Neural crest
Neural crest cells (NCC) are vertebrate embryonic stem cells that function directly and indirectly during early embryogenesis to produce many tissue types. Because the traits commonly affected by domestication syndrome are all derived from NCC in development, the neural crest hypothesis suggests that deficits in these cells cause the domain of phenotypes seen in domestication syndrome. These deficits could cause changes we see to many domestic mammals, such as lopped ears (seen in rabbit, dog, fox, pig, sheep, goat, cattle, and donkeys) as well as curly tails (pigs, foxes, and dogs). Although they do not affect the development of the adrenal cortex directly, the neural crest cells may be involved in relevant upstream embryological interactions. Furthermore, artificial selection targeting tameness may affect genes that control the concentration or movement of NCCs in the embryo, leading to a variety of phenotypes.