A study of rabbits in the 1940s convinced many biologists that parthenogenesis -- reproduction without fertilization of an egg -- sometimes occurs in mammals  However, the study' s methods have since been shown to be flawed, and no other studies have succeeded in demonstrating mammalian parthenogenesis
Thus, since parthenogenesis is known to occur in a wide variety of nonmammalian vertebrates, there must be something about mammalian chromosomes that precludes the possibility of parthenogenesis
infers that a characteristic is shared by all nonmammalian vertebrate species merely because it is shared by some nonmammalian vertebrate species