Anthro 101:
Human Biological Evolution
Lecture 8: Human Mating Behaviors
Human Mating Behavior
• How do we select our
mates?
• What makes a good
mate?
• How has this process
changed in a modern
w...
One of the most important adaptive problems
that humans face is: Who is a good mate?
• Choosing a good mate is closely lin...
In choosing “good” mates, individuals have to
avoid kin
Nonhuman primates
• one sex leaves the original troop
• Avoid mati...
Beyond the incest taboo (cultural rules), we have
evolved mechanisms for avoiding inbreeding
• Must solve the problem of k...
Westermarck effect: a mechanism identifying kin
• Two people who live in close domestic
proximity during the first few yea...
Evidence for Westermarck effect: Sim-pua
• sim-pua marriages in Taiwan
• Poor families would arrange
marriage for daughter...
When bride adopted into family later, couples end
up with more children on average
Kibbutzim in Israel (J. Shepher):
• Agricultural collectives
• Children raised communally
by childcare specialists
• Unrel...
Evidence for Westermarck Effect: Lebanon
In Lebanon, cousin marriage is practiced
• Brothers often live in same household
...
Patrilateral parallel cousin marriages are less
successful than other marriages
• Patrilateral parallel cousins are raised...
Cues ≠ Facts
• Mechanism does not detect actual kinship
• Uses childhood cohabitation as a cue to kinship
• In the past, c...
Another cue: Humans may be able to detect
genetic similarity through olfactory cues
• MHC = major histocompatability compl...
Experimental evidence suggests humans respond
to MHC “odor” cues when choosing mates
• Assess MHC type for male and female...
Women’s perceptions of male smells depend
on MHC and hormonal status
0
1
2
3
4
5
6
7
8
Not on Pill On Pill
PleasantnessRat...
Studies of Hutterite population also suggest
that MHC affects mate choice
• Hutterites are a small
Anabaptist community in...
The relationship between inbreeding
avoidance (biology) and incest rules (culture)
is not always clear
• If aversions to i...
Behavioral Ecology & Mate Choice: The Kipsigis
• Farmers & herders in Kenya
• Wealth measured as:
• Amount of land owned
•...
What makes a desirable Kipsigis husband?
• Wives are given a plot of the husband’s land
• Women with larger plots
• Can gr...
What makes a desirable Kipsigis wife?
• Men have many wives
• some men get none =
competition for women
• Bridewealth paym...
What makes a desirable Kipsigis wife?
• Early maturing women bring higher bridewealth
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0....
What makes a desirable Kipsigis wife?
0.3
0.32
0.34
0.36
0.38
0.4
0.42
0.44
Cohort 1 Cohort 2 Cohort 3
LiveBirthsperYear
E...
What makes a desirable Kipsigis wife?
• Plump women - with plenty
of nutrition & no disease -
also bring higher bridewealth
Evolutionary psychologists also explore
factors that affect mate choice
• Adapted to choose mates who enhance our
reproduc...
As a pair-bonding species, we also predict
similarity in mating strategies & preferences
• Able to produce many healthy ch...
Evolutionary psychologists predict that
women’s mate choice criteria will be related
to resources
• Human infants require ...
Male mate preferences are expected to be
based on female fertility
• Male mating success depends on reproductive success o...
Both males and females must be concerned
about fidelity, but this may matter more to
males than females
• For females
• If...
Evolutionary psychologists predict that
similar preferences will exist in all societies
Sample mate choice criteria in 37 ...
Preference for good financial prospects
0
0.5
1
1.5
2
2.5
3
Japan Zambia Yugoslavia Australia USA
MeanRating
Men
Women
Ind...
Preference for good looks
0
0.5
1
1.5
2
2.5
3
Bulgaria Nigeria Indonesia W Germany USA
MeanRating
Men
Women
Unimportant
In...
Males Females
1. Good health
2. Mutual attraction and love
3. Good looks
4. Emotional stability and maturity
5. Dependable...
However, the cross-cultural data also show
that men and women care most about
character
Trait Males Females
Mutual attract...
Men and women BOTH value the traits that
would contribute to long-term unions
• Human children require extended
period of ...
There is also considerable cross-cultural
variation in preferences
Preferences about chastity are most variable
Preference...
Conclusions
• In general, BOTH men and women want:
• Mutual attraction, Love
• Kindness, pleasing disposition, humor
• Emo...
After a long evolutionary history…where are
we as a species?
• We are adapted to be flexible
in our behavior
• We are adap...
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Lecture 8 human mating behaviors

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Lecture 8 human mating behaviors

  1. 1. Anthro 101: Human Biological Evolution Lecture 8: Human Mating Behaviors
  2. 2. Human Mating Behavior • How do we select our mates? • What makes a good mate? • How has this process changed in a modern world?
  3. 3. One of the most important adaptive problems that humans face is: Who is a good mate? • Choosing a good mate is closely linked to fitness • Avoid mating with kin • Prefer mates who are likely to reproduce successfully • Evidence of special design to fulfill these functions • Avoid inbreeding • Choose someone of high quality • Compatibility is important
  4. 4. In choosing “good” mates, individuals have to avoid kin Nonhuman primates • one sex leaves the original troop • Avoid mating with close kin • Chimp females avoid brothers • Baboons avoid age-mates (likely half brothers through father) • Rhesus macaques avoid kin Human Societies • Lots of different mating systems • None allow regular mating between siblings or parents • Rules, customs to prevent close kin from mating
  5. 5. Beyond the incest taboo (cultural rules), we have evolved mechanisms for avoiding inbreeding • Must solve the problem of kin recognition • Mothers easily know offspring • Fathers is harder in many cases • Siblings… • Westermarck effect • Phenotypic similarity
  6. 6. Westermarck effect: a mechanism identifying kin • Two people who live in close domestic proximity during the first few years in the life of either one are desensitized to later sexual attraction • cohabitation as a cue • Critical period in the first 5 years of life • turns “off” attraction between same age siblings, caregiver and child • higher reproduction / survival rate than those that where attraction not “off”
  7. 7. Evidence for Westermarck effect: Sim-pua • sim-pua marriages in Taiwan • Poor families would arrange marriage for daughters at birth • Girl is raised in future husband’s household • Bride and groom raised like siblings • Sim-pua marriages were problematic • Lack of sexual interest • Low fertility • More infidelity • More divorce
  8. 8. When bride adopted into family later, couples end up with more children on average
  9. 9. Kibbutzim in Israel (J. Shepher): • Agricultural collectives • Children raised communally by childcare specialists • Unrelated individuals raised together in Kibbutzim show diminished sexual attraction to each other • Of 2,769 marriages in 211 kibbutzim, only 14 between members of same peer group, and all but one joined after age 6 Evidence for Westermarck: Kibbutzim
  10. 10. Evidence for Westermarck Effect: Lebanon In Lebanon, cousin marriage is practiced • Brothers often live in same household • Families of brothers are very close • Offspring of brothers grow up much like siblings • Ideal marriage = patrilateral parallel cousins Patrilateral parallel cousin Patrilateral cross cousin male female
  11. 11. Patrilateral parallel cousin marriages are less successful than other marriages • Patrilateral parallel cousins are raised in close association • Patrilateral cross cousins are NOT raised in as close association • Marriages between patrilateral parallel cousins are less successful than marriages between patrilateral cross cousins • 23% fewer children • 4 times as likely to divorce • Less sexual attraction
  12. 12. Cues ≠ Facts • Mechanism does not detect actual kinship • Uses childhood cohabitation as a cue to kinship • In the past, cue was probably right often enough • Can be wrong • siblings raised apart are more likely to have a relationship when they meet, even though they are genetically related • Adopted siblings, step parents not interested in each other
  13. 13. Another cue: Humans may be able to detect genetic similarity through olfactory cues • MHC = major histocompatability complex • Part of immune system • Linked to disease resistance • MHC is hypervariable genetic marker • Kin share similar MHC markers • Mice prefer mates with MHC unlike themselves • Could be adaptation to enhance pathogen resistance • Could be adaptation to prevent inbreeding • Humans can distinguish (by smell) mouse strains that differ only in MHC
  14. 14. Experimental evidence suggests humans respond to MHC “odor” cues when choosing mates • Assess MHC type for male and female subjects • Males asked to wear T-shirt for 2 nights • Asked not to smoke, use deodorant or cologne • Try to maintain “odor neutral” environment • Women were asked to rate smell of T-shirts worn by men • Pleasantness • Sexiness • Intensity
  15. 15. Women’s perceptions of male smells depend on MHC and hormonal status 0 1 2 3 4 5 6 7 8 Not on Pill On Pill PleasantnessRating Dissimilar MHC Similar MHC • Women not on hormonal birth control • find men with dissimilar MHC more attractive • Oral contraceptives (pill) simulate hormonal effects of pregnancy • Women on hormonal birth control • find men with similar MHC more attractive • Avoid kin while sexually receptive, seek kin while pregnant (yes, new data suggests they do!)
  16. 16. Studies of Hutterite population also suggest that MHC affects mate choice • Hutterites are a small Anabaptist community in US • Marry within their community • Hutterite Marriages • mates with different MHC types more common • Mates with similar MHC types less common
  17. 17. The relationship between inbreeding avoidance (biology) and incest rules (culture) is not always clear • If aversions to inbreeding are part of human psychology, why do we need incest rules? • Why are first cousin marriages allowed in some societies, but not others?  Reflects complex interaction between biology & culture  Complex interaction between biology, psychology, & culture  True for ALL human behavior
  18. 18. Behavioral Ecology & Mate Choice: The Kipsigis • Farmers & herders in Kenya • Wealth measured as: • Amount of land owned • Number of livestock owned • Household possessions • Men marry first in late 20’s • Pay bridewealth to marry a woman • Wealthier men have more wives • Wealthier men have more kids • Women marry in late teens • Father’s arrange marriage • But daughters give consent 0 2 4 6 8 10 12 1 2 3 4 5 6 7 8 Number of Wives NumberofMen
  19. 19. What makes a desirable Kipsigis husband? • Wives are given a plot of the husband’s land • Women with larger plots • Can grow more food • Have healthier kids • Have higher reproductive success 0 10 20 30 40 50 0 100 200 300 Size of Landholdings (Acres) AcresperWife Acres per wife increases as man’s landholdings increase 0 1 2 3 4 5 6 7 8 9 0 100 200 300 400 Size of Landholdings (Acres) NumberofWives Men with more land have more wives
  20. 20. What makes a desirable Kipsigis wife? • Men have many wives • some men get none = competition for women • Bridewealth payment goes to bride’s father • father of bride & the groom negotiate bridewealth • Bridewealth = value of the marriage partner
  21. 21. What makes a desirable Kipsigis wife? • Early maturing women bring higher bridewealth 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 High Average Low Bridewealth Category Proportion Early Late
  22. 22. What makes a desirable Kipsigis wife? 0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 Cohort 1 Cohort 2 Cohort 3 LiveBirthsperYear Early Maturing (12-14) Late Maturing (16-19 • Early maturing women have higher reproductive success
  23. 23. What makes a desirable Kipsigis wife? • Plump women - with plenty of nutrition & no disease - also bring higher bridewealth
  24. 24. Evolutionary psychologists also explore factors that affect mate choice • Adapted to choose mates who enhance our reproductive success: Sex differences • Males • Increase number of matings • Prefer mates who can produce more offspring • Particularly important when pair-bonding common • Females • Get more resources to provide to offspring • Reduce mortality • Improve quality of genes in offspring (by selecting them in mate) • Don’t commit the Naturalistic Fallacy!
  25. 25. As a pair-bonding species, we also predict similarity in mating strategies & preferences • Able to produce many healthy children • Able to provide good care for children • Willing to invest in children • Not likely to be unfaithful Charles DarwinEmma Wedgewood
  26. 26. Evolutionary psychologists predict that women’s mate choice criteria will be related to resources • Human infants require extended care • In foraging societies, men contribute critical resources for women and children • Women’s fitness enhanced by male provisioning • Females will prefer mates who can and will provide resources for offspring • In societies in which individuals can acquire property and resources, females will prefer wealthy males
  27. 27. Male mate preferences are expected to be based on female fertility • Male mating success depends on reproductive success of female • Women’s reproductive potential • peaks in early adulthood • declines until menopause • Men are expected to prefer young women • Standards of beauty are correlated with youth and health • Smooth skin • Good muscle tone • Shiny hair • Men will prefer youthful mates • Men will value good looks Aishwarya Rai - Bollywood actress
  28. 28. Both males and females must be concerned about fidelity, but this may matter more to males than females • For females • If males have multiple mates, they may divert resources to other offspring • For males • If females have multiple mates, males may be providing resources for other man’s children • Expect men to value fidelity more than women Campaign for Aids prevention in Uganda: A-abstinence, B-be faithful, C-use condoms
  29. 29. Evolutionary psychologists predict that similar preferences will exist in all societies Sample mate choice criteria in 37 countries around the world Ask people to rate importance of various traits Problems with the sample 1. mainly university students 2. mainly developed, Westernized nations
  30. 30. Preference for good financial prospects 0 0.5 1 1.5 2 2.5 3 Japan Zambia Yugoslavia Australia USA MeanRating Men Women Indispensable Unimportant CSUCI
  31. 31. Preference for good looks 0 0.5 1 1.5 2 2.5 3 Bulgaria Nigeria Indonesia W Germany USA MeanRating Men Women Unimportant Indispensable CSUCI
  32. 32. Males Females 1. Good health 2. Mutual attraction and love 3. Good looks 4. Emotional stability and maturity 5. Dependable character 6. Sociability 7. Ambition and industrious 8. Good cook and house keeper 9. Education and intelligence 10. Refinement and neatness 11. Similar education 12. Good financial prospects 13. Desire for home and children 14. Chastity 15. Similar political background 16. Favorable social status 17. Similar religious background 1. Mutual attraction and love 2. Emotional stability and maturity 3. Dependable character 4. Good financial prospects 5. Education and intelligence 6. Good health 7. Ambition and industrialness 8. Desire for home and children 9. Good cook and housekeeper 10. Refinement and neatness 11. Sociability 12. Favorable social status 13. Good looks 14. Similar religious background 15. Similar education 16. Similar political background 17. Chastity
  33. 33. However, the cross-cultural data also show that men and women care most about character Trait Males Females Mutual attraction, love 1 1 Dependable 2 2 Emotionally stable, mature 3 3 Pleasing disposition 4 4 Good health 5 7 Education, intelligence 6 5 Sociable 7 6 Desire for home, children 8 8 Refinement, neatness 9 10 Good looks 10 13 Good financial prospects 13 12 Chastity 16 18 1 1 1 3 4 6 4 7 4 4 1 2 9 7 11 10 11 13 11 11 7 9 18 15 CSUCI
  34. 34. Men and women BOTH value the traits that would contribute to long-term unions • Human children require extended period of investment • women play primary role in childcare • men make big investment in children • Stable marriage/bond increases reproductive success • Stability of marriage may be enhanced • choose a loving, dependable, stable, clever, sociable partner
  35. 35. There is also considerable cross-cultural variation in preferences Preferences about chastity are most variable Preferences about financial prospects are least variable Sex differences hold across cultures
  36. 36. Conclusions • In general, BOTH men and women want: • Mutual attraction, Love • Kindness, pleasing disposition, humor • Emotional Stability, dependability • Men emphasize youth, attractiveness, chastity more • Women emphasize resources, hardworkingness, age, status more • Differences in male and female mate preferences make sense in light of sexual selection theory • While there are big cultural differences in magnitude of preferences, reversals are rare (e.g., no reversals in age preferences)
  37. 37. After a long evolutionary history…where are we as a species? • We are adapted to be flexible in our behavior • We are adapted to rely on our brains more than our bodies • We are adapted to be social and cooperative • We are adapted to be cultural • We have evolved a lot of phenotypic variability
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