CHIMPANZEE WARFARE  First documented Gombe National Park in January, 1974  Eight males formed a fighting party  Crossed border of their usual range  Attacked isolated male for 10 minutes as a group  Individual assumed to have died  First time coalition observed raiding neighboring territory and resulting in lethal attack on member of their own species

HUMANS AND CHIMPANZEES  Unique pattern of aggression shared with no other known species  Caused some rethinking of warfare as solely a cultural or social process  With regularity coalitions voluntarily choose to initiate coalitional aggression  Tooby and Cosmides explored evolutionary aspects in frequently cited article

CONTEXT OF THEORY  Darwin proposed warfare influenced human brain evolution  Group selection proposed by Alexander (larger group gains resources)  Individual/genic selection argued by Durham (survival and reproduction improved inclusive fitness) ; theory was criticized for lacking economic motives, not answering rarity of warfare or male predominance  Tooby and Cosmides answered with the theory we read

INDIVIDUAL AGGRESSION VS. COALITIONAL AGGRESSION  Large gap between group level behavior and individual adaptation  How does group aggression function adaptively?  How is group aggression consistent with individual selectional thinking?

INDIVIDUAL AGGRESSION COALITIONAL AGGRESSION ~Fight ~War  Gain resources/promote fitness  All species  Common  No cooperation  Gain resources/promote fitness  Chimps and humans as killers  Rare  Cooperation

SURPRISING FEATURE OF WAR IS COOPERATION

ANALYSIS OF COOPERATION EXPLAINS…  Adaptive obstacles  Rarity among animals  Appeal of war

ADAPTIVE OBSTACLES “It is difficult to see why any sane organism, selected to survive and genetically propagate, should seek so actively to create conditions of such remarkable personal cost and danger” ~Tooby and Cosmides

RARITY AMONG ANIMALS  Coalitional aggression evolved because it promoted fitness  Why is coalitional aggression not MORE common?  Elephant seals/Hanuman langurs don’t use coalitional aggression

APPEAL OF WAR  Males seem less concerned about individual somatic welfare than females  Universal in humans, prized and glorified

Evolution of Cooperation and Coalitional Aggression Advances in evolutionary biology and game theory show that cooperation can exist if:  There is ecological stability for enhanced payoffs  Individuals can discern cooperators from non- cooperators  Individuals can exclude cheaters from the group benefit (Axelrod, Hamilton, Trivers, Smith)

Modern Simulations Ask…  Are gains from trade available?  What is the amount of repeat interaction?  What is the availability of information about others behavior? These criteria provide an Evolutionary Stable Strategy (ESS) for cooperative interaction within a group environment

Cooperation depends on sophisticated cognition  The phylogenetic distribution of sophistically advanced species is rare  Such specialized information processing cannot be culturally learned, or be a product of general intelligence  Must be adaptively designed systems specialized for these functions (Darwinian Algorithms)

MULTI-INDIVIDUAL COMPLEXITY  With more than two individuals the cognitive problem becomes more complex  Must track performance and levels of participation  Modifying individual behavior for acceptance by group (Consensus)

Evolution of specialized cognitive mechanisms to regulate coalitional participation  Direct product of evolution  Generates behavior for the formation of coalitions, maintenance of organization, and war  Must understand the evolutionary game theoretic structure of multi-individual cooperation, and the cognitive mechanisms that produce solutions to these game theoretic preconditions  Must examine the problem at both of these levels simultaneously for a coherent exploration

“Evolutionary considerations indicate that for recurrent, evolutionarily important situations, the psyche will evolve specialized information processing procedures, Darwinian Algorithms, which can handle these situations with special efficiency. These programs should organize information into adaptively meaningful units, focus attention on adaptively important environmental circumstances, call up special inference networks, and so on, allowing the animal to solve such recurrent problems using procedural knowledge built up over thousands of generations” ~Cosmides and Tooby

TASK ANALYSIS OF SUCH PROGRAMS  Decisions regulating coalitional formation  Participation  Cost and benefit allocation

SELECTION FAVORS PARTICIPATION  Psych mechanisms regulating individual participation  Evolution of adaptations for coalitional aggression require four essential conditions

RISK CONTRACT FOR WAR  Increase in sexual access to females outweigh losses due to death  Certainty of victory  Fair allocation of benefits  Veil of ignorance about who will live or die

NO DECREASE IN AVERAGE REPRODUCTION OF MALE MEMBERS OF COALITION  With polygyny, access to females can be limiting factor for male reproduction  Female capacity doesn’t go unused due to male mortality  Each individual who dies loses, but each survivor gains to same extent  Death of males will not decrease average reproduction of the members of the coalition

FEMALES ARE DIFFERENT  Net reproduction drop is in direct proportion to females killed  Females much less likely to participate

CERTAINTY OF VICTORY  Larger group attacking smaller  Perceive so many on your side guarantees invincibility  In chimpanzees, always larger group attacking smaller or individual  Optimum level of participation sensitive to probability of success

DON’T KNOW IN ADVANCE WHO WILL DIE  Random distribution of risk of death  Death cannot seem certain or people will defect

FAIR ALLOCATION OF BENEFITS  Get more the more you put in  Raises issues of enforcement and cheaters

PROBLEMS OF ENFORCEMENT  For coalitions to stably evolve and function, the risk contract must be enforced by some or all of its members  Whom is contributing and sharing cost?  Some members of the group must exclude cheaters from sharing in the benefits, or eliminating benefits  Excluding members from group participation may be costly to the group  Forced inclusion, punishment, retaliation for nonparticipation, favored in intense coalitional participation  Active recruitment and enforcement of coalitional participation  If enforcers gain at the expense of members, than such behavior will be selected against  Mob activity seems motivated by fear of nonparticipation as well as attraction to the coalitional goal

EVOLUTION OF ENFORCEMENT  Benefits of coalitional action are not inherently a public good  Vary depending on life history variable, kin factors, and other social variables  Some may have more at stake than others  Their costs will be offset by greater marginal returns (individual benefit)

“the leader of the largest descent group is invariably the headman of the village”….”the leaders are the very individuals who decide whether killings are revenged” ~Chagnon 1988

EVOLUTION OF ENFORCEMENT  Contingent threat: “obey me or else…”  Low cost and reusable if no one “takes him up on it”  A person with a one bullet gun maintains a credible threat, so long as he doesn’t demand too much of the players  If their benefit from participation diminishes due to asymmetric group contributions, than they will revolt…”the natives are getting restless”

EVOLUTION OF ENFORCEMENT  Individuals with strongest incentives to enforce coalitional behavior will recruit additional members  By threat or exertion of pressure to actively enforce coalitional norms  Getting someone else to do the dirty work

Cosmides and Tooby argue: These and other potential solutions to the problem of enforcement, when combined with plausible assumptions about Pleistocene conditions, strong selection would have existed for the growth of an adaptively designed coalitional psychology, in a manner not requiring recourse to either group selection, cultural processes, or gene-culture evolution

Importance of exploring the evolutionary dynamics and cognitive foundations of coalitional aggression  Political complexity of post-Neolithic state systems cannot be directly reduced to models based on interband conflict in the distant past  Wars occur that few people want, fueled by political systems based on coercion of the unwilling  Modern group, political, religious, and mob phenomena

CRITICISMS  If mortality are too high, it decreases the size of your coalition, then vulnerable to victimization.  Low (1990) questioned whether theory answers why chimpanzees and human are unique?  Shaw and Wong (1989) argued that propensity for warfare equally prevalent in women and men, women playing a supportive and defense of offspring role.