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8/9/2019 The Evolution of Human Behaviour
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The Evolution of
Human BehaviourChapter 14 Alcock (Animal Behavior)
Prof. Tom Wenseleers
Ethology &Ethology &BehaviouralBehavioural
EcologyEcology
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The sociobiology controversy
Tests of sociobiological theory
Adoption ate preferences
!oercive se"
Parental care
Plan of lecture
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#. The sociobiologycontroversy$
the clash bet%eenscience and ideology
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!harles &ar%in
Application of evolutionary theory to humanspecies goes bac' to &ar%in
1859: The Origin of Specie
Traits evolve according to la%s of nat. selection
18!1: The "ecent of #an
#()*$ The $%preion of $motion
Applied his theory to the evolution of human
behaviour and society+ e.g. in relation to thehuman psyche+ social behaviour and e"pected
differences in behaviour bet%een the se"es
Emphasi,es our animal descent
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#-/0#-1)$ modern evolutionary synthesis+ e.g.
development of modern population genetics+
proof that natural selection %as compatible %ithgradual evolution+ etc...
2ome big names$ 3onald 4isher+
5.B.2. Haldane+ 2e%all Wright+ etc...
#-/6s0)6s$ application of the modern
evolutionary synthesis to the evolution of animalbehaviour+ caused increased interest in the
application of evolutionary theory to human
behaviour
&illiam 'amilton$ development of a ma7or
e"tension of the modern evolutionary synthesis$inclusive fitness theory
oert Triver$ reciprocal altruism+ parent0
offspring conflict+ se"ual conflict
#a*nar+ Smith$ application of economic thin'ing
to animal behaviour$ evolutionary game theory
The modern evolutionary synthesis
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E.8. Wilson. #-)9.
Socioiolog*: the ne, *nthei
About the evolution of social behaviour
in the animal 'ingdom: last chapter
about evolution of human behaviour.
;ave a popular account of theories
developed by evolutionary biologists
such as W.&. Hamilton+ 3. Trivers and
5.. 2mith
Heavy criticism+ mainly stemming from
various misunderstandings aboutevolution+ or politically motivated
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(i) -,e h.man +on/t +o thing eca.e ,e ,ant to raieo.r incl.ive fitne0 rather ,e .t +o them eca.e it ipart of o.r c.lt.re (-c.lt.ral relativim2)3 Alo0 man* c.lt.recannot e%pre fraction o the* cannot poil* kno, theirincl.ive fitne32 (Am3 Anthropologit #arhall Sahlin)
We don?t need to be a%are of ultimate reasons for behaviorto engage in adaptive behavior.
@t?s enough that pro"imate mechanisms motivate us to dothings that increase our direct or inclusive fitness
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(ii) -ot all h.man ehavior i iologicall* a+aptive an+ ifvario. c.lt.ral practice appear .nlikel* to a+vance
in+ivi+.al fitne3 Socioiological thinking in/t a .ef.l ,a*
of .n+ertan+ing h.man ehavior3
This assumes that all traits of an organism must becurrently adaptive+ %hich is not the case. E.g. evolutionary
psychology ma'es the specific point that many traits may
only have been adaptive in our ancestral environment .Evolutionary biology provides an intellectual toolset to
address interesting uestions in human behavior by
generating and testing plausible evolutionary hypotheses.
!riticisms %e sometimes behave maladaptively
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!riticisms genetic determinism
(iii) -'.man ehavio.r i not entirel* geneticall*+etermine+0 man* ehavio.r are learne+ or
ac6.ire+ via c.lt.ral procee32
sociobiology never claimed that human behaviour
is entirely genetically determined
dual inheritance theory$ loo's e"plicitly at gene0
culture coevolution
the genetic heritability of many traits is also very
high
cultural traits are also often inherited from
parents: in that case an evolutionary approach
can be used irrespective of the fact that the trait
in uestion is culturally determined
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Behavioural genetics
Geneticheritability(own genes)
Sharedenvironment(e.g. parentalinfluence)
Non-sharedenvironment(i.e. uniqueinfluences)
2i,e as an adult )( ## ##
Ceuroticity 96 6 96
2ocial responsability 1* * 9
3eligiosity
*# 1/
3eligion #* 9# )
2ilventoinen et al. T,in e3*66: Bouchard D c;ue 73 e.roiol3*66:
&?8nofrio et al. 73 er3#---: endler et al.Am3 73 ch3#--): 3ushton roc3 o 3 Soc3*661
Fariance in traits can be split up$ FtotGFgFseFne
heritabilityGFgIFtotGcorrelation in behaviour bet%een J t%ins reared apart
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&ual inheritance theory
&a%'ins $ suggested that the spread of cultural variants could be analysed by anevolutionary logic
=ater formalisation$ gene0culture coevolution I dual inheritance theory
!ultural transmission can either be vertical or hori,ontal .4itness of a meme$ cultural fitness.
3elatively high mutation rate compared to genetic inheritance
Luca avalli-Sfor!a "arcus #eldman $obert %oyd &ete $icherson Susan %lac'more
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!ultural traits often
inherited from parents
!avalli02for,a et al. Science#-(*
3eligion often inherited from mother
igh cultural heritability
!ultural heritability G regression of culturally determinedtrait in offspring on trait in parents
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!ultural phylogenies$ linguistics
;ray D At'inson at.re*66
2imilarity in vocabulary acrosslanguages also allo%s the construction
of language phylogenies+ shedding
light on their historical relationship.
)nglish
tree
house
Germ
an
bau
mhau
s
*nglo
-Sa+on
treow
hus
Norw
egia
n
trehus
!e
ch
strom
domovn
i
Spanish
arbolc
asa
,talian
albero
casa
$om
ania
n
arbore
cas
a
Latin
arbor domus casa
#rench
arbre
maiso
n
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!ultural phylogenies$ literature
Barbroo' et al3 The phylogeny ofthe !anterbury Tales. at.re -1$ (-
$elationship amongvarious versions ofhistorical manuscripts+ such as The
Canter.r* Tale0 can be determined using
phylogenetic methods from biology
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!ultural phylogenies$ artefacts
Tem'in D Eldredge C.rrent Anthropolog* *66)
Evolutionary trees can also be constructed for
cultural artefacts such as te"tiles+ pottery+music instruments+ arro% points+ etc....+
shedding light on their historical relationship
and on innovation in design over time.
Baltic palter* cornet
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(iv) -$vol.tionar* approache to h.man ehavior are ae+ on apoliticall* reactionar* +octrine that .pport ocial in.tice32
This criticism %as based on fear that sociobiology %ould be
used as scientific cover for legitimising social ineuality+ e.g.
bet%een races or the se"es.2cience has certainly been used to 7ustify some odious practices
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The Caturalistic 4allacy
5ustifying certain ineualities based on
evolutionary theories is a mista'e because
one cannot assume that %hat is natural is
also good+ this is the naturalistic fallacy
;eorge Ed%ard oore
rincipia $thica
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2ocial in7ustice D eugenics
erbert Spencer $ ) years before the publication of The
Origin of Specie$ "evelopment '*pothei @ntroduces the concept of the S.rvival of the ittet0 founder of 2ocial
&ar%inism
Against interference from the state: proponent of laisse,0faire politics
Humanitarian impulses had to be repressed
But$ 8nly vaguely connected to &ar%inism+ some ideas rather based on=amarc'ism
#rancis Galton
4ounder of the eugenics movement
Thought that human race could be improved via artificial selection+ as in
applied animal D plant breeding 8ften based on pseudoscientific notions of racial supremacy
@nterference from the state encouraged
But$ &ar%in distanced himself clearly from eugenics
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ilitarism
E.g. in ;ermany &ar%inism has
been used to rationalise militarism
Hitler in #ein ampf $
-'e ,ho ,ant to live m.t fight an+
he ,ho +oe not ,ant to fight in thi,orl+ ,here eternal tr.ggle i the
la, of life ha no right to e%it32
Sociobiologyho%ever struggles
to e+plain the evolutionary basis
of warfare$ if anything+ everyoneshould be better off deserting+ and
pacifism should be the rule
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3acism
&ar%in$ paternalistic attitude
to%ards other cultures+ but
also emphasi,ed that there
are more commonalities thandifferences among races+ and
also strongly opposed slavery
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2e"ism
N OriginO $ supports certainpatriarchal norms
2ociobiology also emphasi,es
certain e"pected differences in
behaviour bet%een the se"es
But by no means implies that one
se" %ould be in some %ay
superior to the other+ or that they
shouldn?t have eual rights
2teven Pin'er$ men certainly
aren?t depicted any better in
evolutionary psychology than
%oman
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2ociobiology today
Because of the perceived negative connotations of
the term sociobiology researchers started to use
other labels+ e.g. evolutionary psychology+ human
behavioural ecology+ dual inheritance theory+behavioural and e"perimental economics+
evolutionary game theory+ etcQ
@n all of these fields the evolutionary study of humanbehaviour has since proved to be a big success
2ociobiology also e"tensively tries to e"plain social
behaviour+ as opposed to selfish I egoistic behaviour
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Alternative to evolutionary approach$
!ultural relativism ain alternative to an evolutionary approach is
that human behavior is a result of culture+ %hose
development may arise from historical accidentor by arbitrary processes.
Predictions of sociobiology can be compared
%ith those of arbitrary culture theory.E.g. adoption
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*. Test case$ adoption
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Test$ adoption
arshall 2ahlins $ criticised sociobiology.Pointed out that adoption is very freuent on many
islands in the central Pacific . Rp to 6
of all children are adopted. He regarded adoption as
an arbitrary cultural tradition and sa% sociobiologyas irrelevant for understanding human behaviour.
Anthropologist 5oan 2il' $ tested %hether
adopted children %ere related to the adopters in ##cultures in 8ceania. @f they are related+ then
adoption can raise the inclusive fitness of the
adopters.
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Adoption and relatedness
Adopted children are usually nephe%s or nieces
Adoption of relatives confers an inclusive fitness advantage
5. 2il' Adoption and 'inship in 8ceania.American Anthropologit(*$ )--0(*6.
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Evolution of human behavior$
Arbitrary culture theory
But some adopters also adopt children %hose degree
of relatedness is very small or non0e"istent.
!an this be e"plainedS Adopting non0relatives appears to be beneficial in
agricultural societies %here e"tra hands increase the
farm?s productivity and enhance the survival of the
adopter?s genetic offspring.
!onsistent %ith this hypothesis small families in
8ceania are significantly more li'ely to adopt than
larger ones.
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Evolution of human behavior$
Arbitrary culture theory An alternative e"planation is that some decisions may be
maladaptive by0products of other%ise adaptive pro"imate
mechanisms. Adopting non0relatives+ thus+ may be
maladaptive+ but caring for children is usually adaptive.
Pro"imate desires strongly affect
our behavior so that in satisfying those desires %e
sometimes do not ma"imi,e our inclusive fitness.
Also supported by observations of non0humans engagingin similar behaviors+ e.g. penguins that have lost a chic'
may adopt an orphan .
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#1.
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Adaptive mate preferences
Human cultural rules concerning se"ual
behavior and mate selection are very
diverse.
&espite large cultural differences certain
basic aspects of human reproduction are
consistent across societies and parallel
those found in other mammals.
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Adaptive mate preferences
4emale humans invest very heavily in individual
offspring and their life time reproductive success
is limited by ho% %ell they can care for offspring
rather than ho% many they can give birth to.
ales+ also invest heavily in their offspring+ but
in contrast to %omen+ have the potential to
produce many offspring .
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Adaptive mate preferences of men
;iven that females often reuire
considerable investment by males+ it
%ould be e"pected that males should be
'eenly interested in a female?s potentialfertility.
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Adaptive mate preferences of men
Women differ in their li'elihood of conception.
Healthy andIor younger %omen are more li'ely to
conceive than older andIor sic' %omen. 2imilarly+
over%eight or under%eight %omen are less li'elyto become pregnant than %omen of average
%eight.
;iven that females differ in fertility+ evolutionary
biologists %ould e"pect that males have beenselected to evaluate female fertility.
@s there a relationship bet%een %hat males
consider Kgood loo'sL and fertilityS
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Adaptive mate preferences of men
A cultural alternative is that males and
females have been culturally indoctrinated
to perceive KbeautyL in relation to a nearly
impossible standard designed to maintainfemale insecurity.
2o are standards of beauty arbitraryS
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Adaptive mate preferences of men
ales in %estern society generally prefer
females %ho possess$ full lips+ thin noses+
large breasts+ a %aist that is narro%er than
the hips+ and an intermediate %eight.
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Adaptive mate preferences of men
The listed traits are associated %ithdevelopmental homeostasis+ a strong immune
system+ good health+ high estrogen levels and
youth.
!irculating levels of estrogen+ for e"ample+ are
related to body shape in Polish %omen.
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Adaptive mate preferences of men
any physical features in %omen that
men find attractive are lin'ed to fertility.
Women can only become pregnant at the
time of ovulation. Thus+ %e %ould e"pect
males to be attuned to cues that signal
ovulation.
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Adaptive mate preferences of men
ales do e"hibit these traits.
en find the scent of a T0shirt %orn by an ovulating%omen se"ier than that %orn by a non0ovulating
%oman.
2imilarly+ men rate as more attractive+ facial photosof %omen ta'en during their period of ovulation thanpictures ta'en %hen the same %oman %as notovulating.
2ingh D Bronstad 4emale body odour is a potential cue to ovulation. roc3o*3 Soc3 ;on+3 B*/($ )-)0(6#.3oberts et al. 4emale facial attractiveness increases during the fertilephase of the menstrual cycle. Biolog* ;etter*)#$ *)60*)*.
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3oberts et al. 4emale facial attractiveness increases during the fertile phase of the menstrual cycle.
Biolo ;etter*)#$ *)60*)*.
follicular phase luteal phase d d
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follicular phase
luteal phase
3oberts et al. 4emale facial attractiveness increases during the fertile phase of the menstrual cycle.
Biolo ;etter*)#$ *)60*)*.
udged
most attractive
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Adaptive mate preferences of men
!onclusion$ cues males use in assessing
attractiveness of partners appear to have
a significant selective advantage
associated %ith them+ %hich is notconsistent %ith the cultural e"planation.
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Adaptive mate preferences of %omen
Women also e"hibit adaptive mate
preferences.
Human females appear to rate capacity of
males to supply good genes and to
provide resources highly %hen evaluating
potential mates.
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Cumerous studies have reported that females e"press a
preference for men %ith KmasculineL features$ a
prominent chin and strong chee'bones+ athletic and
muscular upper body and facial symmetry.
These features have been lin'ed to high testosterone
levels+ good health and developmental homeostasis.
Evolutionary basis for these preferences may be that
males can pass their genes for attractiveness to their
children or that these traits are correlated %ith ability to
secure resources.
Adaptive mate preferences of %omen
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2tudies have documented females have
preferences for male physical appearance
but most researchers have concluded that
loo's are much less important for singlemen than single %omen.
@nstead+ the difficult tas' of rearing
offspring to maturity has selected femalesto focus on securing a mate %illing and
able to assist %ith child rearing.
Adaptive mate preferences of %omen
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!onsistent %ith this idea many studieshave sho%n that %omen prefer males %hocan supply resources and that this
preference enhances fitness.
E.g. %omen %ith %ealthier husbands in
societies %here there is no birth controlhave higher lifetime fitness than %omen%ith poorer husbands.
Adaptive mate preferences of %omen
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Women %hose husbands are good hunters
produce more surviving offspring among the Ache
of Paraguay.
2tudies of %omen in Africa and @ran sho% that a
%oman?s reproductive success is related to her
husband?s %ealth.
Even in modern %estern societies income is
correlated %ith children?s health and chronic
illness in childhood can reduce earning po%er in
adulthood+ perpetuating the cycle of poverty.
Adaptive mate preferences of %omen
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;iven the importance of resources to %omen?s
prospects of enhanced reproductive success it
%ould ma'e evolutionary sense for females to
favour %ealth+ status and po%er over good loo'sin a partner.
&ata from personal ads provide relevant evidence of the features
most valued in a mate$ males across culturesconsistently see' younger partners and females see' older
partners.
Adaptive mate preferences of %omen
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Adaptive mate preferences
#1.)
ales generally see' younger partners and femalessee' older partners.
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2chmitt et al. 73 er3 Soc3 *ch3*66
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!onditional mate preferences
What people %ant in an ideal mate and
%hat they can obtain are not al%ays the
same.
The supply of the most desirable mates is
limited and people employ conditional
strategies in mate selection that reflecttheir o%n attractiveness as mates.
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!onditional mate preferences
4or e"ample+ females %ho rate their o%n attractiveness
highly sho% a stronger preference for both relatively
masculine and symmetrical faces
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!onditional mate preferences
2imilarly+ both males and females %ho consider
themselves high ran'ing mate prospects e"press a
preference for similarly highly ran'ed mates.
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2e"ual conflict
Because male and female fitness interests
do not necessarily coincide se"ual conflict
is li'ely.
8ne significant area of conflict is male?s
on average greater interest in multiple
se"ual partners.
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2e"ual conflict
en consistently e"press a greater interest in having
multiple se"ual partners over a given time period than
%omen.
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2e"ual conflict
en and %omen also differ in ho% li'ely they %ould be to
have se" %ith a partner after 'no%ing the individual for
different lengths of time.
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2e"ual conflict
en are less selective in the choice of a partner
!lar' D Hatfield 73 *ch3 '.m3 Se%3#-(-
ales 4emales
KWould you go out %ith me tonightSL
KWould you come to my appartmentSL
KWould you go to bed %ith me tonightSL
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en are less selective in the choice of a partner
!lar' D Hatfield 73 *ch3 '.m3 Se%3#-(-
ales 4emales
KWould you go out %ith me tonightSL 96 9/KWould you come to my appartmentSL /- /
KWould you go to bed %ith me tonightSL )9 6
2e"ual conflict
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en are less selective in the choice of a partner+ particularly
in the conte"t of short0term relationships
&avid Buss en team van 96 %etenschappers bestudeerden#6+666 mensen
in ) culturen
op / continenten
%esluit se'se verschillen in selectiviteit partner'eu!e !in universeel
2e"ual conflict
2h t t l ti hi D
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2hort0term relationships D
e"tra0pair paternity 2hort0term relationships$
in men+ %e might e"pect
these$ small cost+ potentially
large fitness advantage
But also %oman engage inshort0term relationships$ ca.
*09 of all children are
e"tra0marital
%hyS;enetic father %ith good
genes a good parent
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2e"ual conflict
Polygynous men can potentially achieve substantially
higher reproductive success than monogamous men and
polygyny has been %idespread in human history.
Women+ ho%ever+ are li'ely to do %orse in a polygynous
system.
4or e"ample+ in #-thcentury Rtah monogamous ormon
%omen married to relatively poor men had more
surviving children on average than %omen married
to rich polygynous men . The polygynous men+ of course+ did much better than
the monogamous men.
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2e"ual conflict
Potential benefits of polygyny to males
increase potential for conflict bet%een
mates.
Ho%ever+ females may also opt for e"tra0
pair matings if these offer better genes+
more resources or the possibility oftrading0up to a better partner.
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2e"ual conflict
2e"ual 7ealousy is li'ely an evolutionary
conseuence of the conflict bet%een the se"es.
The conditions that cause the most intense
e"pression of 7ealousy appear to differ bet%eenthe se"es.
ales respond most to a potential loss of
paternity and se"ual infidelity %hereas females
e"press greater concern %hen their matesdevelop deep emotional relationships %ith other
%omen+ %hich threaten the long0term
partnership.
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1. !ontroversy$ coercive se"
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!oercive se"
Thornhill D Palmer$ evolutionary biologists %ho
%rote a boo' on the natural history of rape
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!oercive se"
Ues+ raped %oman are most often in their early *6s+ %hen
they are ma"imally fertile. urder victims+ by contrast are
usually %ell into their 6s.
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!oercive se"
re6.enc* of tar cl.ter < chromoome haplot*pe3
Sha+e+ area=e%tent of >enghi han? empire at the time
of hi +eath.
!a. ( of all men in Asia carry a U chromosome haplotype that originates from male0
line descendants of ;enghis han .
Probably lin'ed to the slaughter+ pillage and rape e"ercised
during the many conuests of ;enghis han and his male0
line descendants .
#e+ian@oining net,ork of
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!oercive se"
!oercive se" also occurs in the animal 'ingdom+
e.g. in the @ron cross blister beetle.
=eft$ normal courtship pattern
3ight$ coercive se"
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9. Test case$ parental care
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Adaptive parental care
a'ing decisions that increase the
li'elihood that genetic offspring %ill
reproduce successfully and directing
resources so as to ma"imi,e the numberof grandchildren produced by offspring are
strategies li'ely to be favored by selection.
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Adaptive parental care
Humans appear to apply such strategies.
@t is %ell established that parents of genetically related and
stepchildren discriminate in resource allocation.
4or e"ample+ the odds that a man %ill give a child money for college
is much higher if he is the genetic father rather than the stepfather.
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Adaptive parental care
2imilarly+ stepmothers are less li'ely tocare for stepchildren than their o%noffspring.
Households in %hich a %oman cares forstepchildren+ foster children or adopted
children spend less on food thanhouseholds in %hich the mother cares forgenetic offspring.
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Adaptive parental care
&aly+ D Wilson+ . *66#. An assessment of some proposed e"ceptions to the
phenomenon of nepotistic discrimination against stepchildren.Annale oologici ennici
($ *()0*-/.
/ype of father
Genetic father Stepfather
V murders per million I yr *./ **
#+//9+666 #6+666
2tepchildren are also more li'ely to suffer abuse thangenetic children.
@n one !anadian study the relative ris' of abuse %asmuch higher for stepchildren than for genetic children.
Adaptive parental care$ assisting
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Adaptive parental care$ assisting
children?s reproduction
Parents not only discriminate bet%een
genetically related children and step
children+ but also discriminate among
genetically related children.
@n many societies parent commit
resources to enable their offspring tomarry.
Adaptive parental care$ assisting
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Adaptive parental care$ assisting
children?s reproduction
@n some societies the grooms family must contributeresources to the bride?s family+ %hereas in
others the bride?s family contributes a do%ry.
@f these payments are purely cultural %e %ould e"pect the t%o
forms to be eually common. Ho%ever+ they are not. 2e"ual selection theory suggests that because males usually
compete for females that bride%ealth payments should be
more common than do%ries.
@n // of societies studied bride%ealth payments occur+ butdo%ries in only . Bride%ealth payments are especially
common in cultures %here men can have more than one %ife.
@n these societies marriageable females are in demand and
so demand a price.
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asai fatherand his soon0to0be
0married daughter.
The father %ill have
received a
bride%ealth
payment beforegiving permission
for the marriage.
Adaptive parental care$ assisting
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Adaptive parental care$ assisting
children?s reproduction
Even in supposedly monogamous %esternsocieties rich men may have greateropportunities for reproductive success.
Parents in modern societies appear to retain anancestrally selected bias that favors investingmore in the offspring %ith the highestreproductive potential.
This sho%s in inheritance decisions. Wealthy!anadians bias their legacies to%ards sons.
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marriageable females in demand and so demand a price
sons have much greater
reproductive potential
Adaptive advantage of menopause
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01th-02th century
#inland anada
Age of having #st child *9.1 **.(
Age of having last child -. (.)
Cumber of children /.( -.#
Cumber of children that
survive to #9 years
.( 9.#
Cumber of grandchildren ##. (.*
=ife e"pectancy for %omenaged 96
/).9 )1.6
Adaptive advantage of menopause
=ahdenper et al. *661. at.re
Why stay alive past menopause given that %omen are no longer fertile thenS
Theory$ help rear grandchildren .
Adaptive advantage of menopause
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0
10
20
30
40
50
40 50 60 70 80 90 100
Total
number
ofgran
dchildren
=ife e"pectancy
!anada+ n G */*
4inland+ n G -
03 years of post-menopausal life results in
ca. 4 e+tra grandchildren
=ahdenper et al. *661. at.re
Adaptive advantage of menopause
Economic game theory
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co o c ga e t eo y
0conomic game theory$ aimed at determining %hat people
should do in conflict situations if they behaved rationally
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The future
E.8. Wilson proposed in #-)9 in his boo'
2ociobiology$ The Ce% 2ynthesis that
evolutionary theory %ould transform the
social sciences Was he rightSS
8nly the future %ill tell