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The Survival of Altruism

Picture this: You’re in the jungle, out helping to gather food for your tribe, when you see a predator stalking towards camp. You can a) scream a warning to your tribe, letting the predator know exactly where you are, or b) stay silent and let the tribe get attacked, saving yourself. Your choice depends largely on what this article defines as an “altruism gene”.

According to Darwin, it seems like anyone altruistic enough to choose (a) will end up as a tribe sacrifice, while all those selfishly choosing (b) will live to spread their selfishness into the next generation. Yet we still run in to overly charitable people today, and there are constant reports of Vervet monkeys warning their groups of an attack even at cost to themselves.

So how does altruism survive in a society? One theory mentioned by the article is that the beneficiaries of altruism are more likely to be altruists themselves. This can be set up as a Prisoner’s Dilemma with two different types of society members, Altruist (A) and Selfish(S). The “payoffs” in this case are in units of reproductive fitness, or how easily the player’s particular type of altruism gene A or S will be able to pass to the next generation.

                                   Player 2
                            Altruist         Selfish
Player 1   Altruist       11,11            0,20
               Selfish         20,0             5,5

The article attempts to determine through this matrix which type will be favored through natural selection. To simplify the scenario, it is assumed that reproduction is asexual (i.e. finding a mate is not an issue), and that altruistic parents have altruistic children. Likewise, selfish parents would only have selfish children. To find the weighted average of reproductive fitness, the probability of having a selfish or altruistic partner is measured, given the player is one or the other themselves. So for an altruistic person the equation is:

W(A) = 0 * Prob(S partner/A) + 11 * Prob(A partner/A)

While for a selfish person it is:

W(S) = 5 * Prob(S partner/S) + 20 * Prob(A partner/S)

From these equations it becomes clear that if it is equally likely that the partner may be altruistic as selfish, then altruism would have died out long ago. However, if it is more likely that altruistic players “play” against other altruists, thereby leaving selfish players to play themselves, then W(A)>W(S). Since the beneficiaries of the altruistic players come from the same drawing pool of the “other players” they face, the existence of altruism at all lends credit to the theory that those who benefit from altruism are altruistic themselves. Essentially, the altruistic create a network amongst themselves, so that they help each other survive and give the altruism gene to the next generation.

Which is the sort of answer you would expect from altruistic people, really.


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