Altruism – is “self-sacrificing” behavior

Altruism lower’s the helper’s reproductive success while increasing the reproductive success of the individual being helped.

Many insects like ants, termites and bees are sterile and do not reproduce

  • So, how can individuals pass on genes if they can’t reproduce? 

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 has a 50% chance of segregating into a particular egg or sperm.

Degree of genetic relatedness to “self” in a diploid organism.

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Direct Selection: acts on traits that promote success in personal reproduction 
Direct Fitness: a measure of personal reproduction (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 actions

• rb – the coefficient of relatedness between the altruist and the extra individuals

• C – the number of offspring not produced by the altruist

• rc – the coefficient of relatedness between parent and offspring










Ducks by Anne Worner is licensed under CC BY-SA 2.0)

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