Hamilton's Model

Hamilton's rule is rb - c > 0. Here c is the cost to the giver's fitness (c fewer offspring because of helping), and b is the benefit to the recipient's fitness (offspring gained by the recipient from the help). Here again, "r" is a measure of the relatedness between giver and the receiver [...] Hamilton’s rule says that for unrelated individuals (r = 0) no benefit can overcome the cost of loss of the altruist's fitness (0 - c can't be greater than 0) and aid giving is selected against...

 Evolutionary Biology and the Punk Scene

Evolutionary biology historically has focused on a particular kind of change in heritable traits. Some traits enable an organism to have more offspring than other organisms in a population. In this way, a heritable trait can become more abundant in the next generation. It's a simiple numbers game. New traits appear first in a single organism (like the debut songs on a pioneering punk album). But they can appear in increasing numbers of organisms with each :h new generation if they help organi...