Transcript The Evolution of Social Behavior

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
Sexual division of labor is a human
parenting strategy based on reciprocity
• 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?
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
• Altruistic
+
+
-
+
+
• Spiteful
-
-
• Selfish
• Mutualistic
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.
Altruism and Warning Calls
Gives a warning call (ACTS ALTRUISTICALLY)
Doesn’t give a call (ACT SELFISHLY)
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.
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
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 = .3
b = .1 x 8 = .8
r = .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
Spheres of Interaction and Influence of Kin Selection
Intertribal
• 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.
Baboons show signs of Reciprocal Altruism
Proximity to the Central Hierarchy
Kula
(8)
Dano
(18)
Dominance
Rank
Pua
(8)
Mark
(0)
Modomo
(8)
Kovu
(11)
(After Hall and DeVore,
1965)
Game Theory:
Tit for tat and the Prisoner’s Dilemma
YOU
C
D
me: R = +3
me: S = -2
you: R = +3
you: T = +5
C
C = Cooperate
D = Defect
R = Reward for mutual cooperation
T = Temptation to defect
S = Sucker’s payoff
P = Punishment for mutual defection
Me
me: T = +5
me: P = 0
you: S = -2
you: P = 0
D
• 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/i
ntro.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
Social contracts and the logic of detecting cheaters:
The Wason Selection Task (Leda Cosmides)
Clerical Problem
Rule: If a person has a ‘D’ rating, then his/her documents must
be marked with a ‘3’
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