A study by a group of biologists, ecologists and medical researchers casts new light on a phenomenon farmers have known for years: the less the genetic variety in a crop or a herd, the greater the risk that disease will decimate it. The presence of many species in ecosystems, the scientists report in  Thursday’s issue of the journal Nature, damps a pathogen’s ability to spread among humans.

The research, which involved 13 authors who reviewed dozens of earlier studies in search of common patterns, found that biodiversity tended to decrease the rate at which diseases were transmitted. It supported this conclusion with evidence involving diseases as diverse as West Nile fever; schistosomiasis, a disease caused by a parasitic worm that infects 200 million people in tropical countries; and Lyme disease.