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Evolution and Kinshi p. ANTH 321: Kinship and Social Organization Kimberly Porter Martin, Ph.D. Two Approaches to the Evolution of Kinship. 1. The Study of Our P rimate R elatives. 2. Evolutionary Psychology. Our Primate Relatives. Prosimians (Lemurs, Lorises , Galagos )

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evolution and kinshi p

Evolution and Kinship

ANTH 321: Kinship and Social Organization

Kimberly Porter Martin, Ph.D.

two approaches to the evolution of kinship
Two Approaches to the Evolution of Kinship
  • 1. The Study of Our Primate Relatives.
  • 2. Evolutionary Psychology
our primate relatives
Our Primate Relatives
  • Prosimians (Lemurs, Lorises, Galagos)
  • Monkeys (Baboons, Tamarins)
  • Apes
    • Gibbons and Siamangs (Lesser Apes)
    • Orangutans
    • Gorillas
    • Chimpanzees
      • Common Chimps
      • Bonobo Chimps

Galago – solitary and promiscuous

Lemur – multimale and multifemale groups

Loris- monogamous when associate with another animal

primate characteristics
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
monkeys old world and new world
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.

gibbons and siamangs
Gibbons and Siamangs

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


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

gorilla 98 identical to humans genetically
Gorilla98% Identical to Humans Genetically

Male-Centered groups – polygynous – with dominant males having mating priority in groups and

competition between males for mating.

chimpanzees 98 6 identical genetically to humans
Chimpanzees98.6% Identical Genetically to Humans



Common Chimp

chimps 98 6 identical to humans genetically
Chimps98.6% 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
chimp bonobo differences hypothesis
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.


Edward O. Wilson

Sociobiology: The New Synthesis

Evolutionary Psychology


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








Some Types of

Evolutionary Psychology Theory

Kin Selection/Inclusive Fitness Theory

Parental Investment Theory

Altruism Theory

Sociability Theory

Multilevel Evolutionary Theory

Systems Theory

kin diagram basics
Kin Diagram Basics








kin selection inclusive fitness
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.

Kin Selection/Inclusive Fitness Theory











FaSi FaBr Father Mother MoSi MoBr






Cousins Brother EGO Sister Cousins

Parent-Child ½

Grandparent-Grandchild ¼ (½ x ½)

Aunt/Uncle-Niece/Nephew ¼(½ x ½)

Cousin-Cousin 1/8 (½ x ½x ½)

parental investment theory relative contributions of males and females to offspring
MalesFemalesParental Investment TheoryRelative Contributions of Males and Females to Offspring

200,000 times larger

Nine months

5 to 7 years

5 to 7 years

1/200,000 of

an egg

A few minutes



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

parental investment theory male vs female mating strategies
Parental Investment TheoryMale vs. Female Mating Strategies



Power, Wealth

Youth, Beauty

What characteristics are most sexy?

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.

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.

How important is exclusivity and commitment?

parental investment theory hypotheses about the range of male strategies
Parental Investment TheoryHypotheses aboutThe Range of Male Strategies

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.

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.

parental investment theory hypotheses about female strategies
Parental Investment TheoryHypotheses aboutFemale Strategies

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.

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.

hypotheses about the evolution of human mating patterns
Hypotheses about the Evolution ofHuman 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