Score One for Monogamy

All in the family.
Wasps form eusocial groups, as do ants and bees.

William Hughes

Swingers take note--monogamy may be the foundation of cooperative societies, at least for insects. Researchers have found that bees, wasps, and ants live in communal groups because all members of the group are closely related. The finding challenges a theory recently proposed by one of the world's most eminent scientists.

Some insects, such as ants and bees, live in "eusocial" groups, in which different members carry out specialized jobs to help maintain the colony. Among ants, for example, queens lay the eggs, and workers search for food and protect the colony. The arrangement requires a good deal of sacrifice, especially on the part of the workers, who forgo the chance to reproduce. In the 1970s, Harvard University sociobiologist E. O. Wilson proposed that eusocial communities evolved because they were one big, happy family: The workers didn't mind being celibate because they closely shared their DNA with their sisters, some of whom would eventually become queens and mate, passing on these genes.

However, in 2005, Wilson questioned his own theory, arguing that kinship was not the key to these societies. Instead, he proposed that eusociality evolved because the benefits of group living, such as increased food and defense against predators, were strong enough to induce unrelated insects to band and breed together. Close kinship was not the source of insect eusociality but simply a byproduct, Wilson argued. The concept "shook the bedrock" of the sociobiology field, says William Hughes, a biologist at the University of Leeds in the U.K.

Hoping to test Wilson's new theory, Hughes and colleagues constructed a family tree of 267 species of eusocial bees, wasps, and ants. For each species, they also identified whether females were monogamous or polygamous--in the former case, any offspring would be highly related, but for the polygamous females, their offspring would be less related. When Hughes's group examined the distribution of monogamous versus polygamous species among the eight branches of the family tree in which eusociality had independently evolved, the researchers concluded that each branch had started with a monogamous species. That challenges Wilson's theory by suggesting that blood ties are indeed what get eusocial groups started, the team concludes in tomorrow's issue of Science.

The study's conclusions are getting mixed reviews. "It's an important paper because it provides the first real test for the role of relatedness in the origin of eusociality and its actual evolution," says biologist Bernard Crespi of Simon Fraser University in Burnaby, Canada. "It's kind of a landmark." But Jamie Hunt, a zoologist at North Carolina State University in Raleigh, says the work has "serious shortcomings," showing only that monogamy correlates with eusociality without necessarily causing it. And Wilson isn't ready to abandon his theory, either: "These authors are outstanding researchers," he says, but "they do not prove that [monogamy] predisposes species towards eusociality."

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