Altruism: self-sacrificing behavior where an individual permanently loses opportunities to
produce offspring of its own because it helped another.
Altruism is a Darwinian puzzle: How is this behavior not lost over time if it is detrimental to one’s
reproductive success? Possible explanation: By helping your relatives, you are increasing your
own fitness if their young survive. Coefficient of relatedness: the probability that an allele in
one individual is present in another because they both inherited it from a common ancestor.
Kin Selection: Altruism supplied to relatives other than offspring.
Direct fitness: Fitness gained through personal reproduction
Indirect fitness: Fitness gained by helping non descendent kin survive (ie. Kin selection)
Inclusive fitness: An individual’s total contribution of genes to the next generation as a result of
both of the above.
Hamilton’s Rule: A rare allele for altruism will become more common only if the indirect fitness
gained by the altruist is greater than the direct fitness it loses as a result of its self sacrificing
Inclusive Fitness and the Pied Kingfisher: Some males can’t secure mates and become primary
helpers by protecting their MOM’s nests. They could also act as secondary helpers (protecting
other, non related, couples) or delayers (wait till next year). Primary helpers work harder than
the other two groups. Primary benefit more because the indirect gain is greater than the direct
Examples: Jays. In one species that lacks helpers, breeding individuals have high prolactin levels
while non breeders have low levels. It has been shown that in non breeders in a related species
which DOES have helpers, prolactin levels rise even though they are not breeding. This is
priming the non breeding individual to act as a helper. Helpers get some
o direct gain because they sometimes get to use the same nest that their parents built.
There is also
o indirect gain:
siblings survive. Another indirect gain:
parents may survive longer due to the additional care given by the helper to the
nest (so even more siblings can be made).
In the above species, an experiment was done where helpers were experimentally removed
from nests. The reproductive success of the couple reduced by 50% when helpers were
removed, so helpers are vital.
Facultative altruists: helpers who CAN become breeders but choose to remain as helpers
because they are not able to secure a high quality nest themselves to breed. Test
experimentally: if young birds remain on their natal territories because they cannot find suitable
nesting habitats, then yearlings given an opportunity to claim good open territories should
promptly become breeders. Hypothesis was supported in an experiment with warblers. The Evolutionary History of Helping at the Nest: Helping systems are relatively rare. One
scientist: evolution of helping tied to environmental factors. If environment is unstable, then
helping occurs because it may be too dangerous to start your own nest.
Transactional Theory of Social Behaviour: Members