Any adaptation which confers a survival advantage.
Those who found calorically dense foods more palatable had a better chance of living as an obvious example.
Any adaptation which arises through sexual selection.
A peacock’s tail is actually bad for survival in that it hinders the peacock’s ability to escape predators, but ut is a boon for attraction because it serves as an “honest signal”. An honest or costly signal must be handicapping in some manner.
The favouring of the reproductive success of one’s relatives, even at a cost to one’s own survival or reproduction.
First posited by William Hamilton, it is argued that evolution does not operate on the level of the organism, but of the genes. In this sense, as our relatives share our genes, it is within our interest to see them succeed.
A behaviour whereby an organism temporarily acts in a manner which reduces its evolutionary fitness in favour of another organism’s fitness, with the expectation that the other organism will reciprocate at a later time.
This may be the sharing of food with another person in the hopes that if they get lucky and catch large game during hunting in the future they too will share. In the modern day birthdays are an example of reciprocal altruism; on the face of it the mutual giving of gifts results in no net win, but it serves to smooth the relationship and physically exemplifies trust.