Altruism- “Self-sacrificing” behavior

  • Altruism lowers the helpers reproductive success while increasing the reproductive success of the individual being helped

Territories of an Australian Songbird

  • Only territory owners breed, most of the other birds don’t breed but help the others find food, etc.
  • Do they hold back reproduction in order to avoid depleting the food supply for the rest of the species

How does altruism evolve?

  • Who should you be altruistic towards?
    • Your close relatives that you share genes with

Coefficient of relatedness = r

  • The probability that any two individuals will share a copy of a particular gene
  • In a diploid species, any given allele have a 50%chance of segregating into a particular egg or sperm

Direct Selection: Acts on traits that promote success in personal reproduction

Direct Fitness: A measure of personal reproductivity (your own offspring that survive and reproduce

Indirect Selection (Kin Selection): Acts on traits that promote success in the reproduction of nondescendant relatives

Indirect Fitness: A measure of the number of relatives that the altruist helps to survive and reproduce

Inclusive Fitness: Direct + Indirect Fitness (A total measure of the genetic success of an individual)

Hamilton’s Rule

  • Hamilton proposed that an altruistic gene will be favored by natural selection when the indirect fitness gained by the altruist is greater than the direct fitness it loses as a result of its self-sacrificing behavior or:

rbB> rcC

  • B the extra number of relatives that exist thanks to the altruist’s
  •  rb the coefficient of relatedness between the altruist and the extra
  • C the number of offspring not produced by the altruist
  • rc the coefficient of relatedness between parent and offspring
  1. What are Hymenoptera?
    1. ant, bee, wasps
  2. What are some main characteristics of Eusocial species?
  3. What factors led to the evolution of this extreme form of altruism?