5. Sociality & Cooperation

Altruism puzzle

Why help others at a cost

Kin selection

Helping relatives

Hamilton’s rule

Altruism can evolve when helping relatives is genetically “worth it” despite personal costs.

Direct reciprocity

I help you, you help me

Indirect reciprocity

Reputation-based helping

Meat sharing importance

High risk, high reward, rapid decay

Foraging skill development

Long learning period requires cooperation

Human cooperation uniqueness

Scope, scale, and variation

Scope of cooperation

Helping non-kin and strangers

Scale of cooperation

Large groups and societies

Variation in cooperation

Differences across cultures

Hadza cooperation

Group norms determine behavior

Norm following

Individuals adjust to group behavior

The Gossip Hypothesis (Dunbar)

Talking about others helps track behavior, share social info, and catch free riders.

The Social Brain Hypothesis (Dunbar)

Humans evolved their large neocortices for dealing with social complexity.

Spillover Hypothesis

Cooperation in small groups spills over into large societies.