# Essay on Selfish or Selfless - 863 Words - StudyMode

From these expressions for the fitnesses of the two types of organism,we can immediately deduce that the altruistic type will only befavoured by selection if there is a statistical correlation betweenpartners, i.e., if altruists have greater than random chance of beingpaired with other altruists, and similarly for selfish types. Forsuppose there is no such correlation—as would be the case if thepairs were formed by random sampling from the population. Then, theprobability of having a selfish partner would be the same forboth *S* and *A* types, i.e., P(*S*partner/*S*) = P(*S* partner/*A*). Similarly,P(*A* partner/*S*) = P(*A*partner/*A*). From these probabilistic equalities, it followsimmediately that *W*(*S*) is greaterthan *W*(*A*), as can be seen from the expressions for*W*(*S*) and *W*(*A*) above; so theselfish type will be favoured by natural selection, and will increasein frequency every generation until all the altruists are eliminatedfrom the population. Therefore, in the absence of correlation betweenpartners, selfishness must win out (cf. Skyrms 1996). This confirms the point noted insection 2—that altruism can only evolve if there is a statisticaltendency for the beneficiaries of altruistic actions to be altruiststhemselves.

## Selfish or Selfless On March 13, ..

### Prosocial Behavior | Learning to Give

The question we are interested in is: which type will be favoured byselection? To make the analysis tractable, we make two simplifyingassumptions: that reproduction is asexual, and that type is perfectlyinherited, i.e., selfish (altruistic) organisms give rise to selfish(altruistic) offspring. Modulo these assumptions, the evolutionarydynamics can be determined very easily, simply by seeing whetherthe *S* or the *A* type has higher fitness, in theoverall population. The fitness of the *S*type, *W*(*S*), is the weighted average of the payoff toan *S* when partnered with an *S* and the payoff toan *S* when partnered with an *A*, where the weights aredetermined by the probability of having the partner inquestion. Therefore,

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This simple model also highlights the point made previously, thatdonor-recipient correlation, rather than genetic relatedness, is thekey to the evolution of altruism. What is needed for altruism toevolve, in the model above, is for the probability of having a partnerof the same type as oneself to be sufficiently larger than theprobability of having a partner of opposite type; this ensures thatthe recipients of altruism have a greater than random chance of beingfellow altruists, i.e., donor-recipient correlation. Whether thiscorrelation arises because partners tend to be relatives, or becausealtruists are able to seek out other altruists and choose them aspartners, or for some other reason, makes no difference to theevolutionary dynamics, at least in this simple example.