Behavioral Ecology

Direct fitness is the number of offspring an individual produces. Inclusive fitness is the direct fitness plus indirect fitness. Indirect fitness is calculated by the number of related individuals produced multiplied by the degree of relatedness to those individuals.

Figure %: Degree of relatedness to your father's first cousin's child.

From you to your father is r=.5. From your father to his father is r=.5. From your grandfather to his sister (or brother) is r=.5. From your great aunt to her son is r=.5. And from your father's first cousin to his child is r=.5. Therefore your degree of relatedness is .5^5=.03125.

Figure %: Degree of relatedness to a possible cousin

The degree of relatedness through your grandfather is r=.5^4, but there is only a 1/3 probability that this man is your grandfather, so r=(1/3)(.5^4)=.0208.

Figure %: Relatedness is a haploidiploid bee colony with unknown paternity.

The queen is the only reproductive individual in the colony and so you know she is the mother of you, your sisters, and your brothers. Because males are unfertilized, you are only related to your brother through your mother, with r=.5^2=.25. You are related to your sisters through your mother with r=.5^2. Drone A has a 1/3 probability of being your father. He also has a 1/3 probability of being your sister's father. So your total relatedness to your sister is r=[.25 + (.5)^2(1/3)^2] = .28. You are more likely to help your sisters.

The tiger is unlikely to act altruistically toward either. Although both tigers and house cats are part of the large cat family, they are separated by millions of years. The degree of relatedness among individuals of separate species is far too insignificant to affect behavior.