Tame foxes, quieter brains: the friendliest foxes have fewer neurons in the brain's aggression switchboard

In the 1950s, Siberian scientists began one of biology's most famous experiments: breeding silver foxes purely for tameness. Within six generations the foxes were wagging, whining and floppy-eared — friendliness, evolving in fast-forward. Now Cornell University researchers have looked inside the foxes' brains for the wiring behind it. Comparing nine brains — tame, aggressive and wild foxes — in a study published in Current Biology, the team led by Eirene Markenscoff-Papadimitriou found that tame foxes have fewer of a specific type of neuron, marked by estrogen receptors, in the ventromedial hypothalamus: a hub in the brain's aggression circuit. It is a first map of how selecting for friendliness rewires a brain — and a clue to how domestication, which gave us every dog on Earth, actually works.