Transcript Chapter 5

Chapter 4
Human Mate Choice
Mate Selection
• Choosing for:
– Genes
– Parenting
• Looking for:
– Underlying “universals”
– Individual preferences
Male/Female Pressures
• Females
– Choosier than males
– Higher reproductive costs
– Greater emphasis on child support
• Males
– Somewhat choosy (especially compared to non-human
primates!)
– Lower reproductive costs
– Greater emphasis on mating
• Interbirth interval
Male Parenting Investment
• Can the male improve the female’s rearing
success?
• If yes, selection favours males that help rear
• If no, selection favours males that have
many matings
Quality and Quantity
• Quality: fewer, higher caliber offspring
• Quantity: more, lower caliber offspring
• Sometimes stated that males favour quantity
and females quantity
• This is an oversimplification to be avoided
• Comes down to differential reproductive
success
Life-History Factors
• Brain size correlates with life-history
factors (age of weaning, sexual maturity,
gestation length, longevity)
• Species with big brains tend to stretch out
life-history factors
Brains
• Human
– 1.4 kg brain, 65 kg body
– 0.0215 brain/body
• Monkey
– 0.1 kg brain, 7 kg body
– 0.0143 brain/body
• Baboon
– 0.14 kg brain, 30 kg body
– 0.0047 brain/body
Gestation Length
• Homo sapiens, average brain capacity of
1350 cc
• Comparison to other primates
• Humans should go 21 months, not only 9
• Humans have a year’s worth of growth to
“catch up on” when born
Brain Size
• Newborn ape’s brain about 200 cc, roughly
half that of an adult’s
• Newborn human’s brain about 450 cc,
roughly a third the size of an adult’s
• Both ape and human brains reach adult size
early in life, but apes’ brains only have to
double, not triple in size
• Brain of 675 cc would make human head to
large to birth
Birthing Complications
• Maternal and infant survival
• Head size vs. pelvis
– Birth vs. bipedal locomotion
• Menopause
– “Grandmother hypothesis”
Ancestral Brain Growth
• Humans departed from apelike growth
when adult brain passed about 770 cc
• Beyond this, brain would have to more than
double from birth
• Beginning of helplessness in infants
• Essentially, premature birth
• Homo habilis, 800 cc brain
• Homo erectus, 900 cc brain
Developmental Waypoints
• Human childhood prolonged compared to
apes
• Slower physical growth
• Tooth eruption later than in apes
1st molars
2nd molars
3rd molars
Human
6
11-12
18-20
Chimpanzee
3
7
9
Growth Rate and Similarity
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•
•
•
Holly Smith, U of Michigan
Correlating growth rate with tooth eruption
Australopithecines’ growth pattern ape-like
Early Homo erectus’ (pre 800 k) growth
pattern intermediate between apes and
modern humans
• Late H. erectus’ (post 800 k) growth pattern
like modern humans (and Neanderthals)
Parental Certainties
• Female
– Always certain
– Maternal certainty
• Male
– Never certain
– Paternal uncertainty
• Descriptions of child’s appearance
– Maternal relatives
– Paternal relatives
Certainties
F -- M
Y/N
Y/N
M -- F
Y/N
M -- F
Y/N
M -- F
Y/N
F
N/N
M -- F
Y/N
M
N/N
M -- F
M -- F
N/N
N/N N/N
N/N
N/N
N/N
F
M F
M
F
M
Cryptic Oestrus
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•
•
•
Concealed ovulation
No obvious physical indicators of oestrus
Different from other primates
Males can’t be sure when females are able
to conceive
Why Have Concealed Ovulation?
• Increase paternal certainty
– Also increase chance of pairbonding
• Decrease paternal certainty
– Reduce infanticide
• Allows females to secure more courtship
gifts
• Prevent females from avoiding pregnancy
Examples of Human Sexually
Selected Traits
• Males
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–
–
–
Beards
Voice
Upper body
Height
• Dominance
• Females
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–
–
–
–
WHR
Large eyes
Shiny hair
Full lips
Small jaw
• Youthfulness
Two Perceptions of Beards
• Negative perceptions of increased
recklessness, dirtiness, lower mental
competence and lower intellectual ability,
reduced social maturity and reduced
physical attractiveness
• Positive perceptions such as masculinity,
strength, intelligence and desirability
Reed & Blunk (1990)
• Facial hair positively contributes to
perceptions of social/physical
attractiveness, personality, composure and
competency.
A: attractiveness
B: personality
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C: Competency
5
D: Composure
4
be ard
mus tach
cle an s have n
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A
B
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D
Beards: Cheating
• Males lacking dominant, desired appearance
may use beard
• Hide expressions of emotions, to protect the
dominant image
• Disguise weak chin, skin damage
Male Status is Attractive
• Sadalla et al. (1987)
• Female subjects watched silent video of two
men interacting in office environment
• More dominant male judged to be of higher
status and more attractive
Male Ambition/Dominance
• Buss (1989)
• Ambition and industriousness valued
• Resource potential
Waist-toHip Ratio
• Singh (1993)
• Underweight,
normal,
overweight
• 0.7 to 1.0 WHRs
Stimuli
Results: Young Subjects
Results
• Generally, similar male and female patterns in
rankings
• Used both WHR and body weight to rank
• Within weight category, subjects systematically
used WHR to infer all attributes
• Overall, higher ratings for normal weight than
under- or overweight figures, and for 0.7 WHR
across weight categories
Marilyn
Monroe
www.topnews.in/light/f
iles/MarilynMonroe.jpg
Gong Li
www.hicelebs.com/gal
lery/gong_li/5.html
Kate
Moss
www.eforu.com/galler
y/katemoss/pic62.html
Venus De milo
webpages.ursinus.edu/classics/zzp
ictures/venus_de_milo.jpg
Android and Gynoid
• Body shapes
• Testosterone: stimulates fat deposits to
abdomen and inhibits deposits to
gluteofemoral regions
• Estrogens: inhibit fat deposits in
abdomen and maximally stimulate
deposits to gluteofemoral region (and
other regions, too)
• Altering sex hormones alters fat
distributions and body shape
• Age indicator: highly different between
children and elderly
• “Honest signals”
Image modified from Pioneer Plaques
http://www.nd.edu/~jmontgom/ti/GraphicArchive/
Scans/Original%20Files/Pictograph/PioneerPlaque.jpg
Female/Male Dimorphism
• Not a simple preference for female WHR=0.7
• Cross-cultural WHR data
– Resource availability, re: fat storage
– Front vs. side view
• Non-overlapping
American blacks
Male
0.84
Female
0.75
American whites
0.82
0.73
Mexican-Americans 0.94
0.84
Moost (Mongolia)
0.76
0.85
Symmetry
• Phenotypic depiction of genotype
– Bilateral symmetry
• Fluctuating asymmetry
– Small, random differences
• Genotype and environment
• Immune system
• Sex hormones
Age Preferences
• Buss (1989) cross-cultural survey
• Men prefer younger women (average 2.66
years)
• Women prefer older men (average 3.42
years)
Reproductive Value and Fertility
• Fertility
– Current probability of successful reproduction
• Reproductive Value
– Age-specific future likelihood of offspring
production
– Future expected reproductive success
– Average lifetime reproductive success
Terms
• Monogamy
– Long-term pairbond with one mate
• Polygamy
– Polygyny: male with multiple female mates
– Polyandry: female with multiple male mates
• Promiscuity
– Males and females mate with multiple shortterm partners
Savanna Baboons
• Males leave birth troop and join another
troop nearby
• Males about twice the size of females
• Males not related to other males in troop, so
no kin selection to ameliorate male-male
competition for mates
Common Chimpanzees
• Males stay with troop they’re born to,
females leave (don’t know why)
• Males maintain kinship with other males
• Leads to male-male alliances and bonds
• Male cooperation reinforced by kin
selection
• Hunting, troop protection, female
acquisition
Bonobo Chimpanzees
• Females also more likely to leave to join
another troop
• However, very different alliance and
bonding pattern in bonobos vs. common
chimpanzees
Size and Structure
• For both chimpanzees and bonobos, males
bigger than females by about ~25%
• Close to modern humans
• In chimpanzees, like savanna baboons,
males dominant over females
• In bonobos, smaller females seem dominant
over males
Humans
• Culture
– Most allow for polygamy
– Monogamy common (obligate or facultative)
• Testis size
– Bigger if polygamous
– Sperm competition
• Sexual size dimorphism
– Greater M/F difference --> more polygamous
Primate Social Organization
female
Gibbon
Gorilla
monogamous couples
polygamy
male
Chimpanzee
Bonobos
Orangutan
solitary lives; several
females within a male’s
territory
Adapted from: de Waal (2006)
promiscuity; strongest
bonds between males to
hunt and protect
territory
Humans
promiscuity; strongest
bonds between females,
but females also bond
with males; male’s
status dependent upon
mother’s
monogamy,
polygamy,
polyandry,
promiscuity
(In)Fidelity
• Monogamy, polygamy, polyandry, and
promiscuity
• Male infidelity
– Additional offspring
– Low investment cost
• Female infidelity
– Access to better genes
– Resources from long-term mate
Infidelity
• Women
– Cheat more when reproductively receptive
– Appearance
– Risk taking male for one-night stand, not longterm relationship
• A major concern for males
– Genetic altruism
Attitudes
• Buss (1989)
– Males value virginity and chastity in women
more than women do in men
• Buss & Schmitt (1993)
– American men rated “faithfulness” and “sexual
loyalty” as most highly valued traits in woman
for long-term relationship
Emotional vs. Sexual Infidelity
• Harris (2000)
• Women more bothered by emotional
infidelity
– Across studies, 62-86%
• Men more bothered by sexual infidelity
– Across studies, 47-60%
Children from Previous Relation
• Step-parenting
• Investing resources in non-biological
offspring
• Detractor
Reality Television
History
• Long history (eg. Candid
Camera)
• MTV’s Real World in 1992
• Very popular
– Final episode of Survivor
(2000): 51,000,000 viewers
– Survivor: Palau premiered to
23.66 million viewers on
Thursday, February 17
www.erzwiss.uni-hamburg.de/ personal/gramlinger/
Finding a Mate Shows
• Long-term (e.g., Bachelor(ette)) or shortterm (e.g., Elimidate) mating strategy
• Resources
• Attractiveness
• Fidelity
gsep.pepperdine.edu/.../ fall2003/reality-tv.htm
Long-term Mating Strategy
Shows
• More than one episode
• Generally males don’t blatantly
display resources
• Cast appears “classier”
• Winner is supposed to be a
husband or wife, not a “fling”
http://www.espn.com
Short-term Mating Strategy
Shows
•
•
•
•
Usually a single episode
Women show more skin
Men explicitly show resources
Both sexes often deceive by withholding
truth or lying
http://www.knws51.com
Picking a Long-term Partner (Both
Sexes)
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Schmitt & Buss (1996)
Act helpfully, honestly, kindly, sensitively
Become friends
Communicate
Invoke love and show commitment
Call rivals exploitative, selfish, and
insensitive
Female Attracting Male (LongTerm)
• Display sexual exclusivity
• Question rival’s fidelity
Male Attracting Female (LongTerm)
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Display resources
Demonstrate commitment
Derogate rival’s achievements
Derogate rival’s resource potential
Suggest rival lacks goals
Picking a Short-term Partner
• Buss & Schmitt (1993)
• Females maintain higher standards
• Males more likely to accept minimum
criteria for casual sex
– Males reject women with indications of low sex
drive, prudishness, and desire for commitment
• High promiscuity favoured for short-term
but not long-term partner
Female Attracting Male (ShortTerm)
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•
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•
•
Act flirtatious and seductive
Sexualize appearance
Make a sexual proposition
Downplay intelligence
Have sex
Call rival sexually unavailable
Male Attracting Female (ShortTerm)
• Give resources immediately
• Machismo
• Display dominance, confidence, and
resources
• Show-off
• Derogate rival’s resources
Male Success in Bachelorette
• Men often describe themselves as
“intelligent,” “ambitious,” and reference
their resources
• Greatest Achievements:
– “Owning my own home and business.” Chris C.
(Bachelorette 3)
– “Graduating from Stanford Business School
while starting companies along the way.” Chris
M. (Bachelorette 3)
Success
• In Bachelorette favoured
men are generally relatively
successful
– Lawyers, business executives,
sports agents, etc.
• Bachelors typically
extremely successful and/or
heirs to fortunes
– e.g., Andrew Firestone
(Bachelor 3)
http://www.abcactionnews.com/entertainment/stories
/0305/030518bachelor.shtml
Success
• In Bachelor, most women are less
successful
www.rugged
elegantliving.
com/sf/a/002
338.html
– Students, service industry
• Bachelorettes are fairly successful,
but lower status than male
counterparts in Bachelor
– e.g., Meredith (Bachelorette 2) was a
make-up artist
– However, in Bachelorette 4, DeAnna
Pappas is real estate agent and winning
man, Jesse, a professional snowboarder
abc.go.com/primetime/bachelorette/index?pn=photos#t=109339
Age Range
• Bachelorette 3 (25 men, 1 woman)
– Jen, the bachelorette, was 28
– Average of men was 30 (range 25-37)
• Bachelor 6 (26 women, 2 men)
– Byron and Jay, the bachelors, were both 40
– Average age of women was 32 (range 27-39)
Attractiveness
• Most women in reality TV are considered
average or above average in appearance
• This is what men favour (e.g., Buss 1989)
• Male physical attractiveness on reality TV
is not as consistent
• This is also the pattern predicted by EP
Personality
• Some men gain popularity via personality
• Bob (Bachelorette 1), slightly overweight,
won female fans because of genuineness
and sense of humour. He became the
bachelor for Bachelor 4.
• Adam Mesh (Average Joe 1) was so popular
with female fans he got his own show.
Average Joe: Adam Returns
www.realitytvworld.com/averagejoe3/
Samantha
sales-clerk
socialite wannabe
not into deep thinking
Rachel
elementary teacher
likes kids
Adam’s mom’s pick
Fidelity and Children
• 9/25 and 12/25 men stated they
were “loyal,” “trustworthy,” or
“honest” in Bachelorette 1 and 3,
respectively
• On Bachelor 2 Aaron was
bothered that one of the final 3
women (Gwen) had been
previously married; he didn’t pick
her
• On Average Joe 3 Adam
eliminated Brittany when she told
him she had a 6 year old son,
stating it would add one more
element to the relationship
www.gwengiolia.com
www.wchstv.com/abc/
thebachelor/
community.realitytvworld.com www.realitytvplanet.com