I like "out of the box" ideas and I really enjoyed the post I like this hypothesis by P.Z. Myers about the effects of domestication on animals. When we domesticate an animal species we select for tameness and this means, in effect, we select animals which have reduced adrenal glands as in such animals their stress levels are reduced, they are generally less fearful, and they are more open to socialization.
There appear to be associated side effects. For instance Mouse, rat, guinea pig, rabbit, dog, cat, fox, mink, ferret, pig, reindeer, sheep, goat, cattle, horse, camel, alpaca, and guanaco all show depigmentation (especially white patches and brown regions). Rabbit, dog, fox, pig, sheep, goat, cattle, and donkey have floppy ears while rat, dog, cat, ferret, camel, alpaca, and guanaco have reduced ears.
He suggests that the common factor is linked to neural crest cells during the early development stage.
This would also the fact that domesticated rat, guinea pig, gerbil, rabbit, pig, sheep, goat, cattle, yak, llama, camel, horse, donkey, ferret, cat, dog, and mink have reduced brain sizes compared with their undomesticated relatives.
Myers speculates that is might be the explanation for Neanderthal brains being bigger that ours - in that the difference is due to Homo sapiens being more domesticated!
Of course this is speculation - but the whole article emphasises that evolutionary changes in one feature can have knock on effects elsewhere in the body.