[Content note: Discussion of debate over gay marriage]

[Epistemic status: Very preliminary. Probably missing something. Looking forward to hearing what.]

The term “cultural evolution” is getting used a lot nowadays. In its simplest form, it just means cultures preserve useful ideas and tips. For example, as per Carcinization:

[The Lost European Explorer] experiment has been repeated many times when European explorers were stranded in an unfamiliar habitat. Despite desperate efforts and ample learning time, these hardy men and women suffered or died because they lacked crucial information about how to adapt to the habitat. The Franklin Expedition of 1846 illustrates this point. Sir John Franklin, a Fellow of the Royal Society and an experienced Arctic traveler, set out to find the Northwest Passage, and spent two ice-bound winters in the Arctic, the second on King William Island. Everyone eventually perished from starvation and scurvy. The Central Inuit have lived around King William Island for at least 700 years. This area is rich in animal resources. Nonetheless, the British explorers starved because they did not have the necessary local knowledge, and despite being endowed with the same cognitive abilities as the Inuit, and having two years to use these abilities, failed to learn the skills necessary to subsist in this habitat.

Presumably, the Inuit neither conducted deliberate centralized experiments to determine what food in their area was edible, nor derived the information from explicit understanding of the principles of nutrition. Rather, over thousands of years, various proposals like “eat those yummy-looking red berries that grow on the small bushes” and “always hunt seals in large groups” were accidentally tested, with the successful ones spreading until they became universal tradition and the disastrous ones being warned against as taboo. Without any deliberate effort, the Inuit ended out with a remarkably effective set of survival techniques.

Something like this seems so obviously true as to not require further discussion.

However, recently “cultural evolution” has slipped, without much consideration, into a much stronger meaning. For example, in his commentary on Ross Douthat’s article on gay marriage, Tumblr user severnayazemlya writes:

What Douthat is saying is that there was some system that existed sometime in the past that was more human-shaped than Marcotte’s vision for the future. Gavin McInnes has said the same. The conservative argument is that the cultural inheritance that the past hands down to the present is more human-shaped than most reforms proposed in the present – because there were reformers in the past, and, absent major breaks in the continuity, past reforms have had time to be tested for their fit: those that worked were kept, and those that didn’t were discarded.

Likewise, on one of my recent blog posts, commenter Steve Johnson writes:

Every surviving cultural tradition on Earth is hostile to homosexuality – that’s no accident. That’s cultural evolution in action.

This form of cultural evolution seems to work something like so: our culture, and indeed most cultures, used to have a certain conception of marriage. That conception of marriage outcompeted other conceptions of marriage from the distant past all the way to the present. Societies with alternative conceptions of marriage seem to have died out. That suggests that this conception contains something useful; even if we can’t see it we should be wary of interfering with it, in the same way we are wary to disrupt our body’s metabolic balance or alter genes willy-nilly.

The difference between the obvious Inuit form of cultural evolution and the non-obvious marriage form is that of within-culture versus between-cultures evolution.

Consider: one Inuit tries the red berries and discovers they make her sick. Out of pure self-interest, she decides not to eat them again, and tells her friends the same. Also out of self-interest, they decide not to eat them; those who think they can get away with eating them anyway are quickly disabused of the notion. The taboo against eating red berries quickly spreads throughout the culture.

Marriage doesn’t seem to work that way. If one person decides not to marry in the usual way, it doesn’t necessarily hurt that person. They might have lots of affairs, and enjoy them. Or they might get gay married, and enjoy that. Any claim that cultural evolution argues against gay marriage because it’s bad for the actual gay-married person must face the fact that actually gay-married people seem totally okay with it, and in fact are urging their friends to do it, the exact opposite of the red berry situation.

So I interpret it as a different claim: a culture that allows gay marriage will, for various reasons, become weak and unsuccessful. Then it will be crushed by other cultures, either militarily, economically, or in a sort of marketplace of ideas where people convert to or assimilate into the other culture because it’s more attractive and successful.

Note that THIS IS REALLY DIFFERENT FROM THE FIRST TYPE OF CULTURAL EVOLUTION. In fact, it might be diametrically opposite. For example, gay sex may be lots of fun – and as people figure this out and tell their friends, it will be positively selected through the first type of cultural evolution. But it might weaken a culture’s Moral Fabric – in which case it will be negatively selected through the second type of cultural evolution.

This is sort of group selectionism, but in this case I’m okay with it. Consider the analogy of a cancer cell. Becoming cancerous makes a cell much more likely to spread within its organism – the equivalent of positive intracultural selection – but also makes its organism at a severe disadvantage compared to other organisms – the equivalent of negative intercultural selection. As a result, we expect organisms to evolve strong internal defenses against cancer – which in fact they have. In the same way, it’s plausible that cultures might evolve strong internal defenses against actions that are fun but Weaken Moral Fabric, and sure enough we find that everything halfway enjoyable comes with a lecture from our elders about Why We Shouldn’t Do It. Presumably if these things really Weaken Moral Fabric in an important way, then those cultures that develop strong internal defenses against them – for example, a strong and well-enforced religious taboo against gay marriage – will be more likely succeed while other cultures die out.

So in principle this kind of intercultural selection could happen. In practice I think the effect is negligible.

Evolutionary biology has a lot of equations to calculate how long it will take a positively-selected trait to spread. It depends on a lot of different things, but the most salient here are the length of a generation for the affected organism, and the extent of the selective advantage conferred by the trait.

How long is a “generation” in cultural evolution? Rome lasted a thousand years, Byzantium another thousand. It took about three hundred years for Christianity to replace paganism in Rome; Enlightenment values have been replacing Christianity for three hundred years already and aren’t nearly done. Any sort of evolutionary process that involves waiting for Rome to fall is a process that will take way longer than human history to come to any sort of conclusion.

How much advantage can an individual cultural trait confer? Probably very small in the grand scheme of things. Compare Judeo-Christian attitudes about sex to Greco-Roman attitudes about sex. One might argue that the Judeo-Christian attitudes are superior, since Christianity did eventually take over Rome. On the other hand, both Greece and Rome took over Israel at various points; various Jewish texts record that during that time a lot of Jews were defecting to Greco-Roman culture and there were precious few defections the other way. It would seem that all of the other differences between Greco-Roman and Judeo-Christian culture – theology, non-sexual mores, geography, technology, philosophy – had a lot more effect than the sexual mores.

This is also unsurprising from a population biology perspective. Suppose that one of my children gets a mutation causing 1% less risk of infectious disease. This is fine, but they might get killed in a car accident before their tenth birthday, or be too ugly to find a partner, or get an infectious disease anyway because 1% less risk isn’t really much less risk. If my child survives, and passes her mutation on to millions of other people all with their randomly distributed level of other good and bad genes and good and bad luck, then maybe eventually over thousands of generations, people with the new beneficial mutation will take over from people without it.

But, as mentioned above, we don’t have thousands of generations for cultural evolution to do anything. Communism, which basically took all of the worst ideas in history, combined them together into a package deal, and said “Let’s do all of these at once”, took almost a century to collapse, and still hasn’t collapsed in a couple of places. Imagine if instead of Communism happening, twenty different countries had adopted one Communist ideal each and we’d waited to see which ones grew and which ones declined. We’d still be waiting, and probably instead of getting any useful information we’d just end up seeing the Rise of China and not being sure whether it was because of their Communist ideal or something else.

The closest thing I can think of to anyone actually gaining useful information out of cultural evolution is the failure of various small communes and social experiments. But once again, these only failed because they tried all the bad ideas at once, and a big part of their failure was intracultural evolution – the people involved noticed they, personally, were poor and unhappy, said “screw this”, and went back to non-communal living.

So overall, I think any appeal to intercultural evolution as having proven anything is on very shaky ground. Appeal to intracultural evolution is much more reasonable, but crucially, can’t be used to override people’s own decisions about whether they’re happy doing something or not. If someone says “I enjoy this, and I’ve been doing it a few years and not noticed any bad consequences, and I suggest you do it as well”, then you’re going to have a hard time arguing against the practice on grounds of cultural evolution.

[EDIT: Actually, this leaves out a possible third kind of cultural evolution, where cultures try good ideas, learn to like them, and stick with them; or try bad ideas, learn to hate them, and stop. For example, China experimented with Maoism, that didn’t work, then experimented with a variant of capitalism and liked it enough to stick with it thus far. Given that something similar is happening on smaller scales (eg experimentation in policing, education, budgeting, etc) all the time, you could eventually end up with a pretty finely-tuned culture. This obviously happens, but it seems loaded to think of this as ‘cultural evolution’ instead of just ‘guess and check’ or ‘learn from history’. The former formulation suggests something illegible to understanding; the latter formulation suggests that it happens by deliberate human responses to bad consequences, and makes it less of an excuse for general conservativism.

If you say “Let’s be Maoist!” I can say “No, the Chinese tried that, it led to X, Y, and Z consequences, and then they switched to something else and things got better.” The cultural evolution argument for traditional sexuality seems to be trying to argue in the absence of, or in parallel to, such observable historical lessons.

Likewise, there’s a cultural evolution argument that we tried traditional sexuality, that made a lot of people unhappy, and now we’re trying something else. It’s unclear how this is different from the Maoism example in a way that makes jettisoning Maoism good, but jettisoning traditional sexuality bad.]