Do you spend time with your family? Good. Because a man that doesn’t spend time with his family can never be a real man.
–Don Corleone (The Godfather)
It’s all about family, kin selection is the explanation given for behavior that decreases the ability of an individual to have offspring while increasing that of the individual’s family. The most extreme examples of this is found in eusocial insect species such as ants and bees where entire segments of the population give up their “reproductive rights” in order to tend to those who do the reproducing for them.
Of course the ants don’t get together and decide who gets to breed and who doesn’t, that decision is made by the interaction between their genes and the environment they are exposed to. The point is those genes can be selected for under the right circumstances. In species like bees where the colony is mostly composed of the progeny of a single queen the population are essentially all siblings each sharing a significant amount of their genome. In this case they are more closely related to each other than they would be to their own offspring whom would only share 50% of their genes. From the point of view of continuing the genetic line therefore their efforts are better spent raising more siblings than going off on their own to have children outside the colony.
For other animals the genetic payoff isn’t as high but the same principles still apply, why do some animals invest time helping to rear the young of brothers and sisters or children? Because it serves their genetic interests to do so. There is an hypothesis that male homosexuality in humans is this sort of kin selection trait. There is evidence that the genes that confer homosexuality on males increase fertility when they are in a female host, and having homosexual relatives may (there isn’t much evidence for this) increase the pool of helpers mothers can draw on to raise their young. Speculative but fascinating.
So in light of kin selection it becomes less mysterious to explain concepts like altruism, fundamentally altruism means performing actions that benefit another individual at a cost to yourself. If in the environment your genes evolved the individuals you are most likely to meet are your own family members then it is not really a cost to your genetic line to help them. So it makes sense that even though the human population of the Earth has reached the point were you are much more likely to interact with complete strangers on a day to day basis we embody behaviours that compel us to act compassionately towards those around us, that’s the way we evolved and I wouldn’t have it any other way. (Of course I would say that, I’m programmed to)
Yesterday: Sexual Selection Tomorrow: Gene Eye View