There is most likely an element of that mate. A silver fox program in Russia set out to breed calmer ,more easily handleable foxes that would also breed better, being more placid. That's when the pendent ears and collie marking came in. I don't know how it works exactly , but scientists found that the hormone , or whatever it was that causes the fear and nervousness in wild animals diminishes when you selectively breed for calmness. Now apparently this is also used in the assimilation of colour and other genes as well. I believe they also bred short legged foxes. That program was abandoned bec