Human Evolution and Evolutionary Psychology

Human Evolution and Evolutionary Psychology
Order Description
The title of the essay is “Compare and contrast the mate choice strategies of males and females and explain why the various gender differences and similarities exist. To what extent are these differences relevant today ?” This question is drawn from a lecture called ” Sexual Selection” given as part of a module called ” Human Evolution and Evolutionary Psychology ” in the final year of a BSc in Psychology.
Please note there are two parts to the question and they both need to be addressed: compare and contrast from an evolutionary perspective as well as the second one being comparison with nowadays.
I’ll provide lecture slides and here is a list of references recommended by the lecturer:
Dunbar. R., Lycett. J. & Barrett. L., (2007) Evolutionary Psychology: A Beginner’s Guide (Beginner’s Guides) OneWorld Publications Chapter 5 sexual selection ;
Nettle. D (2009) Evolution and Genetics for Psychology, OUP Chapter 6 – Sexual Selection;
Swarmi, V. (2011) Evolutionary Psychology (BPS Textbooks in Psychology) Blackwell Chapter 4 – Mate selection ;
Workman., L. & Readrer., W. (2012) Evolutionary Psychology – An Introduction, Cambridge University Press Chapter 3 – Sexual Selection;
Buss, D.M. (2005) (ed) Handbook of Evolutionary Psychology, New York, Wiley;
Buss, D.M. (1989) Sex differences in human mate preferences: Evolutionary hypothesis tested in 37 cultures .Behavioural and Brain Sciences, 12 pp 39-49;
Buss, D.M. (2008) Evolutionary Psychology: The new science of the Mind. Boston Allyn & Bacon ;
Gangestad, S.W. & Thornhill R. (1997) The evolutionary psychology of extra-pair mating. Evolution and Human Behaviour, 18, pp69-88 ;
Gangestad S W & Simpson J. A. (2000) The evolution of human mating , Behavioural and Brain Science, 25, pp573-87;
Kokko, H., Brooks. R., Jennions. M.D. & Morley. J. (2003) The evolution of mate choice and mating biases. Proceedings of the Royal Society, B. Biological Sciences, 270, pp653-64;
Wesr, S.A., Lively. C.M., & Read. A.F. (1999) A pluralist approach to sex and recombination. Journal of Evolutionary Biology, 82, pp 327-48.
Only academic books and academic journals are excepted as references, so no magazines or newspapers please. The number of references will have to be around 25, no less than 23. Respecting the requests above will assure the essay will not be marked down. I will upload lecture slides later and I can be contacted at any time if needed.
Another very important comment I would make is about the focus of the paper. As differences between males and females in selecting their sexual partners can refer to any species on Earth, therefore it is a broad subject. For that reason, I believe the best way to approach the subject it to have a narrow focus and concentrate on the humans. That way, evolutionary strategies of both genders can be compared and contrasted as well as look at how did that change nowadays. Hope all this makes sense.
03/02/2015
1
The evolution of sexual
selection
Dr Carolyn Rice
Birkbeck, University of London Spring, 2015
Darwin’s Theory of natural selection
EVOLUTION
Occurs due characteristics
being inherited that are best adapted
to selective pressures.
EVOLUTION
Occurs due characteristics
being inherited that are best adapted
to selective pressures
NATURAL SELECTION
• Survival of the fittest
• Any trait that allows an organism
to survive in their physical
environment will become more
exaggerated over
evolutionary time
.
Why did the peacock worry Darwin?
Why do male stags have big antlers?
Darwin noticed his theory of natural
selection was not complete …..
} Many physical and behavioural
characteristics are difficult to
explain via natural selection
} Ms are larger & more decorated
} e.g. Stags – large antlers are a physical
disadvantage / Peacocks – long tails
hinder survival
} Problem – requires more effortful,
attracts predators etc.
} Ms engage in more risk taking
behaviour
} e.g. Stags fight for the right to be the
dominant male and access females
} Threatens survival
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2
‘Descent of Man, and selection in relation to
sex’ (1871)
} Competition to mate takes 2 forms
} Ms have to compete for F attention
} Fs choose on the basis of ornamentation
and display
INTRASEXUAL
SELECTION
Competition within a sex for
access to opposite sex.
Generally Ms compete with
Ms to access Fs
Regarded as responsible for males
being aggressive and developing
weapons to compete with e.g.
Horns, antlers, greater musculature
INTERSEXUAL
SELECTION
Members of one sex
compete to attract the
attention of members of the
opposite sex (usually Ms
attracting Fs)
Regarded as responsible for
evolution of sexual ornamentation,
e.g. Brighter plumage, courtship
displays
Surely its not
a girlies job
to choose?
EVOLUTION
Occurs due characteristics
being inherited that are best adapted
to selective pressures.
Allows survival and reproduction.
NATURAL SELECTION
• Survival of the fittest
• Any traits that allows an
organism to survive in their
physical environment will
become more exaggerated
over evolutionary time
(until it is no longer useful)
Characteristics will therefore evolve
that increase the ability to survive
and thus have the
opportunity to reproduce
SEXUAL SELECTION
• Survival of the ‘sexiest’
• Any trait that increases reproductive
success in its social
environment will become more
exaggerated over evolutionary
time (until it is no longer useful)
Characteristics will evolve that increase
the access to reproduction
Why have sex at all?
} Sex is complicated, costly and needs explanation
} Some spectacularly perverse reproduction styles !
} Acarophenax (mites) lay eggs into their abdomen, where they hatch.
} The brothers impregnate their sisters, (inside the mother’s
abdomen)
} The brothers die and the sisters eat the mother.
‘Sex, my son’
said the
Marquis of
Chesterfield,
‘doesn’t last
very long and
is extremely
expensive’!!!
Many viable ways to reproduce
Asexual Fission – Parent produces offspring that is
genetically identical to themselves through
a process known as ‘fission’
Parthenogenesis – offspring develop from
unfertilised egg
Unicellular organisms and some
multi-cellular organisms e.g.
bdelloid rotifers
Sexual Offspring produced through joining of two
gametes.
Isogamous – gametes are the same size
Anisogamous – two strict sexes, gametes
of different size, one sex provides egg and
early parental care, the other provides
sperm
Isogamous – common in single
cell organisms e.g.algae
Anisogamy – common in multicell
organism e.g. humans
Obligate and
facultative sex
Capable of both sexual and asexual
reproduction.
Starfish
Simultaneous
hermaphroditism
All have both male and female genitalia.
Reproduce sexually – one partner taking on
each sex role
Hamlet fish
Sexual reproduction is complicated
and costly
} Recombination of genes disrupts
adapted gene combinations
} Wasteful – individuals effectively
‘throw away ‘ 50%’ of their genes with
each offspring
} Energy could have been allocated to
feeding / avoiding predators
} Time taken increases risk of predation
} Sexually transmitted disease threaten
survival
} Difficulty of finding a mate –
particularly problematic in small
populations
03/02/2015
3
What are the benefits of sex?
} Parthenogenesis is very
effective
} If parthenogenetic offspring
are equally fit as sexual
offspring the parthenogens
would replace the sexuals
within a few generations
} This does not happen & sex
is widespread throughout
animals and plants
} So what are the benefits of
sexual reproduction?
Fate of a sexual population
with 106 individuals into
which one parthenogenetic
female is introduced
Benefits of sexual reproduction
Group
Individual
Gene
from Maynard Smith & Szathmáry 1999
Benefits operate at different levels
– Benefits at the group level
} Sexual populations can evolve more rapidly
(Fisher, 1958)
} Recombined gene è greater genetic variability in
sexually reproduced offspring
} Adaptive traits are passed between generations
} Sex speeds up evolution
} Populations have lower risks of extinction
} Asexual populations accumulate deleterious mutations
} Muller’s Ratchet – Muller (1964)
} Sex gets rid of harmful mutations that
would otherwise build up in the population
Asexual reproduction Sexual reproduction
} Mutation passed to offspring.
} Offspring is at a reproductive
disadvantage (as are future
generations).
} No way to get rid of mutation
except by waiting for another
mutation to cancel it out
} Recombination of genes
creates genetic variance.
} Only around 50% of offspring
carry the mutation
} Increases the rate of evolution
& decreases the probability of
species extinction by
} increasing rate at which two
advantageous mutations
can be brought together
} increasing the rate at which
disadvantageous mutations
can be discarded
– Benefits at the individual level
} It pays an individual to produce viable progeny
} Ensure the survival of individuals gene pool
} Lottery ticket / Raffle model
} asexual reproduction is like buying 100 identical lottery tickets,
} sexual reproduction is like buying 50 different tickets
} Offspring are better adapted to a
changing environment Williams (1975)
} Sex safeguards against unpredictable, rapidly
changing environmental pressures
} Allows the creation of adapted
genotypes against coevolving parasites
} Red queen hypothesis – Van Valens,
(1973)
} Sexual reproduction offers protection
against pathogens and parasites
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4
} Alice meeting the Red Queen in Lewis Carroll’s
book Through the Looking Glass
“ in our country …..
you’d generally get
somewhere else – if
you ran very fast for a
long time as we’ve
been doing”.
“Now here, you
see, it takes all the
running you can
do, just to keep in
the same place. If
you want to get
somewhere else,
you must run at
least twice as fast
as that!”
} Parasites and hosts are in
a continual evolutionary
battle
} Parasites (bacteria, virus &
other microbial parasites)
evolve more rapidly than
their hosts
} Hosts produce variable
offspring so that they will
have resistance to parasites
} Need to ‘run as fast as
you can just to stay in the
same place’
} Daphnia
} Parasite Pasteuria Ramosa infects the body cavity of
Daphnia and castrates it
} parasites often castrate their hosts
} Species is doing well as they have developed genetic
variation for resistance
} Red Queen H predicts sex should be more
common when parasite pressure is greatest
} Which do species who can reproduce
sexually and asexually favour when parasite
pressure is high?
} Water snails (Potamopyrgus antipodarum) (Lively, 1987)
} Can reproduce both asexually & sexually
} Live in both:
} stable lakes (high in parasites) &
} highly variable streams (low in parasites)
} Frequency of sex directly correlates with
parasite levels
} Sex is common in lakes (high in parasites)
} Sex is not as common in streams (low in
parasites)
Potamopyrgus
antipodarum
} Benefits of gene diversity in
dealing with parasites
} Major histocompatibility complex
(MHC)
} Highly diverse complex of many
genes – up to 500 alleles
} Involved in the immune systems
recognition of parasites
} Common to all vertebrates.
} Highly diverse complexes è higher
immunity
} Animals prefer mates who are
genetically dissimilar – detected
via smell
} Human ‘smelly’ t-shirt study
(Wedekind & Furi, 1997)
} PPs prefer t-shirts worn by those
whose MHC was unlike their own
} Offspring have fewer harmful mutations
} Makes repair damaged DNA easier
} repair of single-strand damage often easy (depends on
the damage)
} repair of double-strand damage requires more than just
sex
03/02/2015
5
– Benefits at the selfish gene level
} Selection favours genes that undergo sexual fusion
} Maximises fitness – maximises the chance of
survival
Mating systems and sexual
selection
Mating systems
– Adaptive – changes in response to environment
MONOGAMY Exclusive M ; F
sexual bond
Preferred strategy of
Women – if male of good quality and provides
care for offspring
Men, if mate competition and resources do not
allow polygyny
POLYGYNY Form of
polygamy: One M
– multiple Fs
Prefered strategy of
Men – if resources and mate competition allow
it. Women – if the male has sufficient quality to
establish a harem and resources equal to those
in monogamy
POLYANDRY Form of
polygamy: One F
– multiple Ms
Rare system. Occurs in harsh conditions
where resources of more than one males may
be needed for offspring care
PROMISCUITY Males and
females have
multiple shortterm
matings
Occurs when plentiful environmental conditions
allow single maternal carer but competition
between males cannot guarantee exclusive
access (sperm competition may occur)
Consequences of Anisogamy
(Gametes of different size)
} Fs invests more energy in reproduction than Ms
} Eggs are expensive, sperm is cheap
} F pays almost all the costs but only gets 50% of offspring
Ovum – very large
& energy rich; long
lived; limited in
number
Sperm – very small
& numerous; short
lived; rapidly
renewed
Can produce
offspring with
many women
in a short time.
Low energy
investment in
each gamete
Does not carry
offspring
Can produce
offspring with
one man at a
time
High energy
investment in
gamete
Carries
offspring for 9
months
} Variance in reproductive success drives
intersexual selection
} Fs have lower potential for
reproductive success over a lifetime
} Adopt a quality strategy
} Fs choose from the Ms on offer
} Variance in reproductive success drives
intrasexual selection
} Ms have potential for higher
reproductive success over a lifetime
} Less choosey – adopt a quantity
strategy
} Ms compete to be chosen by Fs
}
03/02/2015
6
} Do these competitive strategies hold under all conditions ?
} Effect of food availability on intersexual competition
} Ms competing & Fs choosing
} Katydids males contribute nourishment to the females in
their sperm
} Food abundant environments
¨Fs can get food from other sources
¨Fs are choosey ; Ms compete
} Food scarce environments
¨Fs fight over the males
– Batemans principle (1948)
} ‘M reproductive success increases with
each additional partner mated to a
greater extent than is true for Fs’.
} Variance in reproductive success is greater
for Ms than Fs
} Fs can always find a mate with but have an
upper limit on how many offspring she can
produce
} Ms have almost no upper limit but are faced with
choosey females who only mate with the best
specimens
Red Deer – M 0-23 offspring Mean 5.41(Variance 41.9)
Red Deer- F 0-9 calves Mean 5.03 (variance 9.09)
(Clutton – Brock, 1988)
Variance in reproductive success drives
physical characteristics
} Differences in M : F body size
} Variance in M : F reproductive success drives sexual dimorphism
} Ms need larger bodies for combat
} Larger bodies come with energy cost
} Degree of difference in M : F body sizes are linked to:
} Degree of competition needed by Ms to secure a F
} The size of the harem that needs controlling
Elephant seals
} Male : female ratios
} Body length = 1.6 : 1
} Weight – male = 4000 pounds ; female 850 pounds
} The life of a male elephant seals
} 9 months storing food
} 3 months hauled up on a beach, trying to protect a harem of 40 –
50 females from other males, who he will fight vigorously with,
which is not easy as he is designed to swim not run.
} Juvenile males try to sneak copulations.
} Controlled chaos that goes on for three months – becomes
exhausted fighting.
} Male ornamentation
} Ms need to catch the attention of Fs
} Ms of many species have characteristics that serve to attract
females (e.g. brighter colouration, exaggerated tails)
} Does ornamentation serve to
attract Fs?
} Since 1960s evidence has grown
for the direct influence of Fs on M
physical features and reproductive
success
} Male courtships
03/02/2015
7
} African Widowbird – Kenya (Anderson, 1986)
} Fs – mottled brown / short tails
} Ms – jet black with red epaulettes / long tails
} Pre-study measures
} number of nests in a territory (location of nest
selected by Fs)
} size of territories (determined by the M)
} Manipulation – changed length of tail feathers
} Extended tails
} Reduced tails
} Controls
} Findings
} No change in the size of male territories
} More nests in the territories of bird with long
tails by a ratio of 4:1
} F preference for long tails increased M
reproductive success
} Peahens (Petrie et al., 1991)
} F prefer to mate with
peacocks with tails that had
not been reduced in length,
or that had not had the
decoration obscured
} Guppies (Haines & Gould, 1994)
} Ms have different tail lengths
} Longer tails slow them down
} F spend more time & mate
more often with Ms with
longer tails
Are M adornments a sign of sexiness or
a sign of good genes?
Gene advantage theories Sexy sons theory
Handicap theory
(Zahavi, 1975)
Parasite theory (Hamilton
& Zuk, 1982)
Runaway selection
theory (Fisher, 1930)
-Male adornments
develop as an
impediment to
demonstrate genetic
superiority/ survival
abilities despite having
a handicap (not to
look attractive
-Females choose
males who show
conspicuous and
costly adornments as
this is a sign of
genetic quality
-Male adornment
evolved to display
lack of parasites
which signifies
genetic superiority
i.e. ‘healthyoffspring’
-Females chose
male features that
demonstrate a lack
of parasites and
hence genetic
quality
– Fs prefer
attractive male
adornments as
they suggest an
ability to produce
‘sexy sons’
-‘Sexy sons’ are
more desirable &
are more likely to
find a mate of their
own – so
Fs genes survive
Good genes or sexy sons?
} Good genes
} Supported by many studies show offspring of highly
ornamented Ms survive better
} Sexy sons
} Supported by many studies show Fs prefer Ms who are
more highly ornamented
} Swallows
} Fs swallows prefer males with longer tail feathers
} Ms with longer tail feathers flew better in tests in wind tunnels
} Length of tail feathers were both :
} increase attractiveness of males
} direct indicators of good genes
Theories are not mutually exclusive
The role parental investment in
determining who competes and chooses
} Parental Investment (Trivers, 1972, 1985)
} Total cost of reproduction is more than the gamete cost
} Sex with lower investment competes
} Sex with higher investment chooses
Penguins Males Females
Investment pre-birth Low High
Investment post- birth Equal Equal
Consequence Similar size to Fs.
No more ornamented.
Pipefish Males Females
Investment pre-birth Greater. F transfers egg to M
pouch. Ms carry eggs until
they hatch
Little
Investment postbirth
Not applicable Not applicable
Consequences One brood from one F. Up to 4 broods with 4 males.
Those most successful in mating are
larger and more ornamented.
Elephant seals Males Cows
Weight 3,000 kg 650 kg
Investment pre-birth Few grams sperm Pup weights 50kg
Investment postbirth
None – spends time fighting other
males to mate with other females
Substantial – in first 5 weeks of life
pup gains 100kg / cows lose 200 kg
Consequence Larger, more ornamented , compete Choose
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Extra-pair mating
} Parental investment view is oversimplified – monogamy does
not always rule!
} Batemans theory states…..
} Benefits of extra-pair mating is greater for Ms than Fs
} Does not state there is no benefit to Fs
} Why do F undertake extra-pair mating
} Best Ms may have been paired when F formed her pairbond
} Its better to accept a low quality than none
} Even low quality partners help defend territory & aid parenting
} Opportunity to be fertilised by higher quality males, better
genes = better offspring
} Extra-pair copulation in Blue Tits (Cyanistes Careuleus)
Kempenaers et al (1997)
} Low quality Ms partners (sang shorter song) lost paternity to
superior extra-pair Ms (sang longer songs)
} DNA tests show 30 – 50% of nests contained eggs fertilised by
a M that was not the social partner
} Offspring of extra-pair Ms were more likely to survive
Sperm competition in extra-mating
situations
} M need to ensure that they are the one to
fertilise the F. Large testes are an advantage
} More likely to result in fertilisation as sperm from 2 or
more males will complete in the uterus.
} Testes size correlates with F promiscuity
} Chimps – large testes
} Fs highly promiscuous
} Ms physical aggressive
} Gorillas – small testes
} Large dominant male defends a harem of Fs.
} Fs not promiscuous – no sperm competition.
} Little M physical aggression
Human sexual selection
} Does Bateman’s principle hold in humans?
} Is the variance in M reproductive success greater than F
reproductive success?
} UK M success is 6% higher than F
} Cross cultural studies – M reproductive success is higher than F
BUT Local economic and social situations may modify
the extent of the difference
Aggression & Sexual Dimorphism
} Ms more likely to be aggressive
} M deaths from violence peak between 16-25 years.
} Ms approx 10% larger than Fs
Parental Investment?
Humans Females Males
Size 10% larger
Gamete cost Few, larger, high cost eggs
(1,000, 000 larger than sperm)
Provides almost all material for
early development
Many, small, low cost sperm
(DNA plus tails!!)
Rearing
investment
Generally invest much more. High
gestation cost. Human infants born
immature & need much support –
lactation, general nurturing.
Generally, cost is much lower.
Could desert mate but
generally ‘stick around to
ensure ‘gene’ survive
Consequence
of making
poor mating
decisions
Pay a heavy price for poor choices,
so need to be choosier
Lose little from poor choices
in terms of evolution but may
result in increased demands
on resources and time.
03/02/2015
9
Why are humans relatively
hairless?
– Enabled our ancestors to
keep cool through sweating
to aid survival (adaptation
through natural selection)
– Allowed humans to
‘advertise’ their reduced
susceptibility to parasitic
infections – desirable trait
in a mate (adaptation
though sexual selection)
Signs that Ms have good genes and are
parasite free? Human sexual selection characteristics
} Sexual selection characteristics evolved
in the ‘Environment of Evolutionary
Adaptiveness’ (EEA)
} around 5 million years ago
} Mate choice based on characteristics
important at that time
} Good genes – survival
} Good traits – will be passed to offspring
} Good parents – support offspring upbringing
} We are pre-programmed to attend to
characteristics that indicate
} fertility (likelihood of reproduction)
} viability (likelihood of survival)
Buss
} Extensive questionnaire survey – 10,000 PP
} Cross-cultural (37 cultures)
} Uncovered
} species specific preferences (important in terms of evolution)
} culture specific preferences
Preferred characteristics in long term mates
by gender
Gender differences in long-term mates
– Female preferences
} Good earning capacity / good education
} Provision of gifts is common in many species
} Indicators of ability to provide are attractive to women.
} In our evolutionary past – Sex-for meat’ (Fisher, 1992)
} Modern day polygamous societies
} Best hunters with most resources:
¨ have the most wives
¨More likely to have extra-marital affairs.
} Provisioning less important when Fs are fairly independence
(e.g. Holland)
Gender differences in long-term mates
– Male preference
} Good looks
} Both Ms & Fs show a clear preference for good
looks but Ms rate this more highly in a partner
} Some cultural differences but generally M
preferences are universal and correlates with
youthfulness (signals high levels of hormones
necessary for fertility)
} Large eyes
} Good teeth
} Lustrous hair
} Full lips
} Small jaw
} Low hip- waist ratio (hour-glass figure)
03/02/2015
10
‘False’ indicators …..
Bustle Dress
©2005 University of Utah
‘Honest’ indicators
} ‘Honest indicators of good genes in Fs
} Facial symmetry
} Good skin
} ‘Averageness’ – close resemblance to the majority –
indicates a low likelihood of genetic mutations.
} Honest indicators of good genes
in Ms
} Fs are attracted to men with
masculine features such as
large jaw and prominent
cheekbones (Grammer & Thornhill, 1994)
• Links to high testosterone.
• Testosterone dampens the
immune system so only a
healthy individual can afford to
produce these traits. (Thornhill &
Gangestad, 1999)
Chastity & Extra-pair Mating
} Preference for chastity in long term
partners – relatively low importance list
for both but more important for Ms
} M – possibility of cuckoldry
} Fs – know who the father of any
offspring is
} ‘Between’ and ‘within’ cultural
differences in sexual permissiveness
} Countries which are most relaxed tend
to have financially independent Fs
Extra-pair couplings
Cross-culturally?
– Ms would like to mate with more partners over time but Fs are
exclusively monogamous.
– Opens up the possibility that a male may be cuckolded and
consequently waste his parental investment
East Asia
South/SE Asia
Oceania
Africa
Middle East
Southern Europe
Eastern Europe
Western Europe
South America
North America
% Desiring “More Than One” Sex Partner
40
30
20
10

Men
Women
“Ideally, how many different sexual partners would you like to have in the future?”
Source: Schmitt et al. (2003, Journal of Personality and Social Psychology)
03/02/2015
11
Percent of PPs who agreed when approached by an
opposite-sex stranger – Clark and Hatfield, 1989
Women ~50%
Men
Go on a date tonight Go to bed with me tonight

~50% 75%
Men see an invitation for casual sex as a compliment and an opportunity to
produce extra offspring at little cost
Women see it as a threat and an insult – they have far more to lose! -3
-2
-1

1
2
3
5 years
2 years
1 year
6 mo
3 mo
1 mo
1 wk
1 day
1 eve
1 hr
Likelihood of Intercourse
women
men
Likelihood of Agreeing to Have Sex With Someone
You Find Attractive as a Function of Time Known
– Ms slightly disinclined to have intercourse with a woman they had
known for just a week.
– Fs slightly disinclined to have intercourse with a man they had known
for less than three months (Buss& Schmidt (1993)
Pros and cons of extra-pair mating
Males
Females
} Disadvantages
} Sperm cost (minimal)
} Pre-mating costs
} Risk of attack due to sexual jealousy
} May reduce chance of offspring
survival as may not be able to
provide for them
} Advantage
} Opportunity to produce extra
offspring at little cost
} Disadvantages
• Unlikely to increase number of
offspring
• Desertion
• Violent retribution from partner
• Damage to reputation (less
marriageable)
} Advantage
} Material support
} Genetic variability
} Sexy sons
Sexual selection and brain development
} 1 – 2 million years ago our brains tripled
in size. Miller’98 suggested this was
due to sexual selection.
} Needed to develop problem solving
and manual abilities to support
competition
} Need for potential mates to provide
increasingly creative displays
Bonobo brain
Human brain
Overview
} Sexual vs. natural selection
} Why sexual reproduction?
} Mating systems
} Inter- and intra-sexual competition
} Parental investment
} Extra-pair mating
} Human sexual selection
} Lon-term relationships
} Short-term relationships
Suggested viewing
} Excellent PBS programme on sexual selection
} http://www.youtube.com/watch?v=JakdRczkmNo