Why do volunteer firefighters rush into a burning building to try to save children from some family they have never met before? Every day we afforded examples of people sacrificing their personal interests for the benefit of others.

But also, biologists usually use a definition of "altruism" that does not include close kin. Richard Dawkins was explicit about this in his 1976 book "The Selfish Gene." Helping someone you are directly related to is not considered altruism.