A recently uncovered Washington Post draft revealed that Donald Trump occasionally ponders the evolutionary underpinnings of human sexual behavior. The President-Elect is said to have wondered aloud: “Is it wrong to be more sexually attracted to your own daughter than your wife?”

Yes. Yes it is.

There’s a reason most people balk at the idea of Trump and his daughter Ivanka (sorry, Tiffany) having more than a father-daughter relationship — a rumor that his previous remarks have done little to suppress. If, like he insinuated in a 2015 Rolling Stone interview, he actually wants to have sex with his daughter, he would be violating some of the most basic laws of evolution.

The biological objective of every individual life on this planet is to pass on its genes to the next generation. Doing so, as a human, ensures doing everything that you can to ensure your kids will be healthy — which includes making sure your choice of mate checks out.

Generally speaking, the kids that result from incestuous relationships do not live long or healthy lives. To shed light on Trump’s disturbing contemplation, it is wrong to be more sexually attracted to Ivanka than Melania because Ivanka shares half of his genes, while Melania shares none (as far as we know). The chances that any latent genetic diseases in the Trump bloodline would be magnified if he fathered his daughter’s child.

Let us explain with a quick genetics refresher: If Trump is carrying a gene for, say, alarmingly orange skin, there is a 50 percent chance that Ivanka also carries it. The chances, then, that their child would get a copy of the Orange gene from both parents are 50 percent — much higher than the odds that would result from a relationship that was not consanguineous.

Table of prohibited marriages from The Trial of Bastardie by William Clerke, written in London in 1594.
Table of prohibited marriages from The Trial of Bastardie by William Clerke, written in London in 1594.

It’s for similar reasons that 19th-century European royals, many of whom were offspring of first cousins, had weird, devastating diseases within their family trees: Hemophilia, a disease that blocks the ability to form blood clots, affected the offspring of Queen Victoria and her husband Prince Albert, who were first cousins, and thereby spread throughout royal families across Europe. Similar reasoning has led scientists to think that the Egyptian boy-Pharaoh Tutankhamen had a cleft palate and a congenitally deformed foot because his parents were siblings.

Of course, the nearly worldwide cultural revulsion to incest is rooted in much more complex ideas than the simple magnification of certain genes, though studying its unfortunate biological effects can show us why humans have learned to be grossed out by it. It’s been shown to cause significant psychological damage to individuals, especially kids who are forced into sexual relations with their parents — especially daughters victimized by imposing fathers. These women, according to one study in the journal Professional Psychology, consequently suffer from low self-esteem, difficulty in intimate relationships, and repeated victimization.

Neither Trump nor his daughter Ivanka, diminutively named after her glamorous model mother, Ivana, have spoken out about the list of allegations made about their relationship, so we can’t know for sure whether Trump has actually crossed the incest threshold or is just unable to avoid mentioning his daughter in his consistently sexist rhetoric. What we do know to be completely true, however, is the sense of revulsion we have when we’re forced to think about it.

Photos via Getty Images / Chip Somodevilla