Becoming Human: Evolution of pair-bonding Social systems of our primate relatives: 1.Old world monkeys: Female bonded groups 2.Gibbons: monogamy 3.Orangutans: exploded harems 4.Gorillas: true harems 5.Chimpanzees, bonobos: multi- male/female groups, male-bonded groups

Early hominins A. ramidus (Ardi) low sexual dimorphism mybp; A. afarensis (Lucy) 3.3 mybp high sexual dimorphism Australopiths 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 heidelbergensis First 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 ethnographic record, it is impossible to argue that Neandertal females and juveniles were fulfilling the same roles … as females and juveniles in recent hunter-gatherer groups” (Kuhn & Stiner, 2006, p. 958).

©John Wiley & Sons, Inc 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 cost Disadvantage: low paternity certainty Advantage of being female: High maternity certainty Disadvantage: costly eggs: relatively high parental investment

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) David Buss: Global study on mate attraction Over 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

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved Male Attractions: Long-term mates – desire for youth

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved Male Attractions: Beauty

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved Male Attractions: Chastity

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

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved female attractions: Long-term mates Age

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved female attractions: long-term mates Financial Prospects

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved Female attractions: Long-term mates Good genes

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) Evolved Female attractions: Long-term mates Good genes

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

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

©John Wiley & Sons, Inc Huffman: Psychology in Action (8e) 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 that you have had in the past, that you currently have, or that you would like to have. Imagine that you discover that the person with whom you've been seriously involved became interested in someone else. What would distress or upset you more (please circle only one): (A) Imagining your partner forming a deep emotional attachment to that person. (B) Imagining your partner enjoying passionate sexual intercourse with that other person. (p. 252) Controversy over forced choice method; stronger effects for males than females Recent review (Saragin et al, 2012) supports theory, but more needed on actual infidelity

Romantic Love Buss: love “blinds” so as to facilitate pair-bonding. Recent evidence suggests adaptive function Evidence: – Universality – Distinctive ns signature (brain reward system, ventral tagmental area (VTM), similar to addiction) – Mate pursuit suppression – Positive effects on well-being both of lovers and offspring But what about…? Divorce – rate is lower than most people think (37% for first time marriages, 17% over first 5 years Arranged marriages – input of participants usually present; preferences of parents usually similar to their children Infidelity – rates lower than you think and lower than most other pair-bonded mammals Polygamy – real practice is far lower than what is permitted, pair-bonding problems nearly always present

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

Mate Ejection Module? Adaptive function of breaking up – getting rid a mate who compromises fitness – Males: cut loses in questionable paternity circumstances – Females: save time in questionable investing circumstances Evidence: Males more aroused by sexual infidelity; females by emotional Primary vs. Secondary ejection (getting rid of vs. moving on) Genetic contribution to divorce (30-40% of variability heritable) Divorce rate higher among non-breeders (ejection for non-fertility?)

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