What is it about incest that both disgusts us and intrigues us?

Let’s tackle disgust first. Sexual attraction between close genetic relatives has been a nearly universal taboo, at least for us mere mortals. And there is good reason why we find incest repulsive. Over evolutionary time, when it came to having sex, those of our ancestors who steered clear of genetic relatives tended to have healthier, more numerous offspring. This resulted in the evolution of brain mechanisms for avoiding incest.

If this is true, then why do events of incest occur today and in times stretching as far back as the Egyptian and Roman empires? It would seem a biological account is wrong. But before we throw the baby (with two heads) out with the bath water, we must consider how incest avoidance works.

Enter Westermarck.

Edward Westermarck, a Finnish social scientist, proposed over a century ago that childhood experience was necessary for the development of incestuous aversions. Westermarck explained how we figure out who counts as kin, specifically siblings. In each of our minds is a system that identifies likely siblings by tracking which other kids one’s own parents cared for—fed, bathed, scolded, and soothed. So living with another child from birth is one way we “figure out” who’s a sibling. And when it comes to choosing a mate, people we’ve grown up with tend to be the last people we’re attracted to sexually.

This mechanism explains the absence of incest among sibling pairs in humans and many non-humans alike. It also explains why even genetically unrelated individuals raised together are rarely attracted to one another. Adopted siblings and children raised in a communal fashion, such as the co-reared peers of the Israeli kibbutz, tend not to marry one another and, more than this, develop strong sibling-like aversions; childhood co-residence breeds sexual contempt.

Does Westermarck explain Westeros? It’s unclear. For Cersei and Jaime’s intense sexual attraction to align with normal functioning human mental capacity, they would need to have been raised apart, at least for some portion of their childhood. It’s either this or they have lesions to neural circuitry regulating both kin detection and disgust. Since their back story is one of close childhood association, then we’re just going to have to chalk this up to artistic license (or consulting with the wrong anthropologists).

As for Jon Snow and Daenerys Targaryen: To each other, they are effectively strangers. There were no cues that would ever have allowed them to “figure out” and correctly classify each other as kin. Even when they eventually (?) learn they are nephew and aunt, such linguistically conveyed knowledge is unlikely to sway their feelings. (Imagine learning your spouse was actually your sibling. That would likely not change your sexual attraction toward them, but it might make you think twice about having children.) Natural aversions require exposure to the childhood cues of relatedness.

So if all of us have intact incest avoidance systems, why in the world do we enjoy watching this stuff? Don’t worry; there is likely nothing wrong with you if you’re intrigued by the incestuous relationships on “Game of Thrones.” Like moths to the flame, humans have a tendency to seek out (and sometimes obsess over) low-frequency, survival-jeopardizing events. Rubber-necking on the highway to catch a glimpse of guts and gore; peeking through your fingers while watching Saw; telling a friend, “Jeesh that sounds awful—tell me more.” We tend to enjoy learning about the circumstances of abnormal behavior.

But there is another reason why we enjoy watching two hot actors in a sex scene. Oh yeah—they’re two hot actors. And, after all, they’re not our relatives!

Still, there are large individual differences in the reaction to incest—actual or fictive. For men, biologically speaking, there are lower costs associated with having sex with a relative. A man can sire a child with a sister, mother, or aunt, but not lose out on siring a child with another (and then another) unrelated woman. Not so for women. Because women invest far more in the production and initial rearing of offspring, women are much more selective when it comes to (sober) sexual encounters. So while most men likely love the incest scenes (after all, they involve beautiful women), most women are probably not as warm to the idea of incest, no matter how perfectly shaped Jon Snow’s bum is.

Another difference that we can’t ignore is one’s own family composition. It ends up that the strength of one’s personal disgust toward having sex with one’s own sister or brother affects how morally wrong sibling incest is perceived to be in general. So people with no opposite sex siblings tend to express lower personal disgust and less moral opposition to third-party sibling incest a la Jaime and Cersei. On the other end of the spectrum, people with many opposite sex siblings tend to shudder at even the slightest whiff of sibling incest and hold strong moral views against such acts.

There are good reasons why we find incest both disgusting and delightful. As with most things, context matters. Though an “instinct,” our incest avoidance system depends critically on social information, like childhood co-residence. It isn’t clear whether Westermarck applies to Westeros; after all, fiction need not align with reality. But this is the attraction. A little disgust is one way “Game of Thrones” will stay in our minds—a fact producers are perhaps counting on.

Debra Lieberman is associate professor at the University of Miami, Department of Psychology and co-author of the forthcoming book, Objection: Disgust, Morality, and the Law, to be published in 2018.