Outline • Evolu-on Evolu-on and Development PSC 113 Jeff Schank – Change – Species – Phylogeny • Evolu-on by Natural Selec-on
– Influences on Darwin: Lyell, The Voyage, Malthus, Ar-ficial Selec-on
– Three Principles of Natural Selec-on: Varia-on, Heritability, Fitness
•
The Modern Synthesis
– Blending Inheritance – Mendelian Gene-cs – The Synthe-c View •
Units of Selec-on
– The Selfish Gene – Kin Selec-on and Inclusive Fitness
Outline con-nued • Adapta-ons
– Adapta-onist View: Ecological Niche (3 views)
• Ecological Niches are fixed targets of Natural Selec-on
• Red Queen Hypothesis (Leigh Van Valen) • Construc-vism (Richard Lewon-n) – Problems with Adapta-onism • Not all Characters and Behaviors are Adap-ve • Exapta-ons
• Constraints on Adapta-ons
– Unwelten, Niches, and Adapta-on
– Condi-ons for the Evolu-on of Adapta-ons
• Con-nuity • Quasi Independence Change • Evolu-on means change but change of what
kind?
• Change in gene frequencies in a popula-on?
• This defini-on is adequate if genes are programs or blueprints • Change in phenotypic characters and
behaviors over genera-ons
Evolu-onary Psychology 1 Species • Fixity of Species
– Species at the -me of the Origin, were viewed as fixed forms or kinds of things • Darwin began by arguing that species are not fixed but can
change • The modern view is that species consist of individuals reproduc-vely isolated (or nearly so) from other species
• Reproduc-ve isola-on does not imply that members of different species cannot inter breed, but only that there is a strong tendency not to (e.g., wolfs, coyotes, domes-c dogs). • Species are therefore not kinds of things but collec%ons of
individuals that persist over many genera-ons
Phylogeny • The great chain of being and the fixity of
species: Species as fixed kinds have a strict
linear order with the “lowest” forms of life at
the top and the “highest” forms at the top
• Darwin’s idea of evolu-on by descent was a
radical departure.
– In this sense, they are individuals that exhibit varia-on among their parts (the individuals that make them up) Great Chain of Being Evolu-on by Natural Selec-on: Key Influences on Darwin • Sir Charles Lyell’s Principles of geology – View at the -me: Geological was catastrophic, which was
mo-vated by the Biblical flood – It was cri-cal to see that natural process could change gradually but significantly – If changes occurred gradually, this would take a long -me • The Voyage – The idea that species can be related by descent – There is varia-on within species
• Thomas Robert Malthus
– Popula-ons grow exponen-ally but resources are limited
– Thus, not all individuals can survive – Which individuals are likely to survive to reproduce?
2 Evolu-on by Natural Selec-on: Key Influences on Darwin • Ar-ficial Selec-on
– Dog breeds
– Dogs and wolves
– Origins of dogs
– Are dogs a different species?
Three Principles of Natural Selec-on • Varia-on
– There must be some varia-on among phenotypic characters and behaviors • Heritability – Characters and behaviors must be to some degree inherited by offspring • Fitness
– Characters and behaviors must be beneficial in the struggle for existence in compe--on with others or in the struggle against the environment • Evolu-on by Natural Selec-on occurs when there is
heritable varia-on in phenotypic fitness The Modern Synthesis • Blending Inheritance
– Darwin proposed a theory of inheritance called
pangensis
– Each part of the body throws off some par-cles, which are collected in the reproduc-ve organs – Sexual reproduc-on blends these par-cles
together in the offspring. – Why is blending inheritance incompa-ble with
evolu-on by natural selec-on? Mendelian Gene-cs • Mendelian Gene-cs
– Mendel, a monk published his
paper on gene-cs in 1866. – He showed that there are hereditary factor affec-ng the phenotypic characters. – He discovered 7 pea characteris-cs: 3 Characters and their Varie-es F1 Genera-on 4 Mendel’s Conclusions • Inheritance follows definite simple rules.
– No blending of characters
– No modifica-on of characters through genera-ons.
– Mendel’s first law: segrega-on occurs between
factors – Mendel’s second law: Between pairs of factors
assortment is independent • Mendel did send a copy of his paper to Darwin,
though there is no evidence that he read it
• Do you think it would have affected Darwin’s
view of inheritance?
Units of Selec-on: The Selfish Gene • On this view, individual genes are the units of
selec-on
• They are the en--es transmiied during
reproduc-on
• They cause phenotypes, so even though
selec-on acts on phenotypes, selec-on can be
causally traced back to the genes
• Any problems with this view from what we
have talked about previously?
The Synthe-c View • From 1866 to 1900, Mendel’s paper went essen-ally unno-ced. • There were several reasons for this: – Mendel was not connected to the biological community of the -me. – It was thought that Mendel’s results were special to peas
• Hugo de Vries, Carl Correns, and Erik von Tshcermak “rediscovered” Mendel’s laws in their own experiments
• But, Mendelism was associated with sports (large muta-onal changes in phenotypes) • Ronald A. Fisher, Sewall Wright, and J. B. S. Haldane demonstrated mathema-cally that Mendelism was compa-ble with gradual evolu-onary change Kin Selec-on and Inclusive Fitness • How does social behavior evolve?
• Clearly some social behavior comes at costs to
individual fitness of individuals
– Eusocial insects are the paradigm • J. B. S. Haldane stated the essence of kin
selec-on with his statement (paraphrased):
– I would gladly give up my life for two sibs, or 8 first cousins, etc. -­‐-­‐-­‐-­‐-­‐J. B. S. Haldane • W. D. Hamilton captured the essence of kin
selec-on in a simple equa-on that describes the
concept of inclusive fitness
5 Hamilton’s Equa-on According to inclusive fitness theory, the fitness of a behavior is determined by the direct affect of the behavior on the fitness of the altruist, as well as the sum of the indirect fitness effects for all kin that are affected by the behavior (adjusted by the degree of rela-onship of the kin). Hamilton’s Equa-on: Analysis • Let’s set W = 0:
n
0 = Wd + ∑ rWi
i=1
• If altruism is favored then
n
0 < Wd + ∑ rWi
i=1
• We know that the direct effect of altruis-c
behavior, Wd, on the altruist is nega-ve
• So
n
n
i=1
i=1
0 < W
d + ∑
rW
i è Wd < ∑ rWi
• Thus, as long as the costs to altruist < benefits to
kin, the behavior will be favored by kin selec-on
Example Problems • if an altruist were to sacrifice its life, its fitness
would be Wd = –1
• If the altruist saves two sibs (n = 2) and their
relatedness is r = 0.5, then the indirect effect
of the behavior would be W = −1+ ∑ 0.5(1) = 0
• And the Altruist just
breaks even, but if we add a first cousin (r =
W = −1+ 0.5(2) + 0.125(1) = 0.125
0.125, we get
and an advantage for the altruist
n=2
i=1
• Altruism is most favored under condi-ons
when r > 0.5, which can result in costs of
inbreeding
• It is now known that there are many species
of eusocial insects with mul-ple unrelated
queens and workers kin selec-on is hard
pressed to explain these species
• Kin selec-on is typically interpreted from a
selfish gene perspec-ve
6 Another Interpreta+on Adapta-ons • Strong Adapta-onist view
• Inclusive fitness depends on the coefficient of relatedness, r • But, perhaps there is a more general mechanism that explains r? • Proximity: Individual that are in close proximity are more likely to
– Be related and/or – Exhibit similar behaviors
Adapta-ons • Weak adapta-onist view – Not all characters and behaviors are adapta-ons, some may have func-ons that have not been selected for – Adapta-ons are produced gradually by natural selec-on
– Organisms do not adapt to “problems” (for example finding food, avoiding predators, moving) in ecological
niches
– There no fixed “problems” because niches change in two
important ways • First, first other organisms, which are part of an organism’s niche are changing and hence changing the niche • Second, organisms ac-vely change their environment – Almost all if not all behaviors and characters of an organism are adapta-ons – Adapta-ons are produced gradually by natural selec-on
– Organisms adapt to “problems”
in their ecological niche – Typically, assume genes are the units of selec-on
Example of Strong Adapta-onist View • Sociobiology (Robert Trivers): Takes a strong adapta-onist view and parent offspring rela-ons are an example – Parents take care of young because they have a gene-c investment in them – They further invest resources into their young un-l the costs in
fitness to the parents outweighs the benefits the receive from their gene-c investment in their offspring • E.g., for unrelated sexually reproducing parents, the expected gene-c investment is 50%
– Thus, at some point there must be a conflict between parent and offspring – Offspring want to get all the resources they can parents want to
limited it to match their gene-c investment 7 Problems • First, the research does not necessarily support parent-­‐
offspring conflict, at least in all cases – Consider the example of 15 and 20 day-­‐old rat pups
• Second, Triver’s logic ignores the individual as the unit of selec-on
• An individual during development will be both
offspring and parent • They must be capable of expressing behavioral rules
for both stages of development • Natural selec-on should act act to op-mize the interests of both stages, which makes no predic-ons
about parent-­‐offspring conflict Ecological Niche: The Red Queen Hypothesis Ecological Niche: Fixed Targets • Ecological Niches are fixed targets of Natural Selec-on
– Defini2on: An ecological niche of an organism are all those
features of an environment that affect the organism’s fitness
– These features include the resources it can access, any predators, other organisms it is compe-ng with Not every aspect of the environment is part of an organism’s niche – Anything the organism does not interact with or that does not affect an organism’s fitness is not part of its niche, For example • For many birds, the upper parts of trees are part of their niche.
• While for many ground dwelling animals (e.g., many species of snakes
or mice), the shade of trees are part of their niche.
– The classical view is that there are niches in the world towards
which organisms are gradually adap-ng – Somewhat analogous to gradually filing a key to fit a lock Ecological Niche: The Red Queen Hypothesis • Characters and behaviors chase every changing niches
• Leigh Van Valen, recognized that niches are not sta-c “problems” of the environment • According to the defini-on of ecological niche given
above, niches must change! • Part of an organism’s niche are other organisms that are also evolving • Thus, niches are dynamic and not sta-c • The Red Queen Hypothesis asserts that organisms are in a perpetual state of adapta-on, chasing ever changing niches 8 Ecological Niches: Construc-vism • Richard Lewon-n has argued that niches are even more complicated • Organisms ac-vely: Problems with Adapta-onism • Not all Characters and Behaviors are Adap-ve, e.g., Scull sutures – Assemble: Organisms par-ally assemble their environments, •  e.g. many birds build nests, social insects build nests, spiders weaving webs. – Alter: In interac-ng with their environments they alter them.
• This is not necessarily the same as assembling • For example, masses of locusts devouring vegeta-ve maier in their path or elephants pulling down trees to feed on the leafy branches
– Transduce: The take in energy and perceive s-muli and produce physical products and behavioral interac-ons • Consider a female mammal nursing her young • She takes in energy in the form of food and transforms it into milk4.
– Modulate: They regulate their environments
• Even Army ants can control the temperature and climate of their nests.
Exapta-on • Behaviors or characteris-cs that have evolved
by natural selec-on for one func-on.
• Ritualized preening in birds may have been an
exapta-on for ma-ng rituals
• The evolu-on for the human thumb, not
selected for wri-ng
• Skull sutures in humans and other mammals are not adapta-ons for birth because they are present in rep-les and birds Constraints on Adapta-ons • Gene2c constraints: Not all characteris-cs and behavior are influenced by gene-cs
– Thus, characters and behaviors are not indefinitely malleable by natural selec-on
• Allometry: means different growth rates of body parts during development – Animals aren't simply linearly scaled up versions of themselves during development – Look at a baby, and their heads and eyes seem large rela-ve to the rest of their body
– As a baby develops there is a shit in propor-ons over -me, with the body growing faster than the head so that by adulthood they have
adult propor-ons
– These morphological changes are not necessarily adapta-ons, but rather differences due to rates of growth
9 Example Another Example Condi-ons for the Evolu-on of Adapta-ons Evolu-onary Psychology • If the construc-vist view of adapta-ons is correct, then successful
adapta-ons can occur only if there is • Con2nuity: “...very small changes in a character result in very small
changes in the ecological rela-ons of the organism and therefore very small changes in reproduc-ve fitness. So a very slight change in the shape of a fin or mammalian appendage to make it finlike cannot cause a drama-c change in the sexual recogni-on paiern, or make the organism airac-ve to a completely new set of predators.” • Quasi Independence: “there exist a large variety of developmental
paths by which a given character may change, and although some of these may give rise to countervailing changes in other organs and in other aspects of the ecological rela-ons of the organism, a non-­‐negligible propor-on of these paths will not result in countervailing effects of sufficient magnitude to overcome the increase in fitness from the adapta-on.” • Behavioral and Psychological Phenomena are
traits
• Behaviors and psychological phenomena have
effects on the organism’s environment and thus
have fitness
• There are constraints on evolu-on of adapta-ons
• Modularity: Different behaviors and
Psychological phenomena can evolve rela-vely
independently of each other
– Different genes affect different behaviors and
psychological phenomena 10 Iden-fying Psychological Phenomena as Traits • Evolu-on by natural selec-on and cultural evolu-on
occur on different -me scales • In general, it takes much longer for a trait to evolve in
a popula-on than traits to change as cultures evolve – For example, food preferences
• However, if certain preferences develop, even when
they do not fit current cultural preferences or knowledge, then evolu-onary psychologists suggest that they may have evolved by natural selec-on • Our “sweet tooth” is viewed as one example Evidence for Olfactory Preferences 1)
2)
3)
4)
5)
Men with more symmetrical faces are perceived to be healthier (Rhodes et al. 2001) More symmetrical men sexualize other women more and they invest less -me and emo-onal support in their primary partner (Gangestad & Thornhill 1997a); (More symmetrical men are more likely to have extra-­‐pair sex
partners and are more likely to be chosen as extra-­‐pair sex partners (Gangestad & Thornhill 1997b); Women are more likely to have extra-­‐pair sex mid-­‐cycle, a paiern
not observed for sex with a primary partner (Bellis & Baker 1990); and Women report greater feelings of sexual airac-on to and fantasy about men other than a current primary partner when fer-le, a paiern not observed for feelings about in-­‐pair partners (Gangestad et al. 2001). A More Detailed Example • Gangestad and Thornhill (1998; Thornhill &
Gangestad 1999) suggest that
• The shit in female olfactory preferences toward
the scent of symmetrical men when fer-le
• May be an adapta-on for seeking gene-c
benefits for offspring in the context of extra-­‐pair
sex
• That is, women may pay a cost (e.g., loss of an in-­‐
pair mate’s investment in offspring) and can only
reap the gene-c benefit when fer-le
Problems with Evolu-onary Psychology • If evolu-onary psychology as an adapta-onist
program is going to yield a number of important
results, then a number of behavioral and
cogni-ve processes must be modular, i.e. have
rela-vely liile influence on each other
– There is liile evidence for this assump-on
– In psychology, the opposite assump-on is usually made • Where are all the genes?
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