Evolu on and Psychology
Exam 1 Study Guide
Introduc on
What three primate species are the closest rela ves of humans?
Gorillas, chimpanzees and bonobos
Explain how tes s size is related to primate ma ng structure.
Mul Male ma ng with one female: Large tes s (therefore because of the tes s larger size sperm
compe on can take place)
Single male ma ng with one female: smaller tes s (instead of sperm compe
physical compe ons, gorillas for example have larger torsos.
on, there would be
If a new primate species were discovered and exhibited a high degree of sexual size dimorphism
in the upper body and had a ma ng structure much like that of gorillas, would we expect tes s
size as a propor on of body weight to be fairly large or fairly small?
The tes s would be small. If the ma ng structure is like gorillas where a single male is ma ng
with a single female, there would therefore be no compe on between sperm. Also because
of the of the size dimorphism (the upper body being larger- as that is the case with gorillas)
that means that males would be compe ng physically as they can’t compete from below the
waist (as their tes s are small).
Of the four great ape species, which has the largest breasts and penis as a propor on of body weight?
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Humans
How do the views of Alfred Russel Wallace relate to those of Charles Darwin when it comes to the
relevance of evolu on by natural selec on for understanding the psychological capaci es of humankind?
They both independently proposed the theory of natural selec on.
Darwin goes on a voyage on the beagle and his notebook records evolu onary ideas (sketched an
evolu onary tree) he then reads an essay by on the principle of popula on by Thomas Malthus which
led him to the insight that he later termed natural selec on.
Wallace was inspired by Darwins voyage therefore Wallace decides to go on a voyage of his own in the
Brazilian rainforest. Wallace develops the theory of natural selec on and sends le er to Darwin
describing it.
Historical and Conceptual Overview
De ne “evolu on.”
Change over me in a popula on— speci cally change in gene frequencies!
What are 4 mechanisms that produce evolu on?
1. Migra on (gene ow)
2. Muta on (new gene c varia on)
3. Gene c Dri (Random Varia on across genera ons)
4. Natural Selec on (di eren al reproduc ve success due to inherited varia on among individuals)
Which one produces the appearance of complex design (adapta ons)?
Natural Selec on: The only known, naturally occurring mechanism that will produce the appearance
of design in organisms
Explain William Paley’s argument for design.
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—Prevailing theory before Darwin
-Special Crea on —The visible evidence of design suggested the presence of a Designer, as argued
most notably by William Daley
Name two thinkers who, prior to Darwin, put forward evolu onary views?
-William Paley
-Erasmus Darwin (Darwins grandfather) — suggested unity of all life via common descent and (posi ve
direc onal) change in species over me. (Di ered from Charles Darwin)
What mechanism for evolu on was suggested by Lamarck?
Embraced evolu on and even posited mechanisms for its occurrent, including the (inheritance of
acquired characteris cs) — Ex: Gira e and how neck gets longer over me to get leaves from the tree
high up
What late 19th century biologist refuted Lamarckism in a series of experiments? How did he do
this?
—August Weismann dis nguishes between germ line and soma in the ow of inherited
informa on, and discredits Lamarckism views of inheritance of acquired characteris cs
-Cut o tails of mice for 20 genera ons and bred them, but were born with tails
What was the importance of Charles Lyell’s book Principles of Geology in the development of the theory
of evolu on?
—Charles Darwin takes the published book of principles of Geology with him on his trip on the beagle.
Darwin makes the idea of deep me plausible! (everyone thought the Earth was young, but the book
proposes Earths age as a lot older). He also sketched an evolu onary tree in his B notebook on
transmuta on of species. He is eventually convinced of branches of descent.
What book by Thomas Malthus in uenced both Darwin and Malthus in origina ng the no on of natural
selec on? What was its key argument? What role does this argument play in natural selec on?
— Thomas Malthus introduced An essay on Principle of Popula on
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—Popula ons will grow faster than the resources needed to sustain them. Popula on will crash and
there will be compe on for resources, be er equipped individuals will survive be er.
On July 1st 1858— A joint paper on the theory is presented to the Linnean Society, Darwin later
publishes on the Origen of Species and introduces Sexual Selec on.
In the 1900— Re-discovery of Mendelian Gene cs
Brie y summarize the major contribu ons to biology in the wake of Darwin made by the following
gures:
William Hamilton: Introduces “Inclusive Fitness Theory” which Is a major re nement of Darwins Original
Theory
— Explains apparently paradoxical cases of organisms behaving in a self less manner (ex: Worker ants
store food/water in their stomach and share it with the sick ants. They also take out diseased/ dead ants
out of the community to keep it healthy and safe.) A re nement to Darwin because Darwin said survival
of the est
George C. Williams: Published Adapta on and Natural Selec on
-Provides criteria for iden fying adapta ons
-Refutes group selec on claims (that behavior can be for the good of the species”
Richard Dawkins: Publishes The Sel sh Gene (gene centric view on life)
-Crystalizes the “gene centric” view of life which organisms are vehicles for the propaga on of the genes
that build them
Rober Trivers— The Parent-o spring rela onship and hw genes can impact human behavior
-Reciprocal Altruism
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E.O Wilson: publishes Sociobiology:The new synthesis,, in uen al synthesis of recent advancements but
controversial because in one chapter that he applied to humans.
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—Darwin stated that The reading of Malthus “at once” led him to the insight that he later termed
natural selec on.
William James: Publishes the Principles of Psychology- strongly in uenced by Darwin, for James, the goal
of psychology was to describe how mental processes help people adapt. Emphasized the role of ins ncts
in human behavior! Cri cized because it describes but does not explain behavior
-He called a en on to the ins nct blindness
What is ins nct blindness, and who rst called a en on to it?
— William James called a en on to the ins nct of blindness. It is the idea that psychologists and
laypeople do not recognize the extraordinary nature of our capaci es because we live in it every day
and it seems natural to us. We do not have the ability to step outside of ourselves and truly appreciate
our abili es. Wanted to call a en on to automa c process that are complicated.
What is ethology?
—It is the study of animal behavior under natural condi ons, informed by natural selec on
(assump on that behavior is adap ve). Unlike behaviorism that is controlled, they observe animals in
their natural habitats and see how their adap ve behaviors are helping them survive.
Konrad Lorenz— found out about imprin ng/ xed ac on pa erns: a more sophis cated treatment of
ins ncts
Be very familiar with Tinbergen’s 4 ques ons—including recognizing examples of each.
1. Causa on: or mechanism, physiology (ex: neural connec ons, hormonal, cellular mechanisms)
that ve rise to the behavior (Proximate)
2. Development: or Ontogeny, how the behavior arises during the process of development/
lifespan, how it changes over me (Proximate)
3. Evolu on: or Phylogeny, how is the behavior con nuous with and di erent from similar
behaviors in other species- including ex nct species from which it might have descended
4. Func on: The role the behavior plays in how the species is adapted to its environment
Useful mnemonic: ABCDEF— Animal behavior, cause, development, Evolu on and Func on
What is the di erence between a proximate and an ul mate explana on of behavior? What kind of
explana on do most psychologists tend to focus on?
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Proximate: Answer “how” ques ons (how do features change, how external/ internal forces cause a
feature— Answered by focusing on individual)
Ul mate explana on: Answer “why” ques ons (ex: what is the reason for or purpose or func on of the
feature. What forces cause a feature to characterize a whole species of organisms. Answered by focusing
on popula ons)
1950s-60s— Rise of cogni ve science and decline of behaviorism in America
-Garcias experiments on condi oned taste aversions- specialized learning mechanism- rats associated
nausea with taste more readily than other senses, discovered that some things are more easily
associated with others, this can also apply to language
-Noam Chomsky cri cized Skinner. Emerging consensus that a few domain- general learning
mechanisms cannot fully account for human behavior. Greater focus on more specialized, biologically
prepared learning mechanisms
70s-80s— sociobiology applied to humans
80s-92— Evolu onary psychology emerges— facilitated by cogni ve psych! — Product of Wilson and
Darwin (but more Wilson
What book is considered the manifesto of contemporary evolu onary psychology? What two
psychologists are considered by many to be the founders, or the conceptual architects, of the eld?
— Mar n Daly and Margo Wilson publish Homicide— landmark applica on of natural selec on
thinking to aggression
What are the major conceptual and methodological di erences between Darwinian anthropology,
evolu onary psychology, and gene-culture coevolu onary theory (see textbook)?
Darwinian anthropology: sociobiology applied to people, means that the assumption that
human behavior is going to adaptive (help reproduce and survive) — culturally
transmitted behaviors are going to be adaptive (like cooking
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—evolutionary psychology: going to focus on trying to understand psychological
adaptations, we are trying to gure out speci c structure of adaptations and that structure
matters— we have to understand the adaptation so once we do the can see that sometimes
environment can change and the adaptive changes (salty taste likeness before very useful
and now its everywhere so not as useful
gene culture coevolutionary theory: we are going to argue that human biology evolves
through genes and we have cultural evolution— how is genetic evolution related to cultural
evolution (can culture evolve that is maladaptive?) — ex: cultural environment where its
common to believe falsehoods because it gets you into the in group also certain dietary food
restrictions from a culture maybe be maladaptive— like if we cant eat cows and there are
many cows in surrounding and your hungr
What is the fundamental di erence between (human) sociobiology and evolu onary psychology?
sociobiologists would generally examine human behavior on the assump on that people maximize
inclusive tness.
Evolu onary psychologists examine human behavior on the assump on that it is the output of
evolved psychological adapta ons, which arose because they used informa on-processing procedures
to solve ancestrally recurring adap ve problems.
The di erence is subtle but important. Although speci c adapta ons arose because they (on average)
increased inclusive tness under ancestral condi ons, execu ng adapta ons is not the same as
maximizing current tness. More on this later.
Evolu on and Natural Selec on
The Design Stance: William Paley gave the best explana on of the Problem of design. (How to explain
the appearance of design among species— extraordinary and clearly non-random, t between
organisms and environment.)
— Natural Theology book analogy: A watch found lying on the ground stands out compared to the
surrounding (therefore we pick it up). The watch serves a par cular purpose (telling me) that
bene ts intelligent beings. It is too complex for it to have been created by chance. If any of its pieces
were a di erent size or shape, then the internal mechanisms would fail. Therefore objects like the one
states must require a designer (a watch maker)
—Darwins theory explains “design aws” an example is blind spot in eye because it is from decent
How did Darwin’s observa ons of nches on the Galapagos Islands help convince him that species had
evolved?
—Special Crea on did not make sense to Darwin. He believed that there was an evolu onary account
for an ancestral bird that had dispersed and had descent with modi ca on, which was more plausible.
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-Organisms produce many more o spring than are required to replace the parents (Malthus)
-Individuals within a popula on show a range of heritable variability across numerous physiological
and behavioral traits (selec ve traits)
-some traits suit one be er to survival and reproduc on that others do
-Successful parents become be er represented among the next genera on.
- Eventually enough chance may accuse to reproduc vely isolate a popula on from other popula ons,
thereby leading to a new species
Explain how evolu on by natural selec on works. What are the three essen al ingredients (or building
blocks) of the process?
-Varia on (copies not exact replicas), Inheritance (replicators make copies of themselves), Di eren al
reproduc on (aka selec on) of the varie es produced, some survive and reproduce be er than
others.
How does design by natural selec on di er from design by engineering?
-Designer: Forward looking, actual goals are represented somewhere, tear down exis ng design and
star ng over, only responds to things the designer consciously knows about
-Natural Selec on: not forward looking, no goals represented, design but not rear down exis ng
design: design is heavily conserved at the popula on level (though not at the prototype level)—
responds to all con ngencies and long term accumula on of small improvements
Describe three major gaps in Darwin’s theory of evolu on by natural selec on as ini ally presented.
— No theory of inheritance: No concept of muta on/ how traits are inherited, the mechanisms which
involves novel varia on. Without it, increases in complexity on a macro evolu onary mescale are
di cult to envision.
— Solu on: Mendelian Gene cs, Watson and Crick
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— The genes eye view: Some replicators (genes) will replicate faster than others. 3 kinds of copying
errors: errors that don’t make a di erence, errors that cause the replicator to decrease its replica on
rate, errors that cause the replicator to increase its replica on. Wide variety of e ects that impact
replica on rate
—Cases of sel ess/altruis c behavior— bene ts others at a cost of the self ex. Bees s nging/ sacri cing
themselves to protect hive
Elaborate characteris cs lacking in obvious func on/ seemingly detrimental to Survival— peacocks
tail!
What is meant by the concept of “the sel sh gene” as described by Dawkins?
Only genes survive to the next genera on— they are true replicators. Your o spring are not exact
copies of you, but their genes are exact copies of yours and your mates.
-Genes survive because they build parts of organisms the right way— in a way that favors their own
reproduc on
-In this sense, we can say that genes are sel sh! - disproves design theory
—When we take a genes eyes view, we view Organisms as machines built by genes to promote genes
reproduc on.
-“An individual organism is a throwaway survival machine for the self-replica ng, coded into which it
contains”
Explain inclusive tness.
Altruism: used genes eye view to conclude that genes can foster their success by promo ng the
reproduc on of copies of itself carried by other individuals.
Inclusive tness: Direct and indirect tness together and it gives you inclusive tness! - helping other
people in the popula on because all have very similar genes.
-inclusive tness (direct (genes build body for more o spring) plus indirect (genes build body and help
others)
Example; alarm calls, helping at the nest
Also called kin selec on- because individuals who are likely to carry the same genes are gene c
rela ves. An allele may spread because it causes its bearer to reproduce on and because it causes its
bearer to help others to reproduce who drelikely to carry the same gene
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- major theore cal reconceptualiza on fo the nature of living thing— old view: All organisms selected
to be completely sel sh. Hamilton shows that designs are built in with altruism in them.
- We share 99 percent of the same genes, however the varia on in the other 1 percent of the genome
allows for the evolu on of kin selec on
Maximiza on of inclusive tness is the purpose and the process of natural selec on— sociobiology
What is Hamilton’s rule? Be prepared to apply it in prac ce.
—when would helping someone pay o for you, from the genes eye view
-We can see evolu onary altruism when rB is greater than C
C= how costly It would be for the helper to help
B= how much of a bene t the recipient would receive
R is the number (so the relatedness) mes B (what they receive) if thats bigger than you (C) then you
should help!
Bene
ng others at the cost of themselves
What is the coe cient of relatedness? Be able to iden fy the coe cient of relatedness for major types
of rela onships (e.g., full siblings, rst cousins).
-r= 0.5— for parents and o spring siblings
r= 0.25—between grandparents and grandchildren (uncles or aunts and nieces or nephews/ half
siblings)
r=0.125— rst cousins
r= 0— step parents and children/ step siblings
What are the three end products of evolu on? Be prepared to iden fy examples of each.
1. Adap ons: inherited and reliably developing characteris cs that emerged because they func oned
to solve recurring ancestral problems, resul ng in greater reproduc ve success
Ex: A fear of snakes might be a psychological adapta on
2. By-products- side e ects of adapta onism, these did not emerge directly by virtue of improving
reproduc ve success (ex: umbilical cord)
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3. Noise- chance varia on, RANDOM EFFECTS- the random shape of an individuals naval is an example
of Noise
What are adapta ons?
Features designed by natural selec on to solve the speci c problems posed by the environments
encountered by ancestral popula ons during the course of that popula ons evolu on.
-not every trait is an adapta on and adapta ons promote inclusive tness
-George C williams
What is group selec on and how did George Williams largely convince biologists that selec on occurs at
the level of the gene and individual rather than the group or species? (Textbook should be useful here)
— group selection: to try to explain altruism (the good of the species) — the birds are
helping at nest and taking one for th
George Williams says it false (want to explain altruism correctly!- William Hamilton and
inclusive tness) - why is altruism happenin
Group selec on: altruis c adapta ons happen for the good of the species
Iden fy and explain two limita ons of the adapta onist method, as noted by George Williams.
environmental mismatch example: coca cola and hamburgers (our preferences for salty
and sweet)-
evolutionary constraints (not every adaptation is optimal). : example: the eye (early
evolution- blind spot because the nerve comes out of rods and codes to penetrate to the
brain) and competing selection forces (selection for bigger brain size, also constraint to
human female pelvic size— if baby's heads brain gets too big then its bad for birth
Provide an example of a human trait that is thought to re ect each limita on. (Not on
)
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the slides, but we discussed some).
(Listed above)
List the three criteria the Williams provided for iden fying an adapta on? What are the requirements for
iden fying an adapta on, according to Tooby and Cosmides?
1. Reliability: regularly develops under normal condi ons
2. Economy: solves adap ve problem at low cost
3. E ciency: performs func on well
Tooby and Cosmides requirements:
1. Has many design features that are improbably well suited for solving an ancestral adap ve problem
2. These proper es are unlikely to have arisen by chance
3. These features are not be er explained as the byproduct of mechanisms designed to solve some
alterna ve adap ve problem or some more inclusive class of adap ve problem
What is (properly) meant by the Environment of Evolu onary Adaptedness (EEA)?
“Environment of evolu onary adaptedness” this is a sta s cal composite of the set of dimensions of
the environment relevant to an organisms ancestral environment. (It is the set of selec on pressures
that shaped an adapta on.
—Environment of evolutionary adaptednes
selection pressures come from environmen
we want to think of the environment where adaptions occurred — adaptations can be
targeted to a speci c time and plac
a set of selection pressures that shapes a particular adaptatio
each adaptation has its own EE
Explain Gould and Lewon n’s cri que of adapta onism?
What is a spandrel?
-A term derived from architecture, here used to mean a by product of natural selec on
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What is a just-so story?
-A plausible account of a traits origin and func on. But one that lacks conceptual rigor and
that makes few if any falsi able predic ons.
-as a result adapta onists are generally much more careful in pro ering hypothesis
Sex and Sexual Selec on
How does the e ect size for sex di erences in human height compare to that for sex di erences in
human strength?
E ect size: a measure of the magnitude of the di erences between 2 groups- o en expressed in
standard devia on units
Cohens D: default e ect size between men/women — the number tells us how far apart the groups
are in SD. Women and Men have Cohens D: 2.0 (MEANS MEN STRONGER THAN WOMEN)
What is sexual selec on? How did Darwin conceive of sexual selec on to be di erent from natural
selec on?
-Darwin: The descent of Man and Selec on in rela on to sex
-A mechanism proposed by Darwin, this focuses on success in ma ng not on survival. Sexual selec on
arises through variance (spread out SD) in ma ng success
Darwin needed a theory that explained the many extravagant traits that seem to reduce survival
(peacock tail, sexual dimorphism)
Iden fy and describe two kinds of sexual selec on.
Intersexual selec on: ma ng success determined by BETWEEN SEX INTERACTION! Female choice of
males. Males evolve to make themselves more a rac ve, females evolve preferences. (Females choice
can be overt or cryp c)
Intrasexual selec on: ma ng success determined by within sex interac ons, male-male combat, sperm
compe on (larger ejaculates and or larger sperm when other males are in proximity) females just go
with winner
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What is cryp c female choice:
This is a form of mate choice in which females mate with more than one male. The female uses
physical or chemical mechanisms to control a males success of fer lizing their ovum- if its an
unwanted male (some females can make their womb acidic and kill the sperm inside).
Iden fy and explain two major hypotheses concerning why females might sexually selected traits in men,
despite the survival disadvantages of those traits.
Male ornaments: Fishers “runaway” hypothesis:
—Females will select a male with a trait based on preference, therefore males with that trait will in
turn do be er. Females who prefer this trait will give rise to more successful males— “sexy sons”.
Theres a gene c correla on, between ornamenta on + the preference + producing good o spring.
Self-ful lling prophecy
Zahavi’s “male handicap” hypothesis: extravagant male traits are costly to develop and maintain.
Choosing a mate with good genes requires an honest signal of gene c quality.
-only males in good condi on (those with good genes) will be able to fully develop and maintain an
ornament “elaborate display:
-symmetry is indica ve of good genes!
-bright color honestly signals immunocompetence and parasite/ disease resistance
-asymmetry is indica ve of developmental instability and possibly “bad genes” symmetry is chosen in
some species
Who formulated the theory of parental investment, and what are its principles?
According to Trivers the compe
termed parental investment.
on underlying sexual selec on is really about a resource that he
Parental investment: any investment by the parent in an individual o spring that increases the
o springs chance of surviving and reproduc ve success: At the cost of the parents ability to invest in
other o spring. — emphasizing tradeo
-The sex that invests more in o spring (typically but not always, the female) will be choosier about
mates- the sex that invests less will compete for sexual access to the high inves ng sex. This is because
typically the lower inves ng sex will experience greater variance in reproduc ve success
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Which sex typically has the lower variance in reproduc ve success: the lower-inves ng sex or the higherinves ng sex?
Lower inves ng sex has a high variance and the higher inves ng sex has lower variance. High variance
meaning some individuals in popula on reproduce a lot and some do not at all, low variance meaning
the range of number of o spring is small.
According to Trivers, which sex will typically be choosier about mates, and why?
Females, because they invest more in o spring which leads to them being choosier about mates
Batemans principle: females o en invest more energy into producing o spring than males and
therefore in most species females are a limi ng resource over which the other sex will compete.
What is the key nding reported by Laura Betzig in her analysis of reproduc ve skew in humans?
In her paper, what societal form is characterized by the most extreme reproduc ve skew, and why? What
gene c evidence complements the conclusions in her paper?
— extreme skew in full me ancient farmers (big di erence in the amount of o spring between
di erent men- high upperclass and low upper class)
higher class in full time farmers they didn’t move around so had more resources and
passed down then poorer — also men practicing polygony so a few men have many
women (some men excluded entirely)
minimal skew in hunter and gathers — men not have many differences in the amount of
offspring— very common among all men to have similar amounts of offspring
hunter and gathers moved around a lot so they all couldn't keep a lot of resources so
they all had similar wealth of resources
polygonous= intrasexual compition among men to reproduce
Describe the di erent ma ng systems, including monogamy, polygyny, polyandry, and promiscuity.
1. Monogamy: one male mates exclusively with one female
2. Polygamy: individuals mate with more than 1 partner
3. Polygyny: some males mate with more than 1 female
4. Polyandry: some females mate with more than one male
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5. Promiscuity: males mate with more than 1 female and visa versa
What is lekking?
- Males aggregate in par cular areas called leks, display for females and then females choose a mate
— o en dominant male or male in the center
-In Jacana birds, exhibit harem polyandry and sex role reversal. Males maintain small territories, males
perform parental care, females mate with mul ple males and then leave eggs with male
-The number of males a female mates determines her reproduc ve success because she doesn’t care
for eggs,
Characterize the rela ve prevalence of these di erent ma ng systems across human cultures.
Under what circumstances does polyandry tend to emerge?
Humans can be monogamous, polygons or promiscuous. Socie es can be classi ed by the norm/ what
is legally recognized (over 80 percent of humans are polygynous- like men have mul ple wives at some
point in their life
-Polyandry emerges when males become a limited resource for reproduc on. Very rare in humans —
this happens when low o spring survival requires male parental care
Sexual dimorphism: females larger than males by 60 percent in mass (unusual for birds), females
aggressively ght other females and also kill their chicks
What is the opera onal sex ra o (see textbook)? What are the consequences of polygyny for the
opera onal sex ra o, and how does this in turn a ect male behavior?
Opera onal sex ra o: the opera onal sex ra os in human groups will be male biased (that is M/F >1)males will compete with other Males and females will exercise mate choice. — low parental
investment (since this increase breeding cost to females) and high variance in male quality
(Fer lizable females over sexually ac ve males)
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-When this ra o is high, the reproduc ve bo leneck rests with males and females could compete with
other females for the available males. When the ra o is low, the situa on is reversed and males will
compete with other males for the sexual favors of fewer females.
- in Polygyny that a ects the opera onal sex ra o by males being more choosy so M/F < 1— high
parental investment — high varia on in female quality
Approximately what percent of mammalian species are monogamous?
Only 3 percent - most are polygynous
Why is sex an evolu onary puzzle?
The cost of males: if you’re a gene in a female, you can be in all o spring (not half) through asexual
reproduc on
Cost of recombina on: breaking up a winning design
Cost of ma ng: search costs, a rac ng a mate….
Explain the Red Queen Theory? Why is it called that?
(Sex as a defense against parasites)
-parasites are always evolving. There are many of them, both in terms of numbers and in terms of
variety. They have much shorter genera on mes than their hosts do (and thus can evolve within a host)
-parasites in a host are selected to exploit that par cular hosts biochemistry
Based on characters/themes from books by Lewis Caroll, Through the Looking Glass. The queen tells
Alice in her country everyone is always running but never gets anywhere. Metaphor for
coevolu onary races between a host and the parasite. Parasite will exert evolu onary pressure on
host to evolve a defense (ge ng ahead in the race).l Parasite evolves in response and cycle con nues,
so nobody is ever ahead in the race. Sex is a tool for hosts to use to get ahead in the race because
parasites are small and reproduce very fast and can evolve while within a host- selected to mess with
hosts biochemistry,. William Hamilton states that Sex will force parasites to re adapt to a new
environment every genera on.
De ne polymorphism.
Sex adds variability if and only if there is gene c polymorphism (2 or more alleys at a single locus) in
breeding popula ons.
-Theory only works if there is variability within popula on!
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Explain how Cur s Lively’s experiments with C. elegans (in Morran et al., 2011) support the Red Queen
hypothesis. Overall, which individuals exhibited the lowest mortality when exposed to co-evolved
parasi c bacteria a er mul ple genera ons: obligate selfers, wild type, or obligate outcrossers?
— We are going to have an independent variable based on exposure to parasite and control condi on
is not exposed to parasite (control group- nothing going to happen for 30 years)
Outcome Variable: Is the rate of sexual reproduction increasing in the population or not?
- if no exposure to parasite the red queen theory states everything should be the same
-we are going to subject a worm to the parasite and we are going to let the parasite coevolve (everyone is going to be able to run!) -= if thats the case then the individuals who are
having sex (reproducing) should do better
-third condition is we expose worm to parasite but for each iteration we go back to the
freezer and we expose it to the orginal version of the bacteria (dont allow bacteria to
evolve-- cant run, cant catch up!) - based on red queen theory the worm will reproduce
more sexually and the parasite wont be able to keep up so the worm is in the lead and stays
ahead
sexual reproduction linked to less mortality
-Obligate selfers that co-evolved with the coevolving parasite had a very high mortality
- Obligate outcrossers that coevolved with the coevolving parasite had very LOW mortality
all of the obligate selfers, wild type, or obligate outcrossers that were frozen (could not
reproduce sexually) all had very high mortality
What is anisogamy?
Di erent sized gametes - females have bigger gamete size
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-Males produce small gametes called sperm while females produce larger gametes called eggs
Males— Small gametes, large numbers and energe cally cheap
Female- Large gametes, small numbers, energe cally costly
— The consequences of anisogamy percolated through 100s of millions of years of evolu on and will
con nue to do so for the rest of the course
What is disrup ve selec on? See lecture for di erences from direc onal selec on and stabilizing
selec on.
3 selec on types:
-Disrup ve Selec on
-Stabilizing Selec on
-Direc onal Selec on
disruptive Selection: Produces a population that has two extreme v versions of a trait as the
dominant phenotype
Ex: If both short and tall organisms, but not medium height organisms were favored this
would be disruptive selection in action.
difference between directional and stabilizing:
-directional selection: A type of natural selection in which the phenotype (the observable
characteristics) of the species tends toward one extreme rather the mean phenotype or the
opposite extreme phenotyp
Ex: Beak size in a population of nches
stabilizing selection: When selective pressures select against the two extremes of a trait, the
population experiences stabilizing selection.
Ex: A plant that is too short might not be able to compete with other plants for sunlight
Life History Theory
From the perspec ve of life history theory, what is life?
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-life requires the acquisi on and alloca on of energy
—The ability to capture energy from the environment and convert it into o spring
-The body is a set of adapta ons built by the genes that do this process
Iden fy and describe the three domains of investment, according to life history theory.
-Energy is a limited resource, energy spent on one ac vity necessarily cannot also be spent on another
ac vity — gives idea of tradeo
-Growth/development
-Soma c maintenance—(Brain energy and defending body)
-Reproduc on
What kind of adapta ons does life history theory focus on?
—Bodies possess adapta ons that manage how to allocate me and energy to growth, maintenance
and reproduc on.
-These adapta ons a ect (a) how long you live and (b) how much of that me you can devote to
reproduc on. Traits that increase (a) usually reduce (b)
-Generally longer life span= less me devoted and vice versa
Iden fy and describe the three major tradeo s highlighted by life history theory.
1. Current vs future reproduc on!
2. Quan ty vs Quality of O spring
3. Ma ng e ort and paren ng e ort
Invest in growth, maintenance/immaturity or reproduc ve e ort. Why aging and dying occurs (why
don’t we live forever?) — extrinsic mortality is inevitable, if you invested resources to trying to
maintain the body forever, some of those resources would necessarily go to waste, so they are
allocated instead to reproduc on— as a result the body eventually decays
What is antagonis c pleiotropy?
Genes with bene cial e ects in youth will persist even if they have very nega ve e ects on health/
condi on at later ages
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An example of this would be: Calcium! It is good at younger ages but then calci ca on occurs (bad at
later ages
Which is stronger: selec on on traits expressed at a young age, or selec on on traits expressed at an
older age?
Selec on is stronger on traits that are expressed at younger ages because more of the popula on is
alive to be selected
How does life history theory encompass, or relate to, parental investment theory?
-Since parents have limited resources to invest, many o spring (lower resources per o spring), the
op mum is typically lower than the level that would ensure maximum o spring quality
Because of anisogamy (di erent in size in gametes- female gamete is bigger)- the op mum tradeo s
between ma ng e ort and paren ng e ort are di erent for males and females. Can also adjust
depending on current fer lity
How does a species that exhibits an r strategy (fast life history) di er from one that exhibits a k strategy
(slow life history)?
— Related to the amount of o spring and the size of the body and speed of lifespan and amount of
parental investment.
-The scale goes from R to K
-Oysters are an example of a very R strategy. They produce 500 million fer lized eggs a year and
provide no parental care. Great apes are an example of a very k strategy, they produce an infant every
5-6 years and extensive parental care
What kind of physiological mechanisms are understood to implement adap ve switching between
domains of resource alloca on, as posited by life history theory?
— Endocrine mechanisms- hormones regulate trade o s, system is well suited for this because it an
in uence many organs at once plus e ects can be quick or slow and steady with long term e ects
Sex hormones:
-Andrenarch- (6-11 years of age) the adrenal gland produces androgens (mild sex hormone
prepara on)
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-Gonadarche (12+ years of age)— the gondads produce androgens and estrogens
-can be thought of as developmental switches that transi ons from 1 stage of development to the
next.
-2 of the most obvious switches are testosterone (man) and estradiol (women)
Estradiol: Female- will drop around 50
Testosterone: Male— trails o but stays high
—Both sexes have some of both!
How is testosterone understood to be linked to life history changes in men?
-Partner status and parental status, greater testosterone= greater ma ng e ort + success
Summarize the evidence provided by Ge ler et al., 2011, in support of the role of testosterone in
regulate male ma ng and paren ng e ort.
-Single non-fathers with greater AM (in the morning) Testosterone at base line were more likely to
become newly partnered and to become newly partners new fathers
-Thus, testosterone predicts transi on into a ma ng rela onship and into fatherhood
Less testosterone— fathering behavior (caregiving)
More testosterone— pair bonding behavior (partnering)
Describe human life history characteris cs as compared to those of the other great apes, especially
chimpanzees. What human life history features stand out as par cularly dis nc ve?
-Humans have a lot longer life span (slower life history trait) than chimpanzees
- Humans Shorter inter birth intervals than chimps (3.7 years vs 5.5 years)
- Humans have later age at rst birth compared to chimps and bonobos (slower life history trait)
- Humans have larger female body weight compared to bonobo and chimps (slower life history trait)
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- Humans have a longer gesta on length (how long baby stays in womb) compared to bonobos and
chimps (slower life history trait)
- Humans have a earlier age at weaning (giving a en on to next o spring than chimpanzees (we
don’t expect that) same thing with numbers of years in between births (we are faster than
chimpanzees)- faster life history with these two traits
Anomalies- Early weaning and short inter birth interval stand out — point out male investment (pair
bonding) and coopera ve breeding/ alloparental support
Describe age- and sex-based pa erns of food produc on for both chimpanzees and human foragers.
-Humans have a long period of juvenile dependency
-Humans are nutri onal dependent on others un l adulthood
-Women survive beyond fer lity
-Humans have shorter inter birth intervals than chimpanzees (3.7 yrs vs 5.5+ yrs) greater reproduc ve
output.
What is a key conclusion of life history analysis of human beings, with respect to produc on and
consump on of calories?
— -Long period juvenile dependency
-Nutri onally dependent on others un l adulthood, and again a er 60.
Stacked dependent, entailing massive energy demands on the mother (in ancestral condi ons) —
therefore other people help mother feed children (paternal investment) in hun ng food
Short inter birth intervals and the amount you have to hunt to feed the kids was a big strain on
mothers
short interbirth intervals combined with stacked, highly altricial dependents lead to massive calorie
de cits that cannot be lled by human (foraging) mothers in isola on. Coopera ve breeding was
therefore essen al in human evolu on, likely exer ng strong pressure favoring paternal investment.
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What is the “grandmother hypothesis” (see textbook)?
-related to the idea that if there is calorie de cit where are the calories coming? Coming from
grandmothers — helping to collect resources and give those resources to their daughters who are
facing a lot of burdens
What would a slow life history in a human look like compared to a fast life history? Be familiar with the
model proposed by Ellis et al. (2012).
Fast life history traits: (R is fast)
Early age of reproduc on, early puberty, a lot of sexual partners, a lot of o spring, ac ng aggressively,
not coopera ng, being impulsive, not inves ng as much
Slow life history traits: (K is slow)
Late onset of puberty, few sexual partners, having children late in life, coopera ng a lot, inves ng a lot
in the children you do have, delaying gra ca on, avoiding impulsive behavior, not taking risks
What a ects fast or slow life history?
-Mortality risk, a achment , environmental harshness, es mated life expectancy
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According to the model of human life history put forward by Ellis et al. (2012), greater
(percep ons of) mortality risk and faster life history should be associated with which of the following:
less vs. more coopera ve tendencies; less vs. more risk-taking; early vs. later sexual debut; more vs.
fewer sexual partners; more vs. less parental investment?
—
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What is the “demographic transi on” (see textbook)? Why is the demographic transi on more di cult
to explain from the perspec ve of human behavioral ecology and life history theory, than from the
perspec ve of evolu onary psychology?
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chimps..
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Note: Overview of Human Evolu on will not be on Exam 1, but will be on the Final Exam