Lecture 11: Summary of Readings

Cute meerkats actually vicious baby killers: Cooperative society gets stressed out when babies are involved. by Richard Van Noorden (Optional)

Dominant meerkat female chases and attacks subordinate females when she becomes pregnant, driving them away for up to 3 weeks before her own pups are born. The glucocorticoid hormones- a sign of stress - of subordinate females shoot up when under attack, reducing their chance of getting pregnant.

Advantage to Dominant female
Her pups get all the subsequent baby care to themselves.
Reduces chance of pregnant subordinate females killing her pups.

It is a clash between selfishness and cooperation.
There is a vicious power struggle between dominants and subordinates to see who manages to breed — which the dominant female usually wins. But after that, the cooperative behavior kicks in and everyone helps to rear the young.

This study is the first good evidence that a cooperatively breeding species uses aggression-induced stress to actively stop subordinate females from breeding.

Five Rules for the Evolution of Cooperation by Martin A. Nowak (Optional)

The author starts by noting the paradox that because of natural selection, one would expect that "every gene, every cell, and every organism should be designed to promote its own evolutionary success at the expense of its competitors," and yet we observe cooperation on many levels of biological organization. He uses game theory to describe five mechanisms that may explain the evolution of cooperation.

Kin Selection
In this mechanism, natural selection can favor cooperation between relatives because of shared genes. The cooperator may sacrifice so as to benefit a relative who will pass on some portion of the same genes. In mathematical terms, cooperation can evolve when the probability of sharing a gene exceeds the cost-to-benefit ratio of the altruistic act. This is known as Hamilton's rule. It is important to note that cooperation also occurs between unrelated individuals, so kin selection cannot be the only explanation for the evolution of cooperation.

Direct Reciprocity
If same individuals expect to encounter each other many times, they may cooperate in anticipation of future cooperation (this scenario is known as the repeated Prisoner's Dilemma). Computer models of repeated Prisoner's Dilemma games have shown that strategies that include elements cooperation are most successful. Specifically, tit-for-tat (which always starts with a cooperation and then does whatever the other player has done in the previous round) will enable cooperation when nearly everybody is a defector and, once cooperation is established, win-stay, lose-shift strategy (in which one repeats their previous move whenever they are doing well and changes otherwise) will serve to maintain cooperation.

Indirect Reciprocity
Because helping someone can improve one's reputation and improved reputation increases the likelihood receiving help from others, indirect reciprocity also provides a mechanism for the evolution of cooperation. Because such indirect reciprocity requires strong cogitative abilities – for tracking and communicating about one's own reputation and the reputation of others in the group – the author suggests that selection for indirect reciprocity played key roles in the evolution of human intelligence, morality, and social norms.

Network Reciprocity
Because individuals are not mixed equally and some mix more often than others, cooperators may form network clusters within which they help each other. This may enable them to prevail over defectors.

Group Selection
Selection can act on groups as well as individuals. Groups made up only of cooperators may grow faster than groups of defectors and therefore outcompete them over time.

The author goes on to show how each of these mechanisms can be illustrated with a standard 2 × 2 payoff matrix.

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