altruism presented a “special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory.”
Darwin 1859
Reciprocal altruism can evolve only under a restricted set of conditions
A will help B, if B will help A in the future
Need:-repeated interactions
-individual recognition
Reciprocal altruism
grooming
Vampire bats reciprocate by sharing blood meals.
They usually share with close relatives or non-relatives who are roostmates and may later reciprocate
Reciprocal altruism
Most alleles favored by kin selection rise to high frequency by inducing altruism toward individuals likely to be carrying copies of the same allele
Selection can favor making sacrifices for kin; it should also favor avoiding sacrifices for non-kin
Kin selection
Inclusive fitness consists of direct fitness due to personal reproduction and indirect fitness due to additional reproduction by relatives
Inclusive fitness = direct fitness + indirect fitness
Behavior that results in indirect fitness gains is favored by kin selection
Inclusive fitness
0.5
Coefficient of relatedness
parent-child
0.5
0.50.50.5
0.25 + 0.25 = 0.5full siblings
0.50.5
0.25half siblings
0.5
0.5
0.25grandparent - grandchild0.5
0.50.5
0.5 x 0.5 x 0.5 = 0.125cousins
Helpers gain indirect fitness benefits because they are very closely related to their siblings
Helpers at the nest
Florida scrub jay
Parents maximize their fitness by investing in all of their offspring equally
Offspring, in contrast, maximize their fitness by receiving more parental investment than their siblings
Siblicide may increase the fitness of parents as well as the siblicidal offspring if the offspring that is killed is likely to die anyway
Siblicide
Eusociality
3 characteristics:
overlap in generations between parents & offspring
cooperative brood care
specialized castes of non-reproductive individuals
In haplodiploid species females are more closely related to their sisters than they are to their own offspring
(0.5 x 0.5) + (1 x 0.5) = 0.75
sisters
10.5
motherdiploid
fatherhaploid
(0.5 x 0.5) = 0.25
brothers
Eusociality
Eusociality
haplodiploidy does not completely explain the evolution of eusociality
many eusocial species are not haplodiploid
many haplodiploid species are not eusocial