Superfecundation

SUPERFOECUNDATIO, super imprägnatio, superfecundation, superconception, the simultaneous fertilization of two ova of the same ovulation period. In a broad sense, this term encompasses all dizygotic twins in monotocous animals (and consequently in man). Usually, this term is understood in a restricted sense, as the fertilization of two ova of the same ovulation period by spermatozoa from two different fathers. The possibility of such superconception in animals, especially polytocous ones, is beyond any doubt. Thus, bitches during estrus are often mated with two or even several dogs of different breeds, and their litter may contain strictly identifiable mixed-breed puppies. The same is known regarding cats, rabbits, and sheep. The possibility of superconception has also been proven in monotocous animals. Thus, there are observations that mares covered by a stallion and a donkey produced—in the case of twins—a foal and a mule. As for superconception in humans, such a possibility is entirely admissible and meets no theoretical objections, although there are as yet no strictly proven cases. In the older literature, cases were cited as proof where a woman of one race, having had intercourse with men of the same and another race, gave birth to twins, of which one belonged to the race of one father and the other to that of the other. From a modern standpoint, such observations are not fully conclusive, since one of the twins may inherit the race of the mother and the other the race of the father, while both may have the same father (according to Mendel's law). Thus, for example, a Negro woman may give birth to twins by a white man, of which one may be black and the other white. Such twins would be conclusive in only one case: if a woman of a certain race, having had intercourse with two men of two different races (both distinct from each other and from her), gave birth to twins, and one of the twins turned out to belong to the race of one father and the other to the race of the other father. Such a coincidence of circumstances is quite possible with differing blood group affiliations of the mother and the two fathers. Thus, if a mother belonging to group O were to give birth to two twins, of which one belonged to group A and the other to group B, the sufficiently well-founded conclusion can be made that the twins have two different fathers, i.e., superfecundation is present. As yet, systematic observations and studies in this direction have not been made.