1. Evolution and Kinship ANTH 321: Kinship and Social Organization Kimberly Porter Martin, Ph.D.

2. Two Approaches to the Evolution of Kinship  1. The Study of Our Primate Relatives.  2. Evolutionary Psychology

3. Our Primate Relatives  Prosimians (Lemurs, Lorises, Galagos)  Monkeys (Baboons, Tamarins)  Apes  Gibbons and Siamangs (Lesser Apes)  Orangutans  Gorillas  Chimpanzees  Common Chimps  Bonobo Chimps

4. Prosimians Lemur – multimale and multifemale groups Galago – solitary and promiscuous Loris- monogamous when associate with another animal

5. Primate Characteristics  Binocular, stereoscopic vision.  Opposable thumb/toe  Grasping hand/foot  Flat nails rather than claws  Prolongation of gestation  Prolongation of infancy and childhood  Enlarged and elaborated brain

6. Monkeys: Old World and New World Baboon – Polygynous – one male controls multiple females who mate exclusively with him Tamarin – Polyandrous – one female mates with multiple males who all stay and care for young.

7. Gibbons and Siamangs Monogamous for life – territorial and drive our same sex offspring at adolescence.

8. Orangutans Solitary in the wild except for mother infant/child pairs.

9. Gorilla 98% Identical to Humans Genetically Male-Centered groups – polygynous – with dominant males having mating priority in groups and competition between males for mating.

10. Chimpanzees 98.6% Identical Genetically to Humans www.slwaldron.com/BonoboGallery/ Bonobo Common Chimp

11. Chimps 98.6% Identical to Humans Genetically  Common Chimps  Male-centered groups  Females leave natal group at adolescence to join another group  Males stay in the same group for life  Bonobos  Female-centered groups  Males leave natal group at adolescence to join another group  Females stay in the same group for life  WHY THE DIFFERENCE?????

12. Chimp/Bonobo Differences HYPOTHESIS  One uniform species of chimp lived in the same regions as gorillas, who dominated resources located on land, relegating chimps to the resources in the trees.  Drought separated the region into two areas.  Gorillas became extinct in one area; both gorillas and chimps survived in the other area.  In the area where both chimps and gorillas survived, the patterns of ground and tree resource use continued and chimps retained male dominance as a major organizing principle. Feeding for chimps took place in the trees, making alliances between females difficult and reinforcing male dominance.  Without competition for resources on the ground, chimps were free to utilize these resources and spent great amounts of time on the ground. This allowed females to unite against males, making them equal to or dominant over them.  Bonobos time on the ground meant that they spent more time bipedally.

13. Evolutionary Psychology

14. Sociobiology Evolutionary Psychology Biologists Primatologists Ethologists Anthropologists Psychologists Linguists Lots of Controversy Fear of Social Darwinism Arguments about human free will Arguments about whether humans have instinctive (genetically programmed behavioral tendencies) First attempts to apply the theories to humans Edward O. Wilson Sociobiology: The New Synthesis 1975

15. Some Types of Evolutionary Psychology Theory Systems Theory Kin Selection/Inclusive Fitness Theory Parental Investment Theory Altruism Theory Sociability Theory Multilevel Evolutionary Theory

16. Kin Diagram Basics = male female marriage siblings = offspring

17. Kin Selection/Inclusive Fitness  Individuals will tend to invest in others in proportion to their degree of relatedness.  Degree of relatedness is calculated using the proportion of genes shared in common.

18. Kin Selection/Inclusive Fitness Theory = = === 1/2 == Cousins Brother EGO Sister Cousins 1/2 FaSi FaBr Father Mother MoSi MoBr Parent-Child ½ Grandparent-Grandchild ¼ (½ x ½) Aunt/Uncle-Niece/Nephew ¼ (½ x ½) Cousin-Cousin 1/8 (½ x ½ x ½)

19. Males Females Parental Investment Theory Relative Contributions of Males and Females to Offspring Gamete size and contribution to embryo Minimum time investment to birth of a child Minimum emotional investment to autonomous healthy child Minimum economic investment to autonomous healthy child 1/200,000 of an egg A few minutes None 200,000 times larger Nine months 5 to 7 years

20. Parental Investment Theory Male vs. Female Mating Strategies What characteristics are most sexy? Males Females Youth, Beauty Power, Wealth Very important. The female needs help with the large time, emotional and economic investments she must make to produce a healthy adult offspring. She would like her mate to stick around and help. It varies. Commitment to a single female is one of many strategies for a male. The male can offer fidelity to a single female to help support their offspring. This is only one of the male options. At the other end of the spectrum is “free copulation” leaving females to care for offspring. How important is exclusivity and commitment ?

21. Parental Investment Theory Hypotheses about The Range of Male Strategies The Swinger: Males who attract lots of females who are willing to have sex with them are better off not making a commitment to a single female. They will hope that some of the women with whom they copulate will get pregnant, and that the women will find a way to support/raise the child, either alone, or with the help of another male. This way they have the potential for having large numbers of children in whom they will have invested very little. The Nerd: Males who do not attract lots of females who are willing to have sex with them can offer commitment as an inducement for sex. They promise long term fidelity and support for the female and her offspring, allowing the female to have more children, or to raise more successful children because she has the time, emotional and economic investments of a male on whom she can count.

22. Parental Investment Theory Hypotheses about Female Strategies Females will be attracted to wealthy, powerful males who can help them support and raise their children. This will be especially true in cultures where males control resources. They may tolerate such men having multiple wives or partners as long as they and their children are supported. Females will be less exclusively monogamous when they have access to economic resources or earning power themselves. However, they will never be as promiscuous as the most promiscuous males. The risk of pregnancy and the investment that follows conception for women will make them more careful about sexual partners, and more interested in commitment from partners than will ever be true for males.

23. Hypotheses about the Evolution of Human Mating Patterns  Upright, bipedal anatomy  Enlarged brain size  Birth earlier in the developmental cycle  More helpless infants  Prolonged period of dependence  Hidden ovulation in human females  Enlarged breasts, lip size and color  Pair bonding  THE FIVE YEAR ITCH!!!