October 06, 2004

Hamilton's Rule or Why Ethnic Nepotism is not (usually) Adaptive

Continuing the previous entry on Ethnic Nepotism and Kin Selection to make the points raised there more formal. The bedrock of kin selection theory is Hamilton's rule, which states that altruistic behavior of X towards an individual Y is adaptive depending on three factors:
  • The relatedness r of X to Y
  • The cost C of the altruistic behavior (reduction in fitness of X)
  • The benefit B of the altruistic behavior (increase in fitness of Y)

Hamilton's Rule states that altruistic behavior is adaptive when the inequality rB-C>0 holds. Equivalently, an altruistic behavior is adaptive if its cost is C<rB. Since r between co-ethnics is low, most altruistic behavior towards them is non-adaptive; or as I stated informally, it is the few "dramatic actions" which are only adaptive.

Sure, it's better to do an altruistic act for a co-ethnic than a foreigner. But it's better in the sense that you lose less if you help a co-ethnic than a foreigner. Your genes don't gain anything in either case. Altruism is adaptive for your close kin. Altruism for your co-ethnics or foreigners is (usually) a strictly lose or lose-more proposition.

1 comment:

Grey said...


individual behaviour which may be maladaptative most of the time becomes critically adaptive in war, especially in eras where losing meant massacre.

this doesn't change anything from an individual selection point of view but

environment -> culture -> cultural selection pressures

cultural selection creates the pressure to promote traits that are needed in wartime.