Biologists Study Evolution of Animal Cooperation

John Roach
for National Geographic News
July 9, 2003

Survival of the fittest is a simple reality in the game of life. Successful play necessarily requires a degree of selfishness, but across the animal kingdom species have evolved social behaviors. Why? Do they enhance survival?

"Many of us are really fascinated with the wide spectrum of social behavior we see across the diversity of animal taxa," said Janis Dickinson, an evolutionary biologist at the University of California at Berkeley.

A predominant theory of social evolution is kin selection, which notes that it is advantageous for individuals to help their relatives because it increases the number of their shared genes in future generations. An alternative hypothesis is that helpers increase their own survival and future reproduction by cooperating with others, said Dickinson.

While it is true that animal altruists tend to be related to the individuals they help, whether they do so because of kin selection or simply because their neighbors happen to also be relatives has been a long-standing debate among evolutionary biologists.

Two reports in the June 20 issue of the journal Science highlight a few of the key issues surrounding the study of social behavior and offer some insight to how, why, and with whom certain animals opt to cooperate.

The studies' findings diverge regarding the importance of kinship in this phenomenon, prompting Dickinson and colleague Walter Koenig to conclude in a perspective article on these research papers that "progress in understanding social evolution will involve teasing apart the importance of kinship from other forms of selection."

Crowing for Kin

Critics of the kin selection theory argue that social families of moms, dads, brothers, sisters, cousins, aunts, uncles, and so forth are simply a side-effect of the fact that offspring do not stray too far from home when they reach maturity.

If this is truly the case, it leaves open the possibility that kin-based cooperation is merely a consequence of dispersal patterns: Helpers can only help family because family is all that is around to help.

A genetic study of carrion crows (Corvus corone corone) in which males serve as nannies to breeding pairs shows that certain males do stray far from the nest at maturity, but actively seek a nest of their own kin to settle in.

As in other cooperative breeders, carrion crow nannies are usually offspring that do not stray far from the nest and thus have no choice between helping relatives or unrelated individuals.

However, after about two years some young—mostly males—eventually disperse and when they do they tend not to settle on neighboring territories, according to the study authors Vittorio Baglione, Daniela Camestrari, and Jan Ekman of Uppsala University in Sweden and José Marcos at the University of Sevilla in Spain.

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