altruism

Altruistic behaviour

An increase in the reproductive output of the recipient of the expense of the “selfless” behaviour of the altruist

Altruism

Helping others to have offspring at a cost to their own reproductive output (parent-offspring = clear cost-benefit relationship)

Kin selection

Relatives commonly help each other to maximise gene contribution to future generations

Direct fitness

Fitness gained through personal reproduction (own offspring)

Indirect fitness

Fitness gained from aiding the survival of non-descendant kin (e.g. siblings) - aid kin’s offspring

Inclusive fitness

Direct + indirect fitness

Hamilton’s rule

The gene for this altruistic behaviour will increase in frequency if the benefits to the recipient outweigh the costs

rBC-C>0

B = benefit

C = cost

r = relatedness

0.5 relatedness

Offspring (descendant), full siblings (non-descendant)

0.25 relatedness

Grandchildren (descendant), half-siblings (non-descendant)

0.125 relatedness

Great-grandchildren (descendant), cousins (non-descendant)