Ants, wasps, bees and other social insects live in highly organized “eusocial” colonies where throngs of females forgo reproduction — usually viewed as the cornerstone of evolutionary fitness — to serve the needs of a few egg-laying queens and their offspring. How they got that way has been hard to explaindespite more than 150 years of biologists’ efforts. Many researchers have thought the answer would come down to a complex suite of genetic changes that evolved in species-specific ways over a long time. But new results suggest that a surprisingly simple hormonal mechanism — one that can be found throughout the animal kingdom — may have been enough to set eusociality in motion. Last month, a team of researchers led by Daniel Kronauer, an evolutionary biologist at the Rockefeller University in New York, published a paper in Sciencethat many experts are saying provides one of the most detailed molecular stories to date in the study of eusocial behavior. The scientists found that division of reproductive labor in ants arose when an ancient insulin signaling pathway, typically involved in maintaining …