“Kissing Your Sister,” or, Musings on the Fitness Consequences of Consanguineous Mating | Vol. 4 / No. 20.3

Ah, Biblical literalism.

So I don’t know if you’re Christian, or if you ever were, but the facts of the historical compilation of the books of the Old Testament (that’s mostly the same thing as the Tanakh… I’m not going into that much depth today but you can read about that here) make things a little awkward if you take events literally.

Note now, before we begin, that you do not have to take a thousands-of-years-old religious text literally. Just that some do. No I don’t know why.

Anyway, “Young Earth Creationists” like Kenneth “Makin’ Bacon” Ham do just this, and it is at this point that we get to the problem: incest. Adam and Eve being the first humans from whom all other humans are descended means that the only people their kids would have had to marry were each other.

This isn’t ideal, for a whole host of reasons—just look at the Habsburgs. Creating a population out of just two individuals would compound all sorts of genetic issues. Freud called it one of only two “universal taboos” (along with patricide). The whole human population would be paddling in the shallow end of the gene pool forever. A whole lot of people simply wouldn’t be able to have kids because they’d be functionally sterile.

Of course there are always mental contortions you can make, like assuming Adam and Eve were so genetically perfect that no problems would arise (have you got a moment to spare for the great goddess Lacuna?), but even so it leads to some pretty odd answers. Take this answer from Kenneth “Pass the Pork” Ham’s website “Answers in Genesis.” The question is, as Eleanor Ann Arroway (and many a Sunday schooler like my once-young self) asked: “Where did Mrs. Cain come from?”

See, Adam and Eve have two kids, Cain and Abel. Cain kills Abel, for reasons unspecified, and is exiled to the Land of Nod, where he marries. Who does he marry? Are there other humans? Maybe they’re the descendants of the fallen angels from the Book of Enoch that only sort-of finds its way into Genesis chapter 6? Not according to Ken:

If we now work totally from Scripture, without any personal prejudices or other extrabiblical ideas, then back at the beginning, when there was only the first generation, brothers would have had to marry sisters or there wouldn’t have been any more generations!

See? Simple. If we want the human race to exist you have to marry your sibling, silly! It’s not like God could have made more people or anything. He even adds an exclamation mark to make sure we get it, I guess. And it’s fine because (as I said before) they were genetically perfect. It’s only bad to have kids with your relatives now.

Now I hear what you’re saying—how could genetic diversity have gotten worse than an an entire race created by literally marrying your siblings?but don’t worry, because none of this rests on reason. It rests on the assumption that everything used to be miraculous and perfect and now everything is fallen. It rests on picking your conclusion (the Bible is literally true) and then retrospectively looking for an argument to back it up (inbreeding isn’t a problem, because God). Well, congrats Ham, you found one.

Normally I’d say that’s the end of it, but humans are surprisingly low in genetic diversity, at least compared to some other species. It looks like at some point in our past we were down to as few as a thousand individuals, something called a genetic bottleneck. And at least some scientists think we could repopulate from a population as small as 160 people, which might be a useful number to keep in mind if you happen to be Elon Musk.

Meanwhile the BBC did a fun little romp into the question of repopulating the human race from one couple, and you can go read that if this post made you wonder.

In the meantime, just remember: Leia picks Han for a reason.


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Richard Ford Burley is a human, writer, and doctoral candidate at Boston College, as well as Deputy Managing Editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and futurism here at This Week In Tomorrow.