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
takes for granted that something that has not been proven to be true is for that reason shown to be false