From the Dynomight blog: You, Your Parents, And The Hotness Of Who You Marry.

They start with a traditional situation: some romance novel heroine wants to marry a tall, dark stranger. But her parents want her to marry a much older nobleman/doctor/engineer who can provide her with a stable income. Or the gender-flipped version: the young man courts a beautiful debutante, while his parents try to force him to marry the plain-faced daughter of their business partner.

Evolutionary psychology has pat explanations for both sides here. People want attractive partners because attraction correlates with health, fertility, and status (eg the debutante’s wide hips and large breasts mean she’ll be able to give birth and nurse effectively; the stranger’s height means he must be strong and healthy). But people also want wealthy partners from good families, because they’ll be able to give more resources to the children.

Dynomight’s question is: why do the suitors and the parents disagree here? Everyone involved (evolutionarily) wants the same thing: lots of healthy, successful descendants. Sexual attractiveness and financial resources both contribute to that some amount, but suitors and parents shouldn’t differ on the relative importance of each? So why is it traditionally the suitors who care about attractiveness and the parents who care about resources?

(yes, most people care a little about both - there are gold-digging suitors and parents who are proud of their son/daughter-in-laws’ good looks - but the trend for parents to care relatively more about wealth and good breeding seems clear, and Dynomight cites research showing this is true)

Dynomight mentions a kind of boring theory: parents are older and wiser than suitors, and so less hormonally obsessed with attractiveness. I don’t think this really works: we’re asking this question on the evolutionary level, so this just passes the buck: why did evolution give older people a less attractiveness-seeking hormone profile?

But they also mention a much more clever theory, dating back to Robert Trivers:

Your parents share an equal number of genes with all their grandchildren. But you share twice as many genes with your kids as with your nieces and nephews. If you marry a doctor, maybe they’ll help your niece with tuition or convince her to major in pre-med instead of comparative Sanskrit opera studies. But if you marry someone with amazing genes, your niece will get none of them. So maybe your parents care more about the social status of who you marry because that has benefits for all their grandchildren. You care more about attractiveness because you give twice as much weight to your own kids.

They do some math and it doesn’t quite work out, but they have some good arguments for why maybe this is true on the margin and then the math does work.

I find neither of these theories convincing.

One objection to the latter (h/t AM): what if you’re an only child? Then your parents don’t have to consider the impact of your mate on your siblings and their children, and your interests should be aligned. But only children seem to have the same disagreements with their parents about mate choice as everyone else.

Maybe evolutionary imperatives aren’t fine-grained enough to tell parents to act one way if they have only one child, and another way if they have many children? That seems like a hard sell if you’re first claiming they are fine-grained enough to tell parents to act one way, and children another. You would have to land within a pretty narrow range of how fine-grained evolutionary imperatives can be. If you’re going to question how fine-grained evolutionary imperatives can get, why not go a little further and get rid of the entire problem?


There’s an old rationalist saying: individuals are best thought of as adaptation-executors, not fitness-maximizers.

The idea is the same one that I was trying to get across in the mesa-optimizers post, when I wrote:

Consider evolution, optimizing the fitness of animals. For a long time, it did so very mechanically, inserting behaviors like “use this cell to detect light, then grow toward the light” or “if something has a red dot on its back, it might be a female of your species, you should mate with it”. As animals became more complicated, they started to do some of the work themselves. Evolution gave them drives, like hunger and lust, and the animals figured out ways to achieve those drives in their current situation. Evolution didn’t mechanically instill the behavior of opening my fridge and eating a Swiss Cheese slice. It instilled the hunger drive, and I figured out that the best way to satisfy it was to open my fridge and eat cheese.

Urges like “mate with anything that has a red dot on it” are adaptations. Animals can execute them as simple programs.

The opposite of that would be just giving the animal an urge towards maximizing its inclusive genetic fitness, and a big enough brain to figure out what that means. Imagine eg a human with a driving goal to have as many children as possible, who’s capable of thinking of things like donating lots of sperm to sperm banks. This is honestly the winning move in the evolutionary game, but humans haven’t been smart enough for long enough for evolution to instill something like this in us. Instead we get somewhere between half-hearted approximations of this kind of thing, and blind adaptation-execution programs.

A simple example of this is Ondine’s Curse, a rare disease (usually caused by a tumor) where the breathing-related parts of someone’s brain stop working. A patient may notice that they no longer have any desire to breathe. They may think “Well, that’s weird, but seems like I probably still need oxygen to live, I’m going to breathe anyway.” Lacking any natural sense of when to inhale/exhale/stop, they hopefully calculate out what the right amount of breathing to do is for each breath manually. Unfortunately, these people usually die when they fall asleep and can no longer reason themselves into breathing. But their sacrifice serves as a useful example of adaptation-executors vs. fitness-maximizers. A healthy person, breathing because their body instinctively demands oxygen, is executing an adaptation. A Curse patient, breathing because they have a goal of continuing to be alive, and they understand rationally that obtaining oxygen is a subgoal, is maximizing fitness.

You can have as many layers as you want. A very adaptation-execute-y hunger drive might be “see shiny red berry, mmmm, looks so good, grab and eat”. Somewhere in the middle might be “feel stomach pangs, go to fridge, get a snack”. More towards the fitness-maximizer end might be “realize that nutrition is important for avoiding deadly heart attacks, read recommendations, eat a balanced diet.”


Here’s a paper on mate choice in nonhuman primates. Suitors place surprisingly little emphasis on mates’ appearance, but there is some evidence that they do consider body size. They also consider a potential mate’s position in the dominance hierarchy. So even here, we have our two categories of positive traits: attractiveness and status. On the other hand, there’s no evidence at all that these animals’ parents play much of a role.

So: suitors’ mate choice depends on innate, evolutionarily well-established software. Parents’ mate choice depends on - well, it’s not clear. I tend to think that a few million years between primates without parental mate choice and the current day might not be enough time to give people really good innate parental mate-choice instincts.

So suitors’ mate-choice instincts are probably very finely-honed, specific drives and instincts. There’s some deep animal if-then statement saying that if someone has a youthful-looking face, they’re probably healthy and fertile and you should be more willing to mate with them.

Parents are probably going off of something like a vague desire that their children and grandchildren do well, without any supporting software. That means they have to use their reason to figure out how this cashes out in the real world.

Which is better: built-in micro-managing instincts, or human reason? Depends on the situation. Our built-in nutrition instincts are amazing in lots of ways: people with hyponatremia will feel a craving for salt, even if they have no idea what hyponatremia is or why salt should solve it; in order to replicate that with human reason you’d need an MD and lots of expensive laboratory equipment. On the other hand, our built-in nutrition instincts are also what tells us to take a fifth donut after we’ve already eaten four, which even a moron can use their reason to figure out isn’t a good idea. So it can go either way.

Somebody using their built-in mate-choice instincts can figure out lots of things that would otherwise take a bunch of obstetricians and geneticists to tell them. But also, they’re kind of at risk of running off with some floozy who will turn out to be addicted to drugs and not a very good parent for their children.

Someone using human reason to figure out mate choice is going to be biased towards the human-comprehensible concepts that they use all the time - things like status hierarchies and money. An average Indian mother isn’t going to know about which physical features predict healthy pregnancies or which very minor skin imperfections signal poor immune function, but she is going to know that potential son-in-law X makes $20,000 a year more than potential son-in-law Y.

I think this is why suitors and parents have systematically different preferences about who to marry. It’s the same reason why I might be tempted to overeat at the ice cream shop, but my parents can easily tell me “you should watch your weight” (while facing their own temptations themselves). It’s the same reason why heroin addicts have trouble coming clean, but their parents have no trouble lecturing them about it. It’s the same reason why porn sites have lots of material about people copulating with high-quality mates, but none about people finding high-quality mates for their children. “POV: WATCH YOUR DAUGHTER MARRY RICH DOCTOR”. Evolutionarily it makes sense, but the urge isn’t implemented on that level.


In the mesa-optimizers post, I wrote:

Mesa-optimizers would have an objective which is closely correlated with their base optimizer, but it might not be perfectly correlated. The classic example, again, is evolution. Evolution “wants” us to reproduce and pass on our genes. But my sex drive is just that: a sex drive. In the ancestral environment, where there was no porn or contraceptives, sex was a reliable proxy for reproduction; there was no reason for evolution to make me mesa-optimize for anything other than “have sex”. Now in the modern world, evolution’s proxy seems myopic - sex is a poor proxy for reproduction. I know this and I am pretty smart and that doesn’t matter. That is, just because I’m smart enough to know that evolution gave me a sex drive so I would reproduce - and not so I would have protected sex with somebody on the Pill - doesn’t mean I immediately change to wanting to reproduce instead. Evolution got one chance to set my value function when it created me, and if it screwed up that one chance, it’s screwed. I’m out of its control, doing my own thing.

[But] I feel compelled to admit that I do want to have kids. How awkward is that for this argument? I think not very - I don’t want to, eg, donate to hundreds of sperm banks to ensure that my genes are as heavily-represented in the next generation as possible. I just want kids because I like kids and feel some vague moral obligations around them. These might be different proxy objective evolution gave me, maybe a little more robust, but not fundamentally different from the sex one.

Since then, I’ve been thinking about this a lot. Is it correct to model myself as having (let’s call it) a reptile-level instinct of “genital friction feels good”, plus a separate mammal-level goal of “kids are cute”, while missing a human-level goal of “maximize inclusive genetic fitness, eg by donating to sperm banks”? Where by “reptile-level” I mean “evolution implemented this on reptile-level cognitive machinery” and by “mammal-level” I mean “and then once mammals evolved with more complex cognitive machinery, evolution went back and implemented the same goal at a different level”?

(I don’t want to make actual claims that reptile vs. mammal cognition is the exact distinction here, just trying to vaguely gesture at the idea of different evolutionary levels of representing the same idea)

Or what would be the alternative? Maybe the genital friction one is the “real” evolutionary incentive to reproduce, and “kids are cute” is a byproduct of some other drive, like the drive to protect children once you have them, but as a spandrel this also makes you want to have children? And we’re sure lucky it does, because otherwise we would have gone extinct as soon as we invented condoms?”

Or is the desire to have children (separate from the desire to have sex) cultural? We notice other people having children (maybe because they were born before the era of birth control) and saying nice things about the process, and this makes us feel like we should have children too? Certainly some people say they only have children because they feel social pressure to do so. Maybe that’s the whole game.

What would it mean to have separate reptile, mammal, and human drives? If some man has a fetish for, let’s say, tall Asian women wearing red bikinis, this can’t be because evolution encoded a preference for this particular type in his genes. And it’s probably not because, using his human reason, he decided that tall Asian women wearing red bikinis were the best way to achieve his goals. It has to be the signature of a drive compressed enough to make sense in reptilian logic trying to unfold itself until it makes sense on the human level. Is there just one drive, which leaves different traces of itself on various levels as it tries to come into existence?

I find the suitors vs. parents conflict interesting as a test case. It certainly looks like the suitors are working off one level of drive, and the parents another, in a way suggesting they’re genuinely separate.