Group Selection & Altruism

9/29/08 Group Selection & Altruism Darwin's natural selection is selection of individuals, not groups Modern study of animal behavior coincides with the realization that selection acts at the level of the individual (or the gene actually) and rarely at level of larger groups (group selection) Two problems with group selection: Logical problem Generally fails to predict correctly Selection acts on individuals But many behaviors do appear to benefit group at a cost to the individuals; they are altruistic. Altruism: an individual acts to further the reproductive success of another individual(s) at some (reproductive) cost to itself. Selfish individual survives Ex: lemmings run into water ? one with intertube Ex: belding ground squirrel ? gives alarm call of predator ? one giving call is most likely to get caught b/c calling attention to self (negative effect on self but good for group) Individual and group selection arguments make different predictions as to whether these classes of animals should alarm call Class Group Indiv. Males yes no Females with pups no yes Females without pups no no/yes (depends if related) Pups no yes Group Selection: behaviors that maximize survival of groups/species are selected Individual selection: behaviors that maximize survival of the individual are selected Tinbergen?s ?4 Questions? Proximate: cause or mechanism Environmental factors inferred mechanisms genetic mechanisms neuro-physiological mechanisms Proximate ? development (history-why certain actions) Ultimate-function (how is it adaptive?) Ultimate-phylogeny (evolutionary history) Four methodological approaches to studying behavior ? and the issue of ecological validity vs. experimental control Field observation Comparative method Field experiment Lab experiment Bird Song Repertoires Why do birds have more than one song type? Females like males with numerous songs Males with bigger repertoires do better in male-male competition Beau Geste hypothesis Anti-Habituation hypothesis Advantages of matching hypothesis Males-bigger song control regions in brain = bigger song rep. Repertoire size is generically determined Males that hear songs more when growing up develop more songs later Ultimate-Function Function of song: female attraction Ex: superb lyrebird Mimic other species songs Female preference testing using copulation solicitation display (peep show) Ex: females solicit more to bigger repertoires Field experiment: nest boxes attract females more Comparative methods: repertoire size larger in monogamous species where female choice for male quality is stronger *Song repertoire=better male quality Field observation: males with larger rep. size are chosen first Weakness: separation in control of variables (could be using age, habitat, etc) Song Function Male-male competition Compete over territories Territorial context of counter-singing Song is a long distance signal Birds sing instead of fighting If they do get close, they fight Removal-keep out experiment (loud speakers play songs in certain areas) Rep. of songs more effective as keep out signal than a single song