Simplistic interpretations of traditional evolutionary theory suggest that animals are never altruistic (selfless). In other words their only compelling drive is for personal survival. There are, however, examples in the animal kingdom of "reciprocal altruism", when an altruistic act is carried out, which may be returned at another time. Warning calls by a bird, for example, put the bird at higher personal risk, but the bird will benefit in the long run if others reciprocate. In this case, "altruism" has clear paybacks for the bird.