Later came breeding between different types and sizes of dog for aesthetic reasons as well as for very specific requirem近代犬类的养殖开始逐渐向美学范畴和精确的需求发展，比如小型的梗类犬，杰克罗素，被用来发现地下采石矿；小型玩赏犬，北京哈巴狗，被人们用来暖手；还有大型的犬，藏獒，用来护卫。