It turned out that in selecting for docility, Belyaev had also selected for genetic mutations that came with other traits: a domestication syndrome. In particular, he had unwittingly promoted a delay in the migration of the animal’s ‘neural crest’ cells during development. These cells disperse throughout the embryo and give rise to certain tissues within organs such as the skin and the brain. Most of the cells that produce black pigment derive from the neural crest, and it is the paucity of such cells in the head that give domesticated animals their white blaze on the face.
