in animal husbandry this kind of thing is called dysgenic breeding. mixing different breeds and not getting beneficial or desirable phenotypes as a result. black + whatever mix often have jaw and teeth issues. blscks commonly have prognanthism and mixing this with other genes makes it worse. pics of young mutts almost always have braces. the hair is an obvious one, if you wanted crazy unmanageable curly hair great , but most don't. so farmers wouldn't breed them together. iq and behavior are another one, instinct is baked into genes. you don't breed a cane corso and a lapdog, you'll get a crazy mutt who will rip your throat out randomly.
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