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
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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
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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-fortat, reconciliation, etc.
• Chimp polygyny vs human pair-bonding
– Resource sharing, protection against sexual
coercion, male cooperation
Bonobo biology
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“pygmy chimpanzee”
Structural similarities to astralopithecines
Locomotion - bipedalism, knuckle-walking
Restricted range
Foraging ecology
Group size
Bonobo vs. chimp
Bonobo stature
Sociosexual behavior
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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”
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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