As geneticists would like you to think, perhaps the mother had the "bad mother" gene that caused her pups to be stressful, and then it was passed from generation to generation; it's all determined by genetics.
Como os geneticistas gostam que pensemos, talvez a progenitora tivesse o gene da "progenitora má" que fez com que as suas crias fossem ansiosas, e foi, depois, passado de geração em geração. É tudo determinado pela genética.