Alturistic Social Behaviors 51.5

Introduction Survival of the fittest encourages selfish behavior “Selfish” behavior – benefits individual at the expense of others Behavior that maximizes an individual’s survival and reproductive success is favored by selection, regardless of how much damage such behavior does to another individual, population or species

Alturism (This only occurs in a select number of species) Selflessness; behavior that reduces an individuals fitness while increasing fitness of another individual EXAMPES: Belding’s ground squirrel  will alert others of predator, calling attention to itself Honeybees  sterile workers labor and die for the single fertile queen Naked mole rat  non-reproductive members feed, care for, and defend reproductive kings and queens

How can altruistic behavior be explained by evolution?

Inclusive Fitness Inclusive fitness – total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables close relatives to produce offspring Inclusive fitness provides an evolutionary explanation for altruistic behavior among animal communities. It is the expansion of the concept of the fitness of a genotype to include benefits accrued to relatives of an individual since relatives share parts of their genomes. Hence an apparently altruistic act toward a relative may in fact enhance the fitness of the individual performing the act

Hamilton's Rule And Kin Selection Biologist William Hamilton: animal can increase its genetic representation in the next generation by “altruistically” helping close relatives other than its own offspring Relatives have genes in common

Hamilton's Rule And Kin Selection According to Hamilton’s rule the 3 key variables in an act of altruism are the benefit to the recipient, the cost to the altruist, and the coefficient of relatedness Benefit – (B) is the average age number of extra offspring that the beneficiary of an alturistic act produces Cost – (C) is how many fewer offspring the alturist produces Coefficient of relatedness – (r) equals the fraction of genes that are shared on average (Siblings, parents, offspring share 50%)

Hamilton's Rule And Kin Selection Natural selection favors altruism when the benefit to the recipient multiplied by the coefficient of relatedness exceeds the cost to the alturist (rB>C)  this inequality is known as Hamilton’s rule. Kin Selection - any natural selection that favors altruistic behavior by enhancing reproductive success of relatives

Parent A Parent B  1/2 (0.5) probability 1/2 (0.5) probability Fig. 51-28 Parent A Parent B  OR 1/2 (0.5) probability 1/2 (0.5) probability Sibling 1 Sibling 2

then altruism is favored. r x B > C If > , then altruism is favored.

Reciprocal Alturism Sometimes individuals help another individual who is not closely related but in expects the beneficiary to help them in the future Christine Eiserle Catherine Moresco Sarah McGowan