a behavior performed by an individual that comes at a cost
in 1964, William Hamilton developed an idea of how traits could perhaps evolve if they increased the survival of close relatives
coefficient of relatedness(r)
may be defined as the probability that homologous alleles present in individuals are identical by descent
the probability that two homologous alleles present in the same individual are identical by descent
states that an altruistic behavior will be favored by natural selection if:
Br - C > 0
rB > C
B = benefit to recipient
C = cost to individual performing the act
altruistic behaviors will evolve when benefits to the recipient are large, the costs are relatively low, and when the individuals involved are closely related
-"direct" component refers to an individuals reproduction.
-"indirect" component which represents the gain in fitness of relatives made possible by an individual's altruistic act.
indirect component of inclusive fitness
crucial parameter in the theory of kin selection
- related individuals (such as full or half-sibs) are expected to share more alleles in common than any two randomly chosen individuals from the population.
- for half-sibs, r = 1/4.
- for full-sibs, r = 1/2
- for first cousins, r = 1/8.
"helping at the nest" benefits the actor when . . .
(1) habitats are saturated with breeding pairs or (2) when suitable nest sites are limited.
social system characterized by having (1) overlapping generations (2) cooperative group care and (3) specialized reproductive and non reproductive castes (workers). mostly social insects (bees, wasps, and ants).
single gene difference in MHC is detectable, F mate w/ M who smells different, F looks for pups who smell like her.
relatives are less aggressive to each other, open program - damaged tail mother
Unusual form of sex determination where females develop from fertilized eggs and therefore diploid, but males develop from unfertilized eggs and therefore haploid. Daughters receive identical sets of genes from their fathers and have a 50% chance of sharing mother's genes with their sisters. They're more closely related to their sisters (r = .75) than their own daughters (r = .5). Their genes will increase in the population faster if they assist in the production of sisters rather than their own offspring.
3 ways haplodiploidy doesn't explain the evolution of eusociality:
1- many eusocial colonies appear to have more than one father.
- this leads to the situation in which the average r among workers is far below 3/4.
- in these cases, natural selection would strongly favor female workers reproducing for themselves rather than help rear their sisters.
2- many colonies are founded by more than one queen.
- some workers in these colonies (the daughters of unrelated queens) have an r of 0.
3- many eusocial species are not haplodiploid and not all haplodiploid species are eusocial.
- a phylogenetic analysis of the evolution of eusociality in the hymenoptera (who are all haplodiploid) shows that it evolved several times independently in just a few families.
- it is almost invariably found in groups that build complex nests and care for their larvae for extended time periods.
- this suggests substantial ecological factors in determining when eusociality will evolve that may be helped by a haplodiploid genetic predisposition.
Altruistic behavior between unrelated individuals, whereby the current altruistic individual benefits in the future when the current beneficiary reciprocates (blood sharing in vampire bats)