tl;dr

There’s a stereotype that male sexual attraction is triggered mainly by appearance, and female sexual attraction is triggered mainly by status.

…Yes I know, this stereotype is grossly oversimplified, and is only valid on the margin, and really there’s overlapping distributions, etc. etc. (+ even more caveats in §1.2 below). But it does have a kernel of truth.^[1]

Now, this post is not mainly about sex differences per se. What I actually care about is the more basic observation that “appearance-based sexual attraction” is a thing that exists in humans, and so is “status-based sexual attraction”. These stem from innate reflexes in the brain. My goal in this post is to speculate on how those innate reflexes might work, focusing on the neuroscientific “symbol grounding problem”.

For appearance-based sexual attraction (§2), I suggest two possible hypotheses. One involves innate sensory heuristics calculated in the brainstem, including visual processing by the superior colliculus. The other involves (what I call) “transient empathetic simulations” connected to the somatosensory system.

For status-based sexual attraction (§3–§6), I suggest a mechanism involving “phasic physiological arousal”. I further propose that this mechanism would also explain various other everyday observations, such as the stereotypical female attraction to tall men.

1. Introduction

1.1 Why am I writing this post?

This post is a little satellite orbiting my mega-post from last year Neuroscience of human social instincts: a sketch. See especially the introduction to that post for background and motivation, including the “symbol grounding problem” in neuroscience.

In short, a “symbol grounding problem”, as I use the term here, is any problem where the brain needs to be wired up to pluck out a particular real-world thing for special treatment: attraction towards healthy food, repulsion from diseased corpses, aggression towards rivals, and so on. As discussed in that post, I claim that these symbol grounding problems are rarely straightforward, for deep reasons related to the structure of learning algorithms in the brain. The solutions are often a bit convoluted, and even then they only sorta work, with various side-effects and misfires that wind up incidentally explaining other aspects of human and animal behavior.

Anyway, human sexual attraction is an example of a symbol grounding problem. Evolution has built humans, like most animals,^[2] to have mating preferences: we find some potential mates to be more appealing than others. The “why” question is textbook evolutionary psychology (“evo-psych”) stuff—better to find a mate who is fertile, strong, well-resourced, and so on.^[3] But that still leaves open the “how” question:^[4] if it’s preferable to have a mate with Property X, then how exactly does the genome build a brain capable of ranking potential mates according to Property X? That symbol-grounding problem is the subject of this post.

1.2 A bunch of caveats

Oh boy does this post need a bunch of caveats:

1. Much of this post is about an aspect of sexual attraction in women, but WTF do I know about sexual attraction in women? That part is alien to my first-hand experience as a cis man (who has been off the dating market for decades). I’m interested in feedback though!

2. #NotAllMen, #NotAllWomen, etc. People vary continuously along many axes, and even if there’s some systematic difference between men and women on average, we’re talking about overlapping distributions. Relatedly, my examples will involve heterosexual attraction between cis men and cis women, since that’s a common situation that I’m familiar with. Some brief speculations about other situations in a footnote→^[5].

3. This will not be a comprehensive theory of sexual attraction, but rather a couple of the many ingredients entering into it. For example, I will propose that “phasic physiological arousal” is an input to female sexual attraction brain circuits. As it happens, if a guy wants to induce phasic physiological arousal in a woman, it’s easy: he can threaten or hurt her. But if he does that, she’s not gonna respond with sexual attraction, she’s gonna respond with pepper spray, and rightly so. The issue is: the sexual attraction brain circuit has lots of other inputs too, including (I believe) things like “the woman sees the guy as a friend rather than an enemy”.^[6]

4. Relatedly, I’m talking about particular (hypothesized) innate reflexes, i.e. things in the same category as involuntarily orienting to a sudden loud sound. One innate reflex does not constitute destiny. One innate reflex does not determine how people will actually behave (since that also depends on many other aspects of their brain, life, and culture). And one innate reflex sure as hell doesn’t determine how people “should” behave—see Naturalistic Fallacy.

5. I’m assuming that certain pop-culture stereotypes, for example the idea that women tend to feel attraction towards taller men (other things equal), are indicative of timeless human universals, as opposed to being specific to my own culture. I have some reasons to believe that, but didn’t thoroughly scrutinize the literature in every case. Please comment if you think I’m wrong about any of those assumptions, and we can chat about it.

1.3 Relation to prior literature on the neuroscience of human sexual attraction triggers

Very little. I wrote this post quickly and without thoroughly studying what people have historically written on this topic. (Please share in the comments if you know something important that I’m missing!)

I have lots of strong opinions about how the brain works in general, and if you’re interested in how those particular opinions intersect the topic of human sexual attraction triggers, then read on! If you’re instead interested in broader academic thinking on this topic, then you’re in the wrong place; maybe instead try this 50-page book chapter by Adam Safron and Victoria Klimaj.^[7]

2. Part A: Appearance-based sexual attraction

Both men and women (but typically with a higher weighting in men) can feel sexual attraction based on someone’s appearance.

There’s an evolutionary “why” question, with a well-known evo-psych answer: appearance offers various types of evidence about the suitability of a mate—their health, age, genes, hormone profile, and so on.

On to the “how” question: how does appearance-based sexual attraction work in the brain?

In the case of female-typical sexual attraction, my current guess is that appearance-based sexual attraction is largely (or entirely?) indirect. I’ll discuss one example in Part B below: appearance can trigger phasic physiological arousal, and the phasic physiological arousal can in turn trigger sexual attraction. I think this is the explanation of typical female attraction to tall guys (§4.1). Another indirect pathway (maybe) would go through valence: I think there’s an innate reaction that makes it pleasant to look at symmetric faces, and then positive valence (“liking / admiring”) is one of several contributors to female-typical sexual attraction. (…Or maybe the symmetric faces thing is direct, I dunno.)

However, in the case of male-typical sexual attraction, I definitely think the direct route (appearance → sexual attraction) plays a huge role.

How does that direct route work neuroscientifically? This part of the post will be pretty short, just because I don’t have much to say about it. But where I’m at right now is these two (non-mutually-exclusive) hypotheses:

2.1 Hypothesis 1: Sexual attraction triggered by direct innate sensory heuristics in the brainstem

For example, I think the brainstem superior colliculus has a set of innate visual classifiers, which can detect slithering snakes, skittering spiders, and various other ecologically-relevant inputs. Likewise, the inferior colliculus can detect innate auditory patterns that merit particular responses, and so on with all the other senses.

Thus, there could be innate heuristic detectors of this type which directly link to sexual attraction circuits.

See Neuroscience of human social instincts §1 for further discussion.

2.2 Hypothesis 2: Sexual attraction triggered by transient empathetic simulations of somatosensory inputs

A more exotic way that direct appearance-based sexual attraction might work in the brain is:

Transient empathetic simulation of somatosensory inputs allows the brain to solve the “symbol grounding problem” for thinking about the size, shape, and features of someone else’s body.

Yes I know, that previous sentence is probably incomprehensible. But if you go through Neuroscience of human social instincts: a sketch, and replace “interoceptive inputs” with “somatosensory inputs” in §4 of that post,^[8] you’ll hopefully get what I’m talking about.

Once the brain has pulled out data about the size, shape, and features of somebody else’s body, those data can in turn feed into a set of innate heuristic estimators tuned to pick out conspecifics of the appropriate age, shape, fertility, and so on.

(…Or something like that, I’m still a bit hazy on the details.)

3. Part B: Sexual attraction from phasic physiological arousal (esp. in women)

On to the lion’s share of the post!

3.1 Terminology

“Physiological arousal” is a nervous system response, coordinated by the locus coeruleus, that can be measured via heart rate, skin conductance, pupil diameter, and so on. It activates in high-stakes situations, and puts long-term investments on hold in favor of optimal performance right now.

“Phasic physiological arousal” would be a fast jump in physiological arousal. The opposite of “phasic” is “tonic”.^[9] In the context of this post, phasic arousal = a transient jump in physiological arousal that happens at precisely the same moment that we think about (pay attention to) Person X.

3.2 Headline hypothesis

When a woman experiences phasic physiological arousal upon noticing or thinking about another person—when the person seems “attention-grabbing”, “imposing”, “intimidating”, “larger-than-life”, etc.—that plays a major role in causing her to feel sexual attraction towards that person.

(It’s dead obvious that women can feel physiological arousal in conjunction with feeling sexual attraction. My non-obvious claim here is that the physiological arousal can be the cause, and the sexual attraction can be the effect, in addition to the other way around.)

I'll jump right into two central examples in §4, then discuss why I think this is both neuroscientifically and evolutionarily plausible in §5, then in §6 I’ll circle back to more interesting and speculative everyday examples and implications.

4. Central examples

4.1 Tall guys

I think we have an innate reaction that induces physiological arousal upon noticing a tall person, just as many other animals have instincts to “size each other up”. The evolutionary logic is: Any interaction with a tall person is high-stakes, because they could potentially beat us up if they dislike us, and they could potentially beat up our enemies if they like us. As for the neuroscientific mechanism, see the parallel discussion in §2.

So that ties into the stereotypical female attraction to taller men.

I acknowledge that I haven’t provided any direct evidence here that the pathway is “height → physiological arousal → sexual attraction”, instead of more direct “height → sexual attraction” (as in §2). But the former is at least an elegant story that fits in with other things I believe. For example, I think (most straight cis) men have the height → physiological arousal response towards other men, leading to deferential behavior, but without the sexual attraction part. (See §5.1 below.)

4.2 Guys with fame, power, and status

Here, it’s not a direct innate reflex that triggers physiological arousal, but rather knowing (and viscerally feeling) that the person is in a position to strongly impact my life, for better or worse. That makes the situation high-stakes, and high-stakes = physiological arousal.

Why might the person be in a position to strongly impact my life? It could be for any of a million reasons. Maybe they’re rich, maybe they’re famous, maybe they’re powerful, etc. And that leads to the stereotypical female attraction to men with fame, power, and status.

Mentioning “status” is almost tautological, because (I claim) “I think of Person X as high status” is almost synonymous with “I experience phasic physiological arousal upon noticing or thinking about Person X”. More on that next:

5. Details, neuroscience, and evolution

In my neuroscience work, I subject these kinds of hypotheses to three hurdles: Is it neuroscientifically plausible? Is it evolutionarily plausible? And is it compatible with data and observations, including everyday experience? “Everyday experience” is covered in §4 above and §6 below; here I’ll quickly address neuroscience and evolution.

5.1 More on the neuroscience

The last time I wrote about phasic physiological arousal was Neuroscience of human social instincts: a sketch. There, I suggested that there’s a circuit in the brain upstream of compassion, spite, and a “drive to feel liked / admired”, among other things. And I suggested that the phasic physiological arousal associated with a person is basically a multiplicative factor going into this circuit. For example, it feels good to be complimented by some random kid, but it feels much better to be complimented by a celebrity you idolize.

The more that I see Person X as high-status (either prestigious, dominant, or both), the more phasic physiological arousal I’m likely to experience when I see them or think about them, and the more I’ll care about the interaction going well.

(See my post Social status part 2/2 for more on prestige and dominance.)

For a typical cis man like me, that’s the whole story. If Person X has high status in my eyes, I’ll overthink all my interactions with them. If they go well, I’ll pat myself on the back, even years later. (See here where someone describes their “feelgood” email folder to look at when she feels down. Most of the examples involve her getting complimented by people who she sees as important and intimidating.) Likewise, if the interaction goes poorly, I’ll feel unusually awful.^[10]

But for me (a cis man), that dynamic has no relation whatsoever to sexual attraction, except in the opposite direction (sexual attraction can make an interaction feel high-stakes). I think this is a difference between most cis men and most cis women.

So anyway, I view this hypothesis as highly neuroscientifically plausible, in that if you buy all the stuff I wrote in Neuroscience of human social instincts: a sketch, you’re 99% of the way to a phasic physiological arousal → female sexual attraction reflex in the brain. You would just need to add on ≈1 more point-to-point connection between hypothalamic cell groups.

5.2 Evolutionary plausibility

If interacting with Person X feels viscerally high-stakes to me, it means that Person X is probably in a position to strongly impact my life, for better or worse. As I mentioned above, regardless of my gender, I’ll feel an unusually strong drive to want Person X to like / admire me. Evolutionarily, that makes a lot of sense!

By similar logic, if I’m a woman, and Person X is in a position to strongly impact my life, for better or worse, then that’s a sign that they’d make a good mate, other things equal. They probably have social capital, strength, and other resources. If I marry him (or hook up with him), then he’s likelier to apply those resources towards my wellbeing, and to the wellbeing of our children. And if everyone else in our hunter-gatherer band wants to curry favor with the father, then they’ll be generous towards the child too. And if the children are similar to their father, then they’ll be likelier to eventually wind up with power and resources of their own. All these things are good for inclusive genetic fitness. So this all seems evolutionarily plausible (as one of many inputs to sexual attraction).

Last but not least, why is this disproportionately a thing for women? Wouldn’t men likewise benefit from marrying or impregnating a woman who commands a lot of social capital and other resources, resources that they can then use for raising children? And yet, per Steven Pinker, “a middle-aged congresswoman does not radiate the same animal magnetism to the opposite sex that a middle-aged congressman does”. What’s the deal?

…This is a bit outside my wheelhouse. There are evo-psych people who read cross-cultural studies, who think about life in Pleistocene hunter-gatherer tribes, and who puzzle over evolutionary game theory and sexual selection. Those people say that in equilibrium, men are selecting women more on health, youth, and fertility, and women are selecting men more on the ability to command resources, on the margin. I don’t have a good command of the details, but OK sure, whatever, seems like the kind of thing that could be true.

6. Other everyday things that the “phasic physiological arousal [coincident with paying attention to a person] → sexual attraction” theory might incidentally explain

(These are all more speculative.)

6.1 “Friend zone” / “Nice guys finish last”

As the pop-culture stereotype goes, a woman can feel very safe around a nice guy, without any sexual attraction. The interactions feel low-stakes to her. Low phasic physiological arousal.

6.2 Reduction of female sex drive in long-term relationships

This fits in with physiological arousal because, if you’ve known someone a long time, you get used to them, and your interactions with them feel lower-stakes. Even if the interactions are still high-stakes in some objective sense, you’ll get desensitized in practice. I expect that spouses of rock stars, presidents and so on likewise settle into their routine and stop having a visceral feeling of “oh jeez I’m talking to the president”.

6.3 Women are less likely to make the first move

There’s clearly a lot that goes into this phenomenon, including cultural factors, but I suspect that at least one contributor is: if someone displays interest in you, that is itself a source of physiological arousal. So (I think) a woman can kinda “discover” that she’s into a guy only when the guy starts flirting with her—and it’s actually partly because he is flirting with her.

6.4 Women tend to feel attracted to guys who make them laugh

Note that someone can want a partner who makes them laugh even if that’s not directly related to sexual attraction. Relationships are not just about sex, but also about enjoying a person’s company, and so on. So unsurprisingly, people of all genders want relationship partners who make them laugh. However, if we’re talking about sexual attraction in particular, my current impression is that the connection is stronger in typical women, i.e. that women tend to feel sexually attracted to men who make them laugh, more so than men feel that way towards women who make them laugh.

Insofar as this is true, I can think of two possible stories explaining it. They’re not mutually exclusive, and indeed my money would be on both being true:

Making-me-laugh and sexual attraction have a common cause: Laughter is triggered by physiological arousal in conjunction with feeling safe—see A Theory of Laughter. And those very same triggers contribute to sexual attraction.
Making-me-laugh is upstream of sexual attraction: The laughter reflex itself causes physiological arousal (just as it causes pleasure, and causes spasmodic breathing, and so on), which in turn can contribute to sexual attraction.

6.5 Sexual fetishes

I don’t think there necessarily has to be perfect correspondence between what makes you feel attracted to a person at a party, versus what gets you off in the sack. And this post is about the former, not the latter. So maybe this section is off-topic?^[11]

…But for what it’s worth, it seems worth noting that a bunch of sexual fetishes seem to involve situations that trigger strong physiological arousal. Such situations include:

Pain, threats, and vulnerability (BDSM and related);
Disgust-triggers (urine / scat);
Being touched in certain vulnerable areas of the body like the feet and the front of the neck (foot fetishes and related).

How do I know that the feet and neck are “vulnerable”? Because I am an expert in hand-to-hand combat. Haha, just kidding. Because these are areas where people are sensitive, and ticklish, and where they tend to execute innate defensive reflexes upon being touched.

See A Theory of Laughter §4.1 for more details on why and how all the above trigger physiological arousal, including the connection to tickling.

6.6 The Lisa Feldman Barrett flu anecdote

Back when I was in graduate school, a guy in my psychology program asked me out on a date. I didn’t know him very well and was reluctant to go because, honestly, I wasn’t particularly attracted to him, but I had been cooped up too long in the lab that day, so I agreed. As we sat together in a coffee shop, to my surprise, I felt my face flush several times as we spoke. My stomach fluttered and I started having trouble concentrating. Okay, I realized, I was wrong. I am clearly attracted to him. We parted an hour later—after I agreed to go out with him again—and I headed home, intrigued. I walked into my apartment, dropped my keys on the floor, threw up, and spent the next seven days in bed with the flu. —How Emotions Are Made (Lisa Feldman Barrett, 2017)

From my perspective (not Lisa Feldman Barrett’s^[12]), this anecdote seems like crystal-clear evidence of my central claim: there are hypothalamus / brainstem innate reaction circuits whose direction of causality is not only sexual attraction → physiological arousal, but also physiological arousal → sexual attraction.

(Possible objection: “Wouldn’t this anecdote involve tonic, not phasic, physiological arousal?” Nope, I think it’s phasic, thanks to coincidental timing. I propose that, as Dr. Barrett’s body was starting to react to the flu, it created lots of spikes of physiological arousal at random intervals, and some of those spikes happened to come at moments when she was paying attention to the guy. I stand by my belief that the physiological arousal has to be phasic, and in sync with thoughts about a particular person, to cause sexual attraction; I don’t think tonic physiological arousal does the job. If a woman is generally excited, e.g. she’s excited about an upcoming first day on the job, I don’t think she’ll get globally more sexually attracted to everyone, the way men do when they’re horny. Right? Well, someone can correct me if I’m wrong.^[13])

6.7 Heterosexuality?

Well, men do tend to be taller… 🤔

7. Conclusion

Like I said at the top, I’m very interested in thoughts and feedback! …Especially (but not exclusively) from the many allistic cis women who regularly read my work. Ha ha ha.

Thanks Towards_Keeperhood & Linda Linsefors for critical comments on earlier drafts.

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How the Mind Works (Steven Pinker, 1997) Chapter 7: “…In foraging cultures, everyone agrees that some people are sexier than others, and the sexpots are usually young women and prestigious men. Yanomamo men, for example, say that the most desirable women are moho dudei, an expression that when applied to fruit means perfectly ripe and when applied to women means between fifteen and seventeen years old. When shown slides, Western observers of both sexes agree with the Yanomamo men that the moho dudei women are the most attractive. In our society, the best predictor of a man's wealth is his wife's looks, and the best predictor of a woman's looks is her husband's wealth. Dumpy-looking cabinet secretaries like Henry Kissinger and John Tower are called sex symbols and womanizers. Octogenarian oil barons like J. Paul Getty and J. Howard Marshall marry women young enough to be their great-granddaughters, such as the model Anna Nicole Smith. Not-so-handsome rock stars like Billy Joel, Rod Stewart, Lyle Lovett, Rick Ocasek, Ringo Starr, and Bill Wyman marry gorgeous actresses and supermodels. But former Representative Patricia Schroeder says she has noticed that a middle-aged congresswoman does not radiate the same animal magnetism to the opposite sex that a middle-aged congressman does…”
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Not all animals! For example, coral polyps simply release their sperm or eggs into the water, where they float around, find each other, and fertilize. For my part, no thank you, I am very much happier with the human system, involving flirting, love, sex, childrearing, etc. I might have felt differently in high school.
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See How the Mind Works (Steven Pinker, 1997) Chapter 7 for a review of the evolutionary psychology of sexual attraction in humans. I don’t believe everything in that chapter, but I do think it’s mostly right in the big picture—happy to chat in the comments. All unsourced evo-psych claims in this post probably come from that book chapter.
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Elaborating on this point: In principle, an evo-psych explanation of why some behavior is adaptive is basically useless for the question of how, neuroscientifically, that behavior comes about. But in practice, there’s a strong overlap between “people who talk about evo-psych” and “people who subscribe to the so-called ‘evolved modularity’ school-of-thought in neuroscience”. That overlap leads to some conflation of the “why” and “how” questions. Let’s be clear: evo-psych and evolved modularity are separate. For my part, I strongly endorse many (not all) evo-psych claims, but also strongly reject almost every aspect of “evolved modularity”. For details see “My take on Jacob Cannell’s take on AGI safety” §1 and “Learning from scratch” in the brain.
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I think that §2 (“appearance-based sexual attraction”) will be the part that’s more centrally relevant for cis men (and most trans women) of all sexual orientations, whereas §3–§6 will be the part that’s more centrally relevant for cis women (and most trans men) of all sexual orientations. Again, it’s overlapping distributions in all cases.
(And there are other people too, who don’t fit in any of those categories, but I don’t know enough to comment further.)
I could be wrong about any of these points! For example, an earlier footnote noted that middle-aged congressmen do much better than middle-aged congresswomen on the heterosexual dating market. But what if the congresswoman is a lesbian? Does she have to constantly fight off suitors? (Sincere question, I have no idea.)
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See “Neuroscience of human social instincts: a sketch” §5.2 for more discussion of a putative friend / enemy parameter in the brain.
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The book chapter authors bring up a lot of ideas, most of which I tend to disagree with, happy to chat about that in the comments. (But first I would have to re-read it more carefully myself! I only skimmed it.) Anyway, regardless of their specific claims, the book chapter is a good starting point for learning what’s in the literature.
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It’s actually even more elegant than that: in How Do You Feel (2014), Bud Craig argues convincingly that somatosensory inputs are in fact a special case of interoceptive inputs! Specifically, he argues that (some of the) somatosensory nerves have much more in common with nerves carrying interoceptive input signals like “the sense of feeling angry”, than with nerves carrying exteroceptive inputs like vision. Conceptually, he suggests that the skin is an organ, and the sense-of-touch evolved first and foremost as a way to track the status of that organ to enable homeostatic feedback control.
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See Neuroscience of human social instincts: a sketch §5.3 for a bit more about phasic physiological arousal.
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Since everyone is instinctively eager to please tall people, especially tall men, no wonder they get promoted more! A neat example is how, in the business world, I think it’s well known that if you look at the CEO of a large company, you can confidently guess whether they founded the company, versus rose through the ranks, based on their height: founder-CEOs are close to population-average height, whereas people who got promoted up to CEO are super tall. I’m not sure if anyone has done a rigorous systematic study to back that up, but some examples (from here, the author claims not to have cherry-picked) are: John S. Watson (promoted up to CEO of Chevron): 6’4” = 193 cm; Tim Cook (promoted up to CEO of Apple): 6’3” = 190 cm; Jeffrey Immelt (promoted up to CEO of General Electric): 6’4” = 193 cm; Mark Zuckerberg (founded Facebook): 5’9” = 175 cm; Larry Page (co-founded Google): 5’11” = 180 cm; Sergey Brin (co-founded Google): 5’8” = 173 cm; Jack Dorsey (co-founded Twitter): 5’11” = 180 cm; Richard Branson (founded Virgin): 5’11” = 180 cm; Elon Musk (quasi-founded Tesla, PayPal, SpaceX): 5’11” = 180 cm; Warren Buffett (quasi-founded Berkshire Hathaway): 5’10” = 178 cm.
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Just to spell it out: I think there are “sexual attraction circuits” that lead to feeling sexually attracted towards a particular person, and those circuits are the subject of this post. And if those circuits are more active during sex, towards the partner, then that will obviously contribute to feeling more horny and enjoying sex more.
In principle, a sexual fetish could either work through those circuits (making them more active) or independently of those circuits (as a separate contributor to feeling horny and enjoying sex). I don’t have a strong opinion about which of those is the case. Also, it might be different for different fetishes, and it might be different for the average man vs woman.
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In the book, she explains the anecdote in a different way, basically as an example of misattribution of arousal. I don’t buy her explanation—see Lisa Feldman Barrett versus Paul Ekman on facial expressions & basic emotions and Why I’m not into the Free Energy Principle. (I’m more broadly skeptical of pretty much everything in the “misattribution of arousal” literature, although it has kernels of truth.) So for this post, I’m ignoring her explanation and just talking about the anecdote by itself.
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Sketchy anecdotal counterexample: An anonymous reddit account claims here that she feels sexually aroused from the feelings of shock and surprise associated with a “rush after near/almost incidents”. But that’s just one person (if it’s even a real person), and a friend commented that this didn’t really ring true for her.