Certain worker ants have an average life span of about a week. In effect, huge numbers of worker ants trade their individual reproductive opportunities for the improved success of the entire colony of their sisters. (3).
There are plenty more examples of animal altruism. The "watchman" bird lets out a squawk every time it sees a hawk approaching, so all the neighboring flocks know when to fly off, thus confusing the predator. The loud squawk makes it a target of attack, while those who heed the alarm get away. As for dogs and wolves, they bring back food for others who have not taken part in the hunt and who didn't risk their lives in finding it. (2).
Another type of altruism is called reciprocal altruism. This is an act performed with the expectation that the favor will be returned. This theory is illustrated by the lives of vampire bats, who rest during the day time in nesting areas in caves or hollow trees. At night they search for animals, such as cows and horses from which they can obtain a blood meal. A bat's high metabolic rate requires it to consume at least 50% of their body weight in blood. If a bat's hunt is unsuccessful on two consecutive nights, they are in danger of death due to starvation. Successful hunters share their food with the unsuccessful and favors are returned when their hunting fortunes change. (3).
Humans often go out of their way to do favors for others and some may wonder why they feel the need to aid a complete stranger. Yet, human altruism holds many topics of debate such as, whether or not human beings can behave altruistically and expect nothing for themselves and how humans have socially evolved to become so different from all other species. Some may refer to human altruism as "the great paradox." "Human altruism is a result of a combination of genetic and cultural influences." This statement is valid because if altruism is a universal phenomenon, then it must be genetically connected to humans.