Week 8: Primate Social Behavior

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Week 8 Primate Social Behavior
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Sociality

• Why be social?
• Social living involves costs
• Competition for all resources
• Intra-group violence (including infanticide)
• Disease transmission
• What are the benefits?
• Two reasons (Alexander)
• To avoid predation
• Safety in numbers (tend to form large groups)
• Harder to feed everyone
• Common resources capture
• Social hunters (tend to be small)
• Diminishing return problem
• Collective defense of territory or competition
  with other groups
• Balance of power

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Types of Primate Social Groups
Solitary Orangutans
Polygyny one-male Gorillas
Monogamous Gibbons
Polygyny multimale Chimps
Polyandrous Tamarinds
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Brain to Body Weight Across Species
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Food or Social Interactions?
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Getting Enough to Eat

• Larger animals need more food overall
• Smaller animals need proportionally more calories.

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Nutrients and Toxins

• Primates have diverse diets
• Different primates eat different combinations of
  foods
• Need a good source of protein and a good source
  of carbohydrates (sugars)

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Body Size and Diet are Related
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Different Diets have Different Adaptive Problems
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Eating, Traveling Resting
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Territories vs. Ranges
Territories are not overlapping, boundaries are
defended
Ranges are overlapping, not exclusive
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Predation

• Smaller primate more likely to be victims of
  predators
• Higher predation may lead to larger primates and
  a shift in food
• Effects choice of where you live
• Different defense mechanisms
• Shelters
• Activity patterns (diurnal, nocturnal)
• Warning calls
• Form of cooperation (Kin selection/Inclusive
  Fitness
• Multi species cooperation (Reciprocal Altruism)
• Different calls for different predators

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Resource Competition and Dispersal Patterns

• Resources are patchy and limited
• Greater competition and dominance hierarchies
• Within group competition greater than between
  group
• Females will form kin based coalitions
• Females will form dominance hierarchies
• Female philopatry Matrilocal
• Between group competition gt within group
  competition
• Females will be more egalitarian
• Females will still favor kin and be philopatric

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• Both within and between group competition is
  strong
• Combination of the previous two contexts
• Females favor kin groups philopatric
• Females more egalitarian
• When resources are dispersed you get scramble
  competition
• Females have little motivation to form dominance
  hierarchies
• Females have little reason to form coalitions or
  be philopatric
• Rare?
• Where are the males?
• Males go where the unrelated females are.
• If females are philopatric then males must leave
  their natal group to avoid inbreeding depression.
• The more females in a group the more they become
  a defendable (patchy) reproductive resource for
  males
• The more females in a group the harder for one
  male to monopolize them, especially if they have
  asynchronous estrus.

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How do Chimps and Humans Fit in all of this?

• Not very well!
• Male philopatry Patrilocal (even Bonobos)
• The socioecological models presented in you book
  would lead you to believe that Chimps and our
  common ancestor live in a scramble competition
  context, but they dont, and they are
  territorial.
• Other possibilities?
• Wrangham and Madson argue that
• Chimps and Human males will be territorial if
  resources are defendable (patchy) and important
  to females
• If resources are not defendable, males will fight
  over females

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Cost of Grouping Hypothesis (Wrangham)

• Males have an advantage in the cost of grouping
• Males can forage farther for the same energy
  costs (more efficient) because they are caring
  babies or the extra weight of pregnancy (women
  paying a higher cost for reproduction)
• You can put more males in a given area (fixed
  amount of food) than you can put females
• Because of the lower cost of grouping men form
  larger groups than males.
• They use there larger coalitions to compete with
  other groups of males, but also to dominate
  females.

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What about Bonobos?

• Bonobos dont compete with gorillas for food
• More food to eat
• The cost of grouping goes down for males and
  females
• Females are not longer disadvantaged in terms of
  the cost of grouping
• Females are better at forming coalitions (through
  sex) despite male philopatry (Patrilocallity)
• Females dominate Males

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Evolution of Culture

• Culture is about learning
• Cultural behaviors that are not innate
• Acquired in a social context
• Is culture unique to humans?
• NO
• Unique to Apes?
• NO but rare
• Social facilitation vs. Observational learning
• Monkeys dont ape

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Adaptations for Observational Learning led to

• The ability of innovations to spread through a
  population without having to evolve new
  adaptations.
• Individuals not having to start from scratch,
  they could build on the knowledge and skill of
  others
• Cultural explosion
• Homo Erectus tools (choppers) were vary useful
  but did not change.
• With Modern Humans there was something equivalent
  to adaptive radiation with behaviors (tools, art,
  subsistence practices, etc.,)
• New Data indicate that Observational learning has
  special features
• Joint attention
• Functional understanding of cause and effect.