Campus & Community

Taking a look at how ant (and human) societies might grow

6 min read

Social genes are key to colony growth

E.O. Wilson has learned a great deal about human behavior by studying ants, termites, and bees. (Staff file photo Rose Lincoln/Harvard News Office)

Edward O. Wilson has learned a great deal about life by studying ant societies. In this knowledge, he finds parallels between the social interactions of insects and those of birds, lions, monkeys, apes, and even humans. The last parallel got him into trouble in the late 1970s, but he now enjoys credit for establishing a new field of science – sociobiology, the influence of biology on human behavior.

Now Pellegrino University Professor Emeritus at Harvard, Wilson remains fascinated with the highly organized societies of ants, bees, wasps, termites, and humans. He and Bert Holldobler, with whom he shared a Pulitzer Prize for their book “The Ants,” have published a paper about how such societies originate, which appears in the September 20 issue of Proceedings of the National Academy of Sciences. The original colonies of humans, like those of ants and termites, they propose, could have arisen in much the same way.

Both ants and humans have achieved “spectacular ecological success,” they write. For humans, this includes winning out over competing forms of humanlike creatures who evolved from apelike ancestors. Ant-type societies may be a common reason for such success.

Video: E.O. Wilson discusses his research

The standard theory of the rise of eusocieties, as these evolutionarily advanced colonies are known, credits altruism, behavior that benefits others at the cost of the individual. For an ant, that would mean giving up the privilege of reproduction to become a sterile worker or soldier in the colony. For a human, it might mean fighting a war in a foreign land.

In this model, kinship is key. An individual insect gives up its fitness to foster that of the kin group. The colony is built on close genetic relationships with a push from an environment in which food, water, and shelter are plentiful.

Wilson says that he “once promoted this theory, although evidence for it is sparse. In the last two decades, however, much new and more solid evidence has turned everything upside down.” He and Holldobler now believe eusocial colonies can grow and prosper without such kinships. In fact, biological nepotism could be disruptive, they say.

Social genes prevail

Either way, any colony has to start with genes. These starter genes would be flexible, that is, include versions that aid altruism and thus promote cooperation. When such “social genes” are favored by natural selection, that helps their owners adapt to the environment and prosper.

“Eusociality can originate when founding members of the primitive colonies have low relatedness,” Wilson says. What counts is the social genes, not who is related to whom.

Wilson and Holldobler cite the example of a species of carpenter bee that has reached an early stage of eusociality. These insects form pairs, which then divide into queen and worker roles. Workers or subordinates usually stay if unrelated to a queen, but leave if they are related. Kinship, in this case, serves to weaken, rather than strengthen the colony.

Eventually, eusocial evolution pushes the colony beyond the point of no return. At this level, individual workers living in groups of ants, bees, and wasps no longer show a preference for their mothers in colonies with many queens. Nest-mates share food, groom each other, and recognize their fellows by scent. A chemical communication system arises that is comparable with the audiovisual system of humans.

“Colonies with lower relatedness among the workers often have higher growth and reproduction rates than those with higher relatedness,” Wilson notes. “This effect may be due to improved genetic resistance to disease or to the enhancement of division of labor by genetic proneness to specialization,” but not to kinship relations.

Human possibilities

Despite these advantages, eusocial colonies are rare. Of some 2,600 families of insects and their close relatives, only 15 boast eusocial species. “It follows that nature has set a very high bar for attainment of eusociality,” the researchers conclude. “Additional extraordinary circumstances in their history and in the environmental challenge they faced lifted them over the bar.”

When such conditions exist, natural selection works on the flexibility of genes to provide the best returns for a group versus individuals and kin clans. First would come cooperative breeding that ants are so famous for today, then caste systems, which Wilson and Holldobler call “the defining property of eusociality.”

Colony evolution obviously renders some individuals sterile drudges or self-sacrificing soldiers. But that doesn’t matter, say the researchers, because neither deviants who leave to try their luck as loners nor colonies weakened by kinship squabbles can compete against well-integrated colonists.

Constructing nests and caring for their young are key adaptations that lead to colony success, so is building defenses against enemies, including predators, competitors, and parasites. Complex communication also plays a big role. Signals of fertility status and colony recognition came first. Next came alarm signals and those that lead colonists to food sources. Food trails and territorial limits become established with the aid of scents exuded by the colonists. As an extreme example, Wilson and Holldobler cite colonies of African driver ants, more than 20 million-workers strong, that live in large excavated tunnels and rooms and hunt in armies for a wide range of prey.

“If the conclusions drawn here about eusociality in insects are correct,” the researchers propose, “they could have implications outside the insect world.” For example, their paper cites the eusociety of naked mole rats, hairless rodents that live underground. As mammals, they are much larger brained and closer to humans on the evolutionary tree than ants, termites, and bees.

Wilson and Holldobler go on to speculate that the same rarity of occurrence and group selection of social genes might also characterize proto-humans evolving in Africa. Eusociality could have played a role in the “spectacular ecological success and pre-emptive exclusion of competing forms by Homo sapiens,” they write. In other words, eusociality may have helped modern humans beat less organized competition, such as the Neanderthals.

“We propose this with great caution,” Wilson added. “The evidence, after all, only applies strongly to insects. Human altruism and tight-knit societies may well have evolved differently. But if it is true, it would help us understand the group aggression and warfare so widespread today. Those who study human biology and behavior should take a new look at this possibility.”