Five Thousand Heads Are Better Than One
What ants teach us about the evolution, anatomy, and chemistry of social brain
James Traniello doesn’t like to play favorites. For almost 40 years, Traniello, a professor of biology at Boston University, has devoted his life to the study of ants, investigating their extraordinary social lives. And like a father describing his children, he finds each species wonderful in its own way. But when pressed, he admits to having “a thing” for Oecophylla smaragdina, the Australian weaver ant. These green ants make their homes in rainforest canopies, building elaborate nests. Worker ants (all female) form living ladders with their bodies between adjacent leaves, pulling them together. When the leaves touch, the ants sew them together with silk squeezed from larvae like toothpaste from a tube. (The larvae don’t seem to mind.) The result is a durable nest about the size of a football, built in less than a day. The process is a remarkable display of the cooperative behavior that makes ants—by their sheer numbers and richness of species (about 20,000 at last count)—one of the most dominant social organisms on the planet. That’s part of the reason for Traniello’s crush on the weaver ant, but it’s not the whole story.
“They’re also renowned for their territorial behavior,” says Traniello. “If you look at them in the lab, they stop and look at you. They stand up, open their mandibles, raise their gasters, and threaten you.” Traniello pauses for a moment, considering an ant the size of an eyelash facing off against a human. “That’s pretty gutsy. It takes a lot of ovary to do that.”
Ant and human, eyeball to eyeball. We are linked with the ants in ways both surprising and profound. Humans, as you may have guessed, are the other dominant social organism on the planet. Both ants and humans divide labor and form complex social networks. Both work in groups to accomplish tasks—leaf nests, Mayan temples—that no individual could complete alone. Both raise children in families. Both use the same class of neurotransmitters—“biogenic amines” like dopamine and serotonin—to govern behavior. We both go to war.
There are differences, of course, and here’s a big one: humans build skyscrapers and societies with brains that are large relative to their body size. Ants weave nests, navigate dark forests, and even farm food with brains that are downright diminutive. This may not seem surprising at first, but consider this: only a measly two percent of insects—ants, bees, some wasps and termites—live in societies. Most insects are like fruit flies, buzzing around, doing their own thing, every fly for himself. So the ultra-social ants, operating with brains up to 600 million times smaller than humans, made even Charles Darwin step back in awe. “The brain of an ant is one of the most marvelous atoms of matter in the world,” he wrote in 1871, “perhaps more so than the brain of man.’’
How can ants do so much, with such tiny brains? That leads to the central question of Traniello’s research: How does collective intelligence influence brain evolution? And how does brain size and shape and neurochemistry relate to social behavior? In 2014, he and his collaborators received, along with collaborators Corrie Moreau from the Chicago Field Museum and Wulfila Gronenberg at the University of Arizona, a four-year, $1.44 million grant from the National Science Foundation to continue his work comparing the size and structure of ant brains and how they relate to their complex social organization. The grant will allow his research team to continue unraveling the natural history of the ant, which will ultimately lead to insights into the evolution and neurobiology of all animals that form societies. Including, maybe, us.