At lunch today, one of my coworkers mentioned that he had heard that puppies and kittens in the same litter can have different fathers. We debated whether that is true, and I offered to try to find out. I did a quick search on dogster to see if you had already answered the question, but I didn’t see an entry from you in the search results (although it appears the question has been asked in some of the dogster mating forums, and that everyone says yes). So our question is: is it true that puppies and kittens in the same litter can have different fathers? If so, how is that possible biologically?

We also debated whether human fraternal twins can possibly have different fathers. I recalled that this question was asked by one of my schoolmates during my sex ed class in school, and that the sex ed teacher said yes but that it was very rare. When I told my coworkers this, they laughed in my face. What do you think? Is it possible?

Elizabeth
Washington, DC

Any female who mates with more than one male in rapid succession and then releases more than one egg can host babies with different fathers in her uterus simultaneously. It happens when one male’s sperm fertilizes one egg and another male’s sperm fertilizes a different egg. This is true for all mammals, including cats, dogs and humans.

Female cats are, shall we say, quite promiscuous. If given the chance, most female cats will mate with several males when they are in heat. Therefore it is quite common for feline littermates to have different fathers.

After dogs mate, they become “tied together” for several minutes. This is an evolutionary adaptation that prevents another male from immediately mating with the female. Canine littermates therefore are more likely to share a father. However, the evolutionary adaptation is far from perfect, and it is not uncommon for puppies in a litter to have different fathers.

Human reproduction is not taught in veterinary school. However, there is no reason why we, or any mammalian species, should be different.

Photo: Who’s your daddy?