Reciprocal Altruism

1
Reciprocal Altruism

• Elbert Lim
• Anthro 179

2
Reciprocal Altruism

• Term was coined by Robert Trivers (1970s).
• Refers to the offering and receiving of support,
  but at a cost to reproductive fitness.
• Relatively recent field of study no real work
  done on this subject until late 1960s.

3
Origin

• Darwins theory of evolution survival of the
  reproductively fit
• How could natural selection favor the development
  of cooperative societies, when fitness is
  compromised in these societies?

4
Three Forms of Selection

• Group selection
• Kin selection
• Reciprocity selection

5
Group Selection

• Populations of species are divided into islands,
  or demes.
• Favors any gene that lowers the likelihood of
  extinction for the deme that it occurs in.
• Survival is population density-dependent must
  stay within an optimal range
• Altruism favored because it prevented explosive
  population growth
• Wynne-Edwards 1959, 1962
• Considered the weakest principle of the three
  because
• It fails to address how and why extinction occurs
  if a population lacks the appropriate regulatory
  controls.
• Pays little attention to the possibility of
  subdivision within successful populations.

6
Kin Selection

• Principle of competition among populations is
  rejected.
• Assumes that actors can effectively identify each
  other from one another.
• Success occurs if the fraction of genetic
  material preserved within a group is greater than
  the fraction of genetic material lost.
• Exchange of altruistic behavior, as a result, is
  greater between relatives than between unrelated
  individuals.
• Hamilton hypothesis in order for altruistic
  behavior to occur, the benefits, even among kin,
  must outweigh the cost (I.e. an actor is more
  willing to give up his life to save multiple
  actors over saving just one).

7
Reciprocity Selection

• Just as in kin selection, the actors involved
  must be able to identify one another.
• Most favored principle out of the three.
• Actors involved in altruistic exchange do not
  need to be related.
• Exchange is more likely to take place with actors
  exhibiting a propensity towards reciprocating
  cooperating (I.e. youd be more likely to buy a
  round for a generous friend than with the miser
  of the group).

8
Prisoners Dilemma

• Most commonly used model in studying reciprocal
  altruism.
• Prisoners Dilemma.
• Actors in this model follow the conditions of the
  reciprocity model.
• Most common strategy used in this problem is
  Tit-for-Tat.

9
Tit-for-Tat Strategy (in order of occurrence)

• Start off by cooperating, and continue to do so
  as long as the partner does.
• Defect only when the other actor defects.
• Go back to cooperating with the partner once
  cooperation is restored by the other actor.
• When mutual cooperation occurs, go back to
  cooperating with each other.
• If multiple defection occurs, start defecting as
  well.
• Other strategies included
• Defecting on the first turn to gauge whether the
  partner could be trusted.
• Continual defection against the sucker.

10
Shortcomings of the Prisoners Dilemma

• Does not take into account group formation.
• Individuals are not capable of choosing partners,
  as in real life, in this model.
• Factors involved in changing interaction
  partners, such as migration, mutation, etc. are
  not taken into consideration.
• Such shortcomings were found as recently as the
  late 1990s.
• Zeggelinks Social Evolution Model (SEM),
  published in June 2000, offers a more inclusive
  simulation to study, but results, such as
  findings for existence of an ideal population
  density, are inconclusive.