Chapter 14: The Evolution of Social Behavior – Behavioral Ecology and

Sociobiology/Evolutionary Psychology

• Food and Moving onto the Savannah

• What is social behavior?– Types of social interactions

• The Conundrum of Altruism

• Kin Selection or Inclusive Fitness

• Reciprocal Altruism

Food and Moving onto the Savannah

• Tastes• Meat:

– Rich source of nutrition by weight– Few or little poisons– “Man the Hunter” (Lee and DeVore).– Geographic spread– Meat for sex: marriage

• Reciprocity: “The Sex Contract” (Helen Fisher)

– Meat for kids: family• Kin-Selection

• Meat for friends: coalitions/politics– Hunting Return Variance problem

• Risk sharing and Reciprocal Altruism

– Meat for status• Trophies and Showing off

• Other hunting adaptations– Optimal foraging strategies

• More in Chapter 15

– Vegetables don’t have minds• Cost and benefits

– Weapon use– Perhaps music?

• Plants– Largest contribution to diet– Other primates– “Women the Gatherer”– Less risky than hunting– Less travel distances– Roots (Wrangham)

• Baboons

– Sex differences in spatial abilities

• Implies a contract between men and women– Monogamy and Fatherhood (Human Universals)

• Apes to Hunters and Gatherers– Savannah are dispersed and low density– High childhood mortality– Need Father to provision and protect

• Household based economies

– Central Place Foraging pattern– Sharing between households

• Networks of households – Lineage based social groups (patrilocality)

• Which came first?

Sexual division of labor is a human parenting strategy based on reciprocity

Social Behavior

• Group living requires tradeoffs of costs and benefits

• Social interactions are behaviors that has a fitness consequences for two or more individuals (of the same species). – Excludes:

• Parenting• Mating

• In a social interaction there is an ACTOR and a RECIPIENT(S) of the action.

• An action can be said to be beneficial (+) if it increases fitness, and costly or detrimental (-) if it decreases fitness.

Types of Social Interactions

• A taxonomy of pair wise, or dyadic, social interactions based on fitness outcomes:

Type Actor Recipient

• Selfish + -• Mutualistic + +

• Altruistic - +• Spiteful - -

The Conundrum of Altruism• Selfish and mutualistic acts increase the

fitness of the actor. It is clear that these behaviors will be selected for by natural selection, because those who act selfishly or mutualisticly derive a direct/immediate benefit from their action.

• Altruism is a problem to explain because by definition it decreases the fitness of the individual performing the behavior while increasing the fitness of a competitor (the recipient) and therefore reduces the contribution of the genes that underpin that behavior to the next generation.

• Even spiteful interactions can be explained by natural selection as long at the recipient pays a greater fitness cost than the actor.

Gives a warning call (ACTS ALTRUISTICALLY)

                                            

       

Altruism and Warning Calls

Doesn’t give a call (ACT SELFISHLY)

c<br

where  

c = the fitness cost to the individual performing the behavior

b = the sum benefits to all individuals affected by the behavior

r = the average coefficient of relatedness between the actor and recipients

Kin Selection is one answer to the puzzle: Hamilton’s (1964) theory of kin selection (inclusive fitness) predicts that

altruistic behaviors will be favored by selection if the costs of performing the behavior are less than the benefits to the

receiver discounted by the coefficient of relatedness between actor and recipient.

Giving the warning call and accounting for kin selection where the cost of giving the call is .3 and the

benefit .1 to each of the others and the actor is the sister of the others (r = .5)

                                            

      

           

                      

 

c = .3b = .1 x 8 = .8r = .5

rb = .5 x .8 = .4

Give the warning call because c<rb (.3 < .4)

• Kin selection is a powerful motivation for cooperation in social interactions.

• Kinship is an important principle for the organization social structures

• In tribal and band societies kinship is the primary principle around which groups form and is primary in defining the relationships between groups

                                                               

                        

Intertribal   

Spheres of Interaction and Influence of Kin Selection

• Among the Yanomamö the value r in Hamilton’s Rule:– Is related to how large a village gets before

fissioning – Predicts who will side with whom during conflicts – Predicts who will go with whom when a village

fissions

• Kinship is likely the most important principle underlying group structures in the EEA

• What about chimp social structures? • Kinship is also used as a principal for

organizing non-kinship based organizations like religion

Reciprocal Altruism(Trivers 1971)

c < bw

c = cost to the actor

b = benefit to the recipient

w = the likelihood that the actor will receive a benefit in the future as a result of paying the cost now.

Dano (18)  Pua (8)  Kovu (11)

DominanceRank

Modomo (8)

Kula (8)     Mark (0)

(After Hall and DeVore, 1965)

Proximity to the Central Hierarchy

Baboons show signs of Reciprocal Altruism

Game Theory:

Tit for tat and the Prisoner’s Dilemma YOU

C D 

me: R = +3 me: S = -2 C = Cooperate C D = Defect you: R = +3 you: T = +5 R = Reward for mutual cooperation

T = Temptation to defect

Me S = Sucker’s payoffP = Punishment for mutual defection

me: T = +5 me: P = 0 D you: S = -2 you: P = 0  

• In a one-time game, you should defect because the average payoff is greater.

• If the game is to be repeated many times (as is the game of life), it is in both player’s long-term interest to cooperate.

• In game theory the value w is defined as the number of times the game will be played

• Tit-for-tat is an evolutionarily stable strategy, or solution, to a repeated Prisoner’s Dilemma game. The rule is: cooperate on the first play and then do what your opponent did in the last play.

• Also known as the Golden Rule• All social interactions, like games, are competitive

(winners and losers)• Assignment: go to

http://www.cquest.utoronto.ca/zoo/bio150y/pdgame/intro.html and do the tutorial on the Evolution of Cooperation.

Evolutionary Psychology is the study of Human Nature

• Species Typical Behaviors• Innate cognitive mechanisms for making

decisions concerning specific evolutionarily stable (ES) problems and motivate actions based on these decisions.  This involves: 1. Adaptations for perceiving, recognizing, and

making salient appropriate inputs to determine if a ES problem exists, and assessing the costs and benifits. 

2. Choosing between possible solutions (STRATEGIES) to problems using the gathered inputs and filling in the blanks when information is incomplete.

3. Attaching appropriate emotional states that motivate actions that lead to probable solutions to ES problems.

• The goal of this new science of the mind is to map out all of the decision-making rules that make up human nature.

• Deep-Blue and Casperoff • Human Nature must be universal with low

tolerance for variability • Shirley McLain and Sybil Theories of

Evolutionary Psychology• Focus is on the design features of

adaptations rather then on RS– Adaptive mismatch problem

Clerical Problem

Rule: If a person has a ‘D’ rating, then his/her documents must be marked with a ‘3’ 

Social contracts and the logic of detecting cheaters:The Wason Selection Task (Leda Cosmides)

D F 3 5

Bartender’s Problem

Rule: If a person is drinking a beer, then he/she must be over 21 years old’ 

Drinking a beer

Drinking a coke

25 years old

17 years old

• Both the Abstract and Social Contract problems are logically identical (P, not Q)

• Significance :– We have specialized cognitive mechanisms

(adaptations for making decisions) for policing social contracts: CHEATER DETECTION

– If you don’t pay the cost you are not entitled to the benefit (Reciprocal Altruism and Tit-for-Tat)

– The mind is modular:• Functionally specific not just capacity for reasoning• Abstract (clerical) problem not in the form of a social

contract and we don’t turn on the cheater detection module to solve it.

Human Universals

• Color Terms • Hopi time and 7 Words for Snow • Incest Avoidance

– Kabbutz – Chinese Child Brides

• Expressions of Emotions • Social Structures • Near Universals • Universals: Innate Human Nature or

Universal Experience

Human Behavioral Ecology

• Humans are rational actors who act in ways to maximize their reproductive fitness– Adaptations lead to RS– Phenotypic Gambit (Black Box)

• Optimization vs. Maximization– Long term cost and benefits – Lack: clutch size in birds– Optimal family size (child spacing) in Chapter 19

• Optimal foraging strategies– Game choice– Size of hunting parties