Becoming Human: Evolution of pair-bonding Social systems of our primate relatives: 1.Old world monkeys: Female bonded groups 2.Gibbons: monogamy 3.Orangutans:

Becoming Human: Evolution of pair-bonding

Social systems of our primate relatives:1. Old world monkeys:

Female bonded groups2. Gibbons: monogamy3. Orangutans: exploded

harems4. Gorillas: true harems5. Chimpanzees,

bonobos: multi-male/female groups, male-bonded groups

Early hominins

A. ramidus (Ardi) low sexual dimorphism 5-4.4 mybp;A. afarensis (Lucy) 3.3 mybp high sexual dimorphismAustralopiths are generally assumed to have had high male-male competition;

harems, single male – female bonded groups

Homo erectus: grade shift

• Increasingly dependent offspring• Lower sexual dimorphism (increase in

female body size especially)• Larger, more cooperative social groups• Evolutionary dilemma – creating

cooperative muliti-male/female breeding groups with high paternal investment (which requires paternal certainty)

• Canine model? High pa, but exclusive breeding

• Primate model? Multiple breeding, but low pa

Sexual selection: Hand axes over brawn?

Hand axe as sign of male quality?Symmetry; appreciation of beauty;

resourcefulness; artistic skill? Unused hand axes – practice; display?Male domestication?Beginning of the “meat for sex” deal?Cooperative hunting among Homo

heidelbergensisFirst spears 400,000 ybp (Schoningen, Germany)

Neanderthals: Sexual division of labor?

Some archaeological evidence suggests less sexual division of labor among Neanderthals (lack of ‘tailoring’ artifacts; robustness of female bodies).

Less division – more ‘fragile’ social system?

Clear division of labor in traditional human societies.

Sex role specialization

• Kuhn & Stiner (2006): Neanderthal remains provide no evidence of

“women’s work.” • Neanderthal diet almost exclusively big game, no significant small game or

vegetable matter• No evidence of bone needles or awls indicating tailored clothing

“No matter how one chooses to interpret the ethnographicrecord, it is impossible to argue that Neandertal females andjuveniles were fulfilling the same roles … as females and juveniles inrecent hunter-gatherer groups” (Kuhn & Stiner, 2006, p. 958).

©John Wiley & Sons, Inc. 2007 Huffman: Psychology in Action (8e)

Evolution of Human Mate Attraction• Using an evolutionary approach to explain why we are

attracted to certain traits in members of the opposite sex.

• Operates at level of “gut” attractions, not conscious evaluation

• Advantages of being male:– Cheap sperm: relatively low parental investment costDisadvantage:

low paternity certaintyAdvantage of being female:

High maternity certaintyDisadvantage:

costly eggs: relatively high parental investment


David Buss: Global study on mate attractionOver 10,000 subjects from over 30 countries across the globe.

• Female attractions: decrease parental investment by getting good genes and copious resources

• Male long-term mate attractions: increase paternity certainty, while maximizing reproductive output

• Both temporarily “blinded” by romantic love


Evolved Male Attractions: Long-term mates – desire for youth


Evolved Male Attractions: Beauty


Evolved Male Attractions: Chastity


Evolved Male Attractions: Long-term mates Summary

• 1. Youth/Beauty: increase reproductive value in single mate• 2. Chastity/youth: increasing paternity certainty in offspring to

be resourced• Other relevant tendencies in males:– Madonna/Whore dichotomy– Sexual Jealousy module (sexual infidelity more arousing

than emotional infidelity)– “mid-life” crises


Evolved female attractions: Long-term matesAge


Evolved female attractions: long-term mates Financial Prospects


Evolved Female attractions: Long-term matesGood genes


Evolved Female attractions: Long-term matesGood genes


Female evolved attractions: summary

• 1. Older mate/good financial prospects: status, stability, resources

• 2. Cues of masculinity: good genes• 3. interaction with ovulatory cycle: evidence

for cuckoldry strategy?


Human mate attraction: Long term mates

• Males: young, beautiful, sexually modest

• Reproductive value; paternity certainty

• Females: older, high-status (or potential), robust

• Good genetics, stable secure source of resources.


Cross-cultural signally

Sexual Economics: Sex if the price is right for women (not men)

• Parental investment theory: Sex for women should be viewed as rare and valuable with important benefits (resources, long-term commitment, etc.). Not so for men (less investing sex).

• Females, not males, generally react negatively to explicit sexual images (cheapens sex).

• But female reactions to explicit sexual images are more positive if paired with expensive, rather than cheap product

Sex differences in Jealousy• Hypothesis: If a major concern of males is paternity certainty and major

concern of females is securing resources, then emotions may have evolved to protect this interests. Males more jealous of sexual infidelity; female more jealous of emotional infidelity

Please think of a serious committed romantic relationship thatyou have had in the past, that you currently have, or that youwould like to have. Imagine that you discover that the personwith whom you've been seriously involved became interestedin someone else. What would distress or upset you more(please circle only one):(A) Imagining your partner forming a deep emotionalattachment to that person.(B) Imagining your partner enjoying passionate sexualintercourse with that other person. (p. 252)

Controversy over forced choice method; stronger effects for males than femalesRecent review (Saragin et al, 2012) supports theory, but more needed on actual infidelity

Promiscuous vs. committed mating strategies: Shaping the social context

• More religious/politically conservative = greater opposition to recreational drugs

• More secular/politically liberal = acceptance of recreational drugs• Why does anyone care about others use of recreational drugs?• Ans: drugs connected to promiscuity; promiscuity connected to mating

strategy• Committed mating strategy threatened by promiscuity; philandering mating

strategy aided by promiscuity


Darwinian strategy to happy marriage

• For females: Men want paternity certainty, so avoid all jealousy-arousing behavior (don’t even look at other men). Also, take good care of his genes (offspring).

• For males: Women want resources. All the money is hers. Avoid spending money in any way she dislikes.

• For both: Both want health (good genes, fertility, etc.) Take care of yourselves. Have some kids – lower divorce rate among couples with kids.

Documents

Becoming Human: Evolution of pair-bonding Social systems of our primate relatives: 1.Old world monkeys: Female bonded groups 2.Gibbons: monogamy 3.Orangutans: