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.
Tal como los genetistas quisieran que piensen, tal vez la madre tenía el gen de "la mala madre", que causaba que sus crías fueran estresadas, y luego pasó de generación en generación; todo está determinado por la genética.