductive organ inside
her Benefit: other males can’t inseminate “your”
female; male aiming to fertilize as many
eggs as possible staying inside = less
competition between other males
Cost: there are other females out there, so
if the male is attached to one female, he
can’t inseminate other female bugs
Facultative adaptations are genetically programmed
response patterns built by selection
o Track the environment
o Some facultative traits are irreversible
o Some depend on internal environments
o Some depend on sex (male/female)
QUESTION: Pick the true phrase.
o Obligate traits are always discrete
o High levels of mate guarding would always be
adaptive
o Sun tanning is not an adaptation
o Selection generally favors obligate traits
o None of the above
Nature versus Nurture
nature
o in the genes
o innate
o instinctive
o fixed and inflexible
nurture
o from experience
o learned
o environmental
o flexible
two questions:
o What causes sexual orientation?
This issue is development What combination of genes, fetal environments,
nutrition, peer experiences… led to the phenotype we
see?
These interactions may be preprogrammed (ex: sun
tanning)
Just focused on one individual
o What explains individual differences in sexual
orientation?
Question about why there is variation in a population
People differ in both the genes they carry and in the
environments they have experienced
A group of individuals in population why aren’t we all
the same?
Vp is the phenotypic variation in a trait
“variance” in the statistical measure of variation
we can “partition the variance”
o How much of the phenotypic difference between
individuals:
is associated with the fact that they have different
genes?
And how much is associated with the fact they have
different experiences?
Phenotypic variance (Vp) has two components: Vg and Ve
o Vg is the fraction of phenotypic variance that is associated
with individuals having different genes affecting the trait
o Ve is the fraction of phenotypic variance that is associated
with individuals having different experiences affecting the
traits
o Vp = Vg + Ve
Phenotypic variation is the sum of:
o Underlying genetic variation
o +
o the effects of different environments on the
expression of those genes
Heritability: (h^2) the proportion of total phenotypic variance that
is due to the fact that individuals have different genes o h^2 = Vg/Vp
o therefore:
o h^2 = Vg/(Vg+Ve)
o h^2 varies from 0 to 1
o what kinds of traits have low (or high) heritability?
Low what if Vg were zero?
o No genetic variation; very common because
selection gets rid of the unfavorable alleles ay
trait where we’re all homozygous for the same
gene
Ex: we all have two eyes; in humans there
seems to be no genetic variation associated
with the number of eyes (eye number has
heritability of 0)
Low what if Ve were large?
o Ex: what language you speak
o All phenotypic variance seems to be
environmental
o No genes for mandarin vs. Spanish
Speak a language based on how you’re
raised at home
High what is vg were large (compared to Ve)?
o Ex: blood type
o No Ve; all Vp is the consequence of Vg
o Hence h^2 = 1
o Selection is more effective when heritability is significantly
greater than 0
Selection evaluates phenotypes: some reproduce at
higher rates than others passing on the genes that
built those better phenotypes as long as there are
genetic differences between better and worse
phenotypes
As long as heritability > 0
o Selection is more effective when heritability is significant
What happens as selection operates? it reduces
genetic variance therefore reduces heritability “selection uses up heritability” (new mutations can
reprovision it)
Summary
Mutation can be obligate (discrete or continuous) or facultative
An individual’s phenotype is the result of thousands of gene-
environment interactions
But the phenotypic variation in any population of individuals can be
divided into a fraction that is associated with due to genetic
differences and a fraction that is associated with environment
differences
QUESTION: Which of these is correct?
All genes are made out of RNA
All genes have fixed and invariant effects on the phenotype
Genes tend to mutate in the direction of higher fitness
Eye color has high heritability
None of the above is true Homosexuality and Heritability 9/22/2011 10:50:00 AM
Why hasn’t selection eliminated male homosexuality? (What explains the
variation in sexual orientation?)
Incidence (frequency)?
o At least 2% of men and 1% of women
o Too frequent to be due to mutation
o Selection must have increased the frequency of the relevant
genes
Purely environmental, not caused by genes?
o No, significantly heritable ~ 0.5
The h^2 of male sexual orientation is approximately 0.5
What does that mean?
o Nothing about development
o Nothing about what causes an individual’s sexual
orientation
o Half the variability in sexual orientation in the
population is due to the fact that individuals have
different genes
How do we know the heritability is about 0.5?
o Twin studies:
o How likely is that the twin of a homosexual is also
homosexual?
o Does that differ depending on whether the twins
are monozygotic (genetically identical) or
dizygotic?
Purely environmental, not caused by genes? NO
significantly heritable ~0.5
Does not reduce fitness? Yes, it does. (gay men have
1/10 the reproduction abilities of straight men)
Favored by kin selection? No, gay men do not
systematically aid kin (more than straight men)
Sexually antagonistic genes? Research suggests that a
gene on the X-chromosome is associated with
homosexuality
o What is a sexually antagonistic gene?
A gene with opposite fitness effects in the
two sexes Autosomal, or sex linked? Lower barrier to
x-linked sexually antagonistic genes
Dean Hamer’s research
Pedigree studies: how is gayness distributed in families?
o Can look at pedigree studies to see significant heritability of
homosexuality through carrier women, etc.
Concordant brother studies: what genes do gay brothers share?
Suggests a gene on the X-chromosome that predisposes male
homosexuality
Camperio-ciani et. Al.
Is there any evidence for a sexually antagonistic X-chromosome
gene?
How would you look for it? What patterns would you expect to see?
o In male relatives?
More gay men among matrilateral relatives
o In female relatives?
Higher fitness among female matrilateral relatives
(fitness = reproductive success)
o Straight men won’t show either of these patterns ^
Why is it interesting that the relevant gene is on the X-
chromosome?
o Mutations could cause any phenotypic effect… but will
selection favor them?
For a sexually antagonistic gene, the benefits in sex 1
must outweigh the costs in sex 2
But an X-chromosome gene must raise female fitness
only half as much as it lowers male fitness in order to
produce a net benefit
Environmental effects? Heritability = 0.5, so environmentality = 0.5
“older brother effect”
men with more older brothers are more likely to be gay; not older
sisters; not older step-brothers, not older half-brothers related only
through the father
only older male siblings who shared the same uterus (not a
socialization effect) 33% increase
how might such a “uterine effect” operate? o Y-chromosome
o They produce proteins (from genes coded on his Y) that are
foreign to his mother’s body
o She will produce antibodies (immune system defenses)
against these y-derived proteins
o More sons = more anti-y antibodies
o These maternally produced anti-y antibodies might interfere
with the y-derived proteins of her subsequent sons during
their fetal development
o This maternal interference could disrupt the male-typical
traits that the fetus’ y-derived proteins are trying to produce
SUMMARY: At least two factors (one genetic and one environmental)
contribute to phenotypic variation in male sexual orientation
A gene on the X-chromosome (Xq28) 14%
A uterine influence of older brothers 8%
These two factors only explain about 22% of the variance
78% of variance still unexplained
QUESTION: What is true about male homosexuality?
It has significant heritability
It can be explained by mutation alone
Homosexuals have normal levels of reproductive success
There are no known genes associated with it
None of the above
QUESTION: there is evidence that male homosexuality:
is purely environmental
is associated with a gene or genes on the x-chromosome
may produce fitness benefits in females
b and c are both correct
none of the above is correct
facultative effect: susceptibility Microevolution and Macroevolution 9/22/2011 10:50:00 AM
QUESTION: selection
Causes changes in allele frequency
Produces favorable new mutations
Always favors what is good for the species
Will be efficient when heritability is low
None of the above
Microevolution: generation by generation changes in gene frequency;
happens in ecological time (time we live by)
Macroevolution: large scale changes in species over geological time
(hundreds and hundreds of years)
NOTE: macroevolution is caused by generations and generations of
microevolution
Uniformitarianism: the processes that shape the world are always
the same (ex: gravity)
o Scientific theories are uniformitarian
o Hence, microevolution causes macroevolution
o NOT the idea that the world is always the same
Gradualism: the idea that the changes that are incorporated over
evolutionary time are small changes
o Mutations of small effect are more likely to be helpful than
mutations of large effect
o Why? microscope analogy
o NOT the idea that evolution is always slow
o Two implications of gradualism:
The formation of complex adaptations
o Ex: the eye
o Selection has no foresight
o No allele will spread unless it confers an
advantage in the present
o So, complex adaptations must be built of small
changes, each of which is beneficial
The formation of new species
How quickly can new adaptations arise?
o That depends on the generation time, the amount of variation
and the strength of selection
o Lizard “seeding” experiment (in textbook?) Take lizards from one island, and experimentally move
them to another island (introduce lizard to new
environment/habitat) in new environment lizards
forced to shift diet
Microevolution = change in allele frequency
Macroevolution? What happens overs millions of years?
New species arise (and others go extinct)
Can microevolution explain macroevolution?
Speciation: where do new species come from?
What is a species?
Defined by reproductive isolation
Members of different species don’t share enough genes (gene
map); they can’t interbreed
All organisms are connected in an unbroken ancestor-descendant
chain, back to the first gene-based life forms
How is that the various descendants become reproductively
isolated?
All living chimps and all living humans share an ancestor why
can’t we breed with chimps?
This is the same as the question: where do new species come from?
o A question about the origins of reproductive isolation
o The simplest explanation is called the allopatric model
o Oval with plots within it; range divided by a physical barrier
Individuals from west can’t breed with individuals from
east
If environment changes and barrier disappears two
types might have evolved to be too different to
interbreed (reproductive isolation)
o Any factor that discourages gene flow can serve in place of
the physical barrier
Ex: ecological separation within the same geographic
range
o QUESTION: pick the true statement
Gradualism implies that macroevolution is always slow
The allopatric model is a uniformitarian model of
speciation New adaptations (like the eye) generally arise from one
big mutation
None of the above
Two lines of evidence suggest that the accumulation of small change can
add up to a species-level difference
Domestic breeds (dogs derives from wolves)
Ring species
o Are ring species a problem for our gradualist theory of
evolution by natural selection?
o If lineages diverge gradually should it be the case that, at
every moment in evolutionary time, some populations are
“right on the cusp” of speciation? YES
If we couldn’t find such situations it would be an
embarrassment for our theory
SUMMARY
Mutations (copying errors) create new alleles
These alleles compete with each other
Most mutations are harmful but those with the smallest phenotypic
effects have the best change of being beneficial
Over evolutionary time selection spreads the most beneficial alleles
This process results in both:
o Complex adaptations such as the eye
o New species
TRUE OR FALSE?
There is evidence that many small-scale (microevolutionary)
changes can add up to a species-level difference
True
False Classification and Phylogeny 9/22/2011 10:50:00 AM
Principle: classification should reflect phylogeny
Classification: clustering organisms in natural groups
o Ex: sharks, oaks, birds, penguins
o Not only do we have these categories, but we have a
hierarchical arrangement
Vertebrates: mammals primates (lemurs, monkeys,
apes), bats, cetaceans; birds swifts, ducks, penguins
Phylogeny: deducing ancestor-descendant relationships
This is what makes the groups “natural”
o But what are the natural groupings?
They could be inferred from overall similarity?
o Problems with that?
o What causes similarity between organisms?
Shared ancestry
Convergence makes distantly related
forms similar (ex: sharks, whales, salmon)
o Is a whale a fish?
No, but what makes you so sure?
o Fin structure built differently
o Nurse their young
Why are those traits important in deciding?
o What are the natural groupings?
The ones created by evolution, of course
Those that share a common ancestor
o But all life shares a common
ancestor…
o QUESTION: the fact that all organisms use DNA
(or RNA) as their hereditary material is evidence
that they are all related:
True
False
Explanation: in principle, every kind of
creature could use a different molecule to
transmit hereditary information
Cladistic classification is based on order speciation
Naturally produces hierarchical groups Primitive versus derived similarities
Primitive: trait present in the common ancestor of the group
Derived: trait evolved since divergence from the common ancestor
QUESTION: Having two eyes is primitive for mammals:
True
False
Primitive versus derived similarities
Pentadactyly (having 5 digits) is primitive for mammals
It should not be used to find natural groups of mammals
o But having one toe is derived for mammals
o So those that have one toe may represent a natural group
How to decide what is primitive and what is derived?
Three methods:
o Fossil record
o Out-group comparison
o Order of appearance in development
Cladistics principle: trait present in the outgroup is primitive
QUESTION: Which is the outgroup?
Humans
Nwm
Owm
Howler monkeys
Lemur
Process can be repeated for other traits (whether phenotypic or genetic)
Not all traits give same answer, but each trait counts as vote for
one grouping arrangement or another
Arrangement that gets the most votes wins: maximum
parsimony
QUESTION: what kinds of traits would be least affected by convergence?
Anatomy
Physiology
Behavior
DNA sequences
All equally affected Studying Adaptations 9/22/2011 10:50:00 AM
Natural selection builds:
Traits that meet the challenges of the environment (adaptation)
By selecting the most effective genetic variants in each generation
QUESTION: adaptations:
Are built from mistakes
Cause an organism to be well adapted to its current environment
Always benefit the survival of the species
Can be convergent in distantly related species
A and d are correct
Studying adaptations
what does this adaptation do?
o Two methods:
Reverse engineering
o Look at something that already exists, wonder
how constructed
o What features would the trait have to have, and
how would they have to be connected?
Ex: bat sonar
High frequency, sampling rate, “send-
receive” technology, exploit Doppler effect,
anti jamming features
o Look at the features, how does it operate?
Planned comparisons
o “the comparative method”
o what organisms are most likely to share traits?
Close relatives
True for individuals, and true for species
You and your parent vs. you and me
Chimps and humans vs. squid and humans
o When closely related forms are similar, this is
NOT news
Doesn’t show much evolution
Not much adaptive change shown
o What if closely related forms DID differ; this IS
news (divergence) o And if distantly related forms are similar is also
news (convergence)
o Both situations indicate adaptive evolutionary
change
o Example: eyes
Divergence: among closely related species
of fish, some species lack eyes
o Selection pressure absent when there
is no light
o prediction: cave dwelling species lack
eyes
Convergence: among distantly related
species of fish, shrimp, crayfish,
salamanders, beetles, crabs, etc. a few
species have evolved eyelessness
o Prediction: distantly related cave
dwelling species have converged on
eyelessness
QUESTION: Eyelessness:
Is cheaper than having eyes
Could be adaptive in some environments
Has evolved multiple times
Occurs in species whole close phylogenetic relatives have eyes
All of the above are true
You can use
The idea that all adaptations have costs
And
The method of planned comparisons to understand the “olfactory”
paper
What is the convergence described in that paper?
QUESTION: in an adaptation evolved in 30 or 40 generations, how would
that bear on the plausibility of gradualism in evolution?
It would show that gradualism is wrong
It would not show that gradualism is wrong; such outcomes are not
incompatible with gradualism Gradualism has nothing to do with the emergence of adaptations
Gradualism is not an evolutionary idea, it is a general principle of all
the sciences
Primitive similarities are intentionally neglected in phylogenetic (cladistic)
classification
Primitive traits are present in the ancestors of the group you are
studying
They are simply the older versions of the trait, hence they occur:
o Earlier in the fossil record
o Earlier in development
o In the out-group
Rates of evolutionary change depend on:
Amount of genetic variance (Vg)
Intensity of selection
Generation time
Mutations create new alleles
Over evolutionary time selection spreads the most beneficial
alleles…
o Based on their mean effects on fitness, averaged over all the
contexts in which they occur
Why do social groups exist?
Why do individuals associate and interact with other members of
their species?
Evolutionarily speaking, is it good for them too?
o Or are they doing it to benefit the group or species as a
whole?
Dynamics of social evolution
In particular, what is the entity that social adaptations are designed
to benefit?
o Gene? Individual? Group? PROB NOT Species? PROB NOT Eco-
system? PROB NOT
Selfishness suggests that selection is not working for the good of
the group as a whole,
o But if it isn’t, how could altruism evolve?
Imagine a mutant gene that causes an altruistic (-+)
trait o What will happen to this gene?
o It gets costs, and gives benefits to competitors
o It will be selected against even though it’s good
for the group/species
QUESTION: simple Darwinian natural selection is expected to favor what
kinds of traits?
Cooperative only
Selfish only
Altruistic and cooperative only
Certain traits in all four quadrants (altruistic -+, cooperative ++,
spiteful --, selfish +-
Selfish and cooperative only
Traits that begin with + are beneficial, while traits that begin with – are
detrimental
How do altruistic traits evolve?
Kin selection
o A gene gets into the next generation because it has effects on
phenotypes that cause it (the gene) to get passed to offspring
Effects aren’t limited to the body the gene is sitting in
Example: A gene in Sally can get passed on by
producing phenotypic effects that increase Sally’s
fitness OR it could get passed on by producing
phenotypic effects that decrease Sally’s fitness and
increase the fitness of other individuals who carry
the same gene (“fitness swap”)
o What kind of “fitness swap” would yield a net payoff?
c = fitness cost
b = benefit
r = chance that the gene is shared by common descent
if rb>c, the gene gets a net benefit (Hamilton’s Rule)
o example: Say Sally has a full sister; then r=1/2
o say Sally can give her sister 3 fitness unites (b=3)
at a cost to herself of 1 fitness unit (c=1)
o is rb>c? is ½(3)>1? YES
o this is the kind of altruism that is favored by kin
selection o kin selection is a model of how evolution works, not a model
of how animal minds work
why aren’t b and c always equal?
What sally gives, her sister gets
o But there are natural asymmetries in: exposure to
danger, need, resources, ability to convert
resources into offspring, age that make b and c
unequal
Many studies support this theory
o There are many questions about proximate
mechanisms
Example: kin recognition, evaluation of b
and c
o But there is very little doubt that the theory is
essentially correct
o Phenotypic altruism vs. genetic selfishness
Any evolutionary viable model for altruism will HAVE TO
take the altruism out of it
One phenotype is nice to another but the underlying
genes get a net benefit
Reciprocity Kin Selection and Recipocrity 9/22/2011 10:50:00 AM
Why do social groups exist?
Why do individuals associate and interact with other members of
their species?
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