Tree of Origin

What Primate Behavior Can Tell Us About Human Social Evolution

On Becoming Human

• What are the implications for our humanity of our evolutionary origins?

• Our mental heritage

• Evolutionary origins of ethics, morality, religion

• 40 million years of primate social evolution

Comparative Studies

• Basic primate phylogeny and taxonomy

• Homologies, convergent evolution, parallel evolution

• Cultural evolution vs. biological evolution

• Tree of Origin: studies of field and captive populations of primates, by primatologists

Primate phylogeny

Hominoid taxonomy

Chapter 1

• Anne Pusey - Of Genes and Apes: Chimpanzee Social Organization and Reproduction– For many decades, chimpanzees have been observed at

Gombe National Park and other African field sites. Now DNA analyses have begun to further enrich our understanding of their social life. Chimpanzee behavior and ecology are reviewed here, along with the genetic implications for kinship, paternity, and inbreeding.

Chapter 2

• Frans de Waal - Apes from Venus: Bonobos and Human Social Evolution– Even though bonobos are as close to us as

chimpanzees, the species is less well known both to science and to the general public. These “make love, not war” primates have evolved peaceful societies with female bonding and female dominance. As such, bonobos challenge traditional assumptions about human social evolution.

Chapter 3

• Karen Strier - Beyond the Apes: Reasons to Consider the Entire Primate Order– What is special, or not so special, about the hominoids?

Comparisons between humans and the anthropoid apes are highly informative, but we cannot make sense of this small taxonomic group’s characteristics without taking a broader comparative perspective that encompasses the two hundred other extant primate species.

Chapter 4

• Craig Stanford - The Ape’s Gift: Meat-eating, Meat-sharing, and Human Evolution– Meat is highly prized by both humans and

chimpanzees. Data on cooperative hunting by male chimpanzees allow us to revisit the old Man-the-Hunter debate, initiated when only humans were thought to be carnivorous. As a part of political and mating strategies, hunting may have driven the evolution of social intelligence.

Chapter 5

• Richard Wrangham - Out of the Pan, Into the fire: How our Ancestors’ Evolution Depended on What They Ate– What allowed the descendents of chimpanzee-like

ancestors, 5 million to 6 million years ago, to colonize savanna woodlands? They appear to have depended on eating roots. About 4 million years later, our ancestors became human. A new hypothesis suggests that this happened as a result of the adoption of cooking.

Chapter 6

• Richard Byrne - Social and Technical Forms of Primate Intelligence– Can we reconstruct the “ancient mind” by speculating

about the capacities upon which our ancestors’ cognitive evolution was founded? Was it in the social domain that things began - with deception and perspective-taking; in the technical domain - with tool use; or in the context of foraging and complex food manipulation?

Chapter 7

• Robin Dunbar - Brains on Two Legs: Groups Size and the Evolution of Intelligence– Group size is a likely measure of social complexity,

which in turn may have driven the evolution of intelligence. There is indeed evidence that primates who live in large groups have larger brains. The subsequent evolution of language further promoted effective information exchange and social integration.

Chapter 8

• Charles Snowdon - From Primate Communication to Human Language– Does animal vocal communication - from the babbling

of marmosets to the song-learning of birds - provide clues about language origins? Since many features of human language are present in the communication of other species, meaningful parellels can be drawn. No nonhuman animal shows all of the human features, however.

Chapter 9

• William McGrew - The Nature of Culture: Prospects and Pitfalls of Cultural Primatology– If other primates transfer skills and habits from one

generation to the next, are we not fustified in speaking of culture as well? Wild chimpanzee communities, for example, vary greatly in tool use and special forms of communication. This intergroup diversity suggests that we are not the only cultural beings.

Chimpanzee social groups

• Small temporary parties - communities

• Fusion-fission structure of populations

• Female sexual status and groups

• Males group more frequently, wider ranges

• Foraging ecology and groups

Female ranges

Group territoriality

• Groups (communities) in defined ranges

• Intergroup aggression at boundaries, against stranger females as well as males

• Aggressive displacement/elimination of groups by others

Mating patterns

• Females advertise receptiveness• Extreme polygyny - infanticide avoidance

– Male options: opportunistic mating, aggressive guarding, consortships

– Sexual dimorphism

• Male philopatry - female-biased dispersal– Inbreeding avoidance

• Male coalitions and dominance structures

Female advertisement

Chimp hunting & meat sharing

• Prey on a variety of mammals (colobus)

• Hunting is seasonal, related to group size

• Hunting vs. scavenging

• Nutritional vs. social aspects of meat– Other foods more profitable– Use of meat in coalitions, courtship

• “Man-the-Hunter” model

Chimpanzee “model”

• Male and female social strategies

• Intergroup aggression in chimps and human societies - killer ape myth

• Chimp politics and social relations - tit-for-tat, reconciliation, etc.

• Chimp polygyny vs human pair-bonding– Resource sharing, protection against sexual

coercion, male cooperation

Bonobo biology

• “pygmy chimpanzee”

• Structural similarities to astralopithecines

• Locomotion - bipedalism, knuckle-walking

• Restricted range

• Foraging ecology

• Group size

Bonobo vs. chimp

Bonobo stature

Sociosexual behavior

• Extensive non-reproductive sex

• Reconciliation from aggression

• Food sharing

• Extended receptivity and advertisement by females

Genito-genital rubbing

Mating patterns & sociality

• Female-biased dispersal and male philopatry

• Socio-sexual behavior and female dispersal– Secondary sisterhood

• Female coalitions and dominance

• Male maternal bonding

• Low confidence of paternity

Bonobo “model”

• Food resources and group size

• Female receptivity -> less male competition

• Reduced male coalitions

• Female collective power takeover

• Sociosexual bonding among females

• Confused paternity -> no infanticide

• Low intergroup aggression

Phylogeny, ecology, sociality