There are many ways to examine the social worlds of fact and fiction, and whether or not they are similar. In an article for* The Atlantic*, I examined the social networks of superheroes, a mathematical way to think about comic books. I found that the worlds of fiction are not so different from the real world, at least when it comes to our social ties.

But we can go beyond social network analysis to understand other ways in which there might be similarities between the social worlds of fact and fiction. Specifically, in additional to our social interactions, we also have our familial ties: who’s related to whom.

And mathematics can provide a way to examine this. There is a mathematical formula, from the field of population genetics, that allows us to calculate something known as the inbreeding coefficient. The inbreeding coefficient is, simply put, a measure of how inbred individuals are. If your father is also your grandfather, you have a high inbreeding coefficient. Or, in a less extreme case, if your parents are first cousins, you’re inbreeding coefficient is about one-sixteenth. Hatshepsut, an Ancient Egyptian pharaoh, had an inbreeding coefficient of 25 percent. Curiously, the scientist who invented this quantity, Sewall Wright, himself had a rather high amount of inbreeding in his own family.

But this technique can also be applied to the fictional world in addition to the real world. And this can allow us to see how similar our own mating habits are to imaginary characters and whether or not fiction is really all that different from our everyday lives. So where to look?

To the world of superheroes! Here we have a handy family tree of various members of the X-Men, created by Joe Stone. While certainly not complete–no family tree is exhaustive–this does allow us to perform a simple examination.

And according to my calculations, there is no inbreeding whatsoever among the X-Men! Despite the clones, immortality, and occasional mind control of comic books, the X-Men lack inbreeding, at least according to this chart. If we delve a bit deeper though, it turns out that the twin children of Magneto do have a sexual relationship. While no children have resulted from the union of the Scarlet Witch and Quicksilver, this would have resulted in an astonishingly high inbreeding coefficient of 25 percent, similar to a Pharaoh. The only situation I am aware of in the superhero world where there is a non-zero inbreeding coefficient is that of Bart Allen, also known as Kid Flash. Allen is descended from the Flash (Barry Allen) on his father's side and the Flash's twin on his mother's side. However, this genetic similarity is separated by many centuries (Bart Allen lives in the Thirtieth Century, after all), that makes the inbreeding coefficient, while non-zero, very low.

The upshot is that superheroes have far less inbreeding than other examples of fiction, such as William Faulkner's Compson family. In fact, they seem to have even less inbreeding than most of the "real world," from the extreme examples of Ancient Egypt to the more subtle cases of the European royal families.

This is not to say that the superhero world is normal. The Scarlet Witch, while never having children with her brother, did have imaginary children with an android. However, while we think of the world of comics as being contrived and a bit strange and weird, when it comes to inbreeding, it seems that the X-Men are no more inbred—and in some cases, significantly less inbred—than the "real world."

Top image: jdhancock/Flickr/CC-licensed | Thanks to Jacob Kramer and Ari Kahan for comic book expertise