Primates

Extractive Foraging Hypothesis (Gibson)

• Animals who need to search for food need bigger brains (do task to get food) → larger home range usually means larger brain

• Omnivorous diet = complex strategies needed

  • Fruits (large home range → mind map/directions), insects (dispersed), nuts (dispersed, tools) → all of these offer more energy than for foliovores

• Memory needs to be greater

• Different ways of processing different foods needed

• Some foods may be better obtained using tools… (nut cracking, spears, etc.)

Tool Use (ecological hypothesis 2)

Correlation between the development of a larger brain in early hominids and development of tools → the complexity and sophistication of tools made as an estimate of intelligence

Social Intelligence Hypothesis

• Big group = complex social relationships (larger groups may mean larger brain size/smarter)

• Groups living in complex social relationships may present more of a challenge than the physical environment

• They must be able to remember and understand relationships and manipulate the behaviors of others in order to survive

• Offers more evolutionary pressure than environment (directly competes with social ecological model which explains primate social structures [like group size, mating systems] as adaptations to their environment)

• Neocortex size correlates significantly with group size – Dunbar

  • Social factors appear more important than ecological ones → Primate larger brain associated with relative expansion of the neocortex as group size increase

Expensive tissue hypothesis

• Using energy for large guts is exhausting (takes a lot of energy) → reduced gut size may allow for increased brain size → are they negatively correlated? If so, high quality diet would be necessary for the evolution of large brain size

  • Aiello & Wheeler found significant negative correlation between relative brain weight & relative gut weight

• Brain uses ~25% of adult metabolic energy; ~50% in young children

Theory of Mind

Gaze following

Seeing and Knowing

Intentionality

Attribution of Knowledge (false beliefs)

Contingent reciprocity versus Biological Markets

Contingent reciprocity (tit-for-tat) → random partner choice

Biological markets → partner selection (ex: grooming traded for tolerance)

Emotion-based reciprocity (bonds, attitudes)

• Ex: will they answer a distress call for nonkin? Yes, but usually only if they recently groomed them.

*reciprocal altruism requires them to not be kin (and for them to have good memory and recognize them)

Acoustic communication example