In 1959, Soviet scientists embarked on an audacious experiment to breed a population of tame foxes, a strain of animals that wouldn’t be aggressive or fearful of people. Scientists painstakingly selected the friendliest foxes to start each new generation, and within 10 cycles they began to see differences from wild foxes — fox pups that wagged their tails eagerly at people or with ears that stayed folded like a dog’s.

This study in animal domestication, known as the Russian farm-fox experiment, might be just a fascinating historical footnote — a quirky corner in the otherwise fraught scientific heritage of Soviet Russia. Instead, it spawned an ongoing area of research into how domestication, based purely on behavioral traits, can result in other changes — like curlier tails and changes to fur color. Now, the tools of modern biology are revealing the genetic changes that underpin the taming of foxes of Siberia. In a new study, published Monday in Nature Ecology & Evolution, scientists used genome sequencing to identify 103 stretches of the fox genome that appear to have been changed by breeding, a first pass at identifying the genes that make some foxes comfortable with humans and others wary and aggressive.