Saturday, December 15, 2007

Pedal to the metal

The last few days have seen quite a flurry of attention to the issues of genes and evolutionary change, issues with great relevance for providing at least some answer to the question of 'who we are'.

This struck me first on Tuesday, while I was perusing a copy of the Times that someone had abandoned in the Eurostar. Strikingly titled 'Why the human race is growing apart', it quotes one of the researchers:

“Human races are evolving away from each other,” said Henry Harpending, Professor of Anthropology at the University of Utah, who led the study.

“Genes are evolving fast in Europe, Asia and Africa, but almost all of these are unique to their continent of origin. We are getting less alike, not merging into a single, mixed humanity.

“Our study denies the widely held assumption that modern humans appeared 40,000 years ago, have not changed since and that we are all pretty much the same. We aren’t the same as people even 1,000 or 2,000 years ago.”

Hmm, I thought.

Having spent a fair amount of effort trying to come to grips with the connections among evolution, psychology and history, this gave me much to think about. This is particularly so as I have been largely convinced by the argument of evolutionary psychologists that human nature -- while not completely unchanged in the last dozen millennia -- remains shared enough to speak of the 'psychic unity' of Homo sapiens.

(I discussed this in an article published earlier this year. There were two responses -- by Martin J. Wiener and Barbara H. Rosenwein -- to that essay, and they, along with my response-to-the-responses has just appeared in Cultural and Social History.)

In any case, over the next couple of days, I received a few helpful e-mails from friends who know about my interest in such things, pointing me to other stories on the study. One of them came from a fellow historian who has become quite enthusiastic about the notion of 'recent' biological change influencing behaviour. He sent me a link to the Los Angeles Times report on the study, which opens:

The pace of human evolution has been increasing at a stunning rate since our ancestors began spreading through Europe, Asia and Africa 40,000 years ago, quickening to 100 times historical levels after agriculture became widespread, according to a study published today.
Hmm, I thought again, sitting in a London internet café and having relatively little time to do any follow-up.

I finally had a chance today to examine another story on the study, in the New York Times.

It opens with this...

The finding contradicts a widely held assumption that human evolution came to a halt 10,000 years ago or even 50,000 years ago. Some evolutionary psychologists, for example, assume that the mind has not evolved since the Ice Age ended 10,000 years ago.
...which is a rather curious statement, since I can't think of any reputable biologically-aware researcher in any field who thought that 'human evolution came to a halt' at some point in the past.

The argument evolutionary psychologists make tends to be one that -- while there has undoubtedly been 'recent' genetic change (lactose tolerance and disease resistance being prime examples) -- the relative influence of these changes compared to those during the much longer Pleistocene is probably minimal.

The breathless quality of the reporting on this is also somewhat odd, as the 'acceleration' doesn't seem all that surprising: since human populations became significantly larger, there will be more mutations on which natural selection can operate; as human populations were also inhabiting more diverse environments, this could have subjected some populations to new selective pressures. As the LA Times piece notes,

the research team was able to conclude that infectious diseases and the introduction of new foods were the primary reasons that some genes swept through populations with such speed.
I might be missing something, but even my non-expert understanding of evolution would lead me to expect exactly this result.

So, in some way, I'm not so sure what the fuss is about.

But while it is clear that different environments' variations (in plant-life, sunlight, disease prevalence) might lead quite directly to 'rapid' change (remember, we're still talking vast amounts of time here), it is not clear to me why psychological change would be quite so rapid. The key 'environment' in terms of psychologically-relevant genetic change would be other people, and, by and large, it seems that on this point, the differences among different regional populations would not necessarily push human development consistently enough in one direction or another.

Most of the articles I've seen on the 'accelerating evolution' issue haven't really discussed a psychological angle on this, but it certainly is lurking there, particularly in the wake of James Watson's comments regarding intelligence and Africa. Harpending, moreover, was also co-author of a study claiming a recently-acquired genetic basis for high levels of intelligence among Ashkenazi Jews.

The New York Times raises cautions that some other articles missed in their apparent enthusiasm to proclaim significant genetic change in recent historical eras:

David Reich, a population geneticist at the Harvard Medical School, said the new report was “a very interesting and exciting hypothesis” but that the authors had not ruled out other explanations of the data. The power of their test for selected genes falls off in looking both at more ancient and more recent events, he said, so the overall picture might not be correct.

Similar reservations were expressed by Jonathan Pritchard, a population geneticist at the University of Chicago.

“My feeling is that they haven’t been cautious enough,” he said. “This paper will probably stimulate others to study this question.”

As it should. But as the NYT piece also points out, the methodology used cannot firmly establish what happened in the last 10,000 years or so.

The high rate of selection has probably continued to the present day, Dr. Moyzis said, but current data are not adequate to pick up recent selection.

(This point is also made by the graph included with the article.) Which makes all of the speculation about changes within the last thousand years or so a bit more...well, speculative than they sounded in the other articles.

This whole discussion inspired me to revisit Gregory Clark's argument in A Farewell to Alms, which I commented upon at length a while ago. (Part one. Part two.)

One of Clark's key arguments (simplifying somewhat) suggests (though rather vaguely) that rapid economic development in England in the early modern period was significantly influenced by genetic predispositions toward bourgeois values that were transmitted through English society by the fact that the wealthy out-bred the poor.

Via Clark's website, I found a couple of very readable critiques of his work. (There are a wide range of opinions on his work on offer there, and Clark deserves some credit for bringing them together. Of course, no publicity is bad publicity...)

In 'The Son Also Rises' (pdf) at Evolutionary Psychology Laura Betzig points out the weakness in Clark's argument that enhanced reproductive success by wealthy English led to an economic advantage due to the spread of middle-class values. First, the English rich were far from unique in this regard:
Clark knows that civilization began thousands of years ago, somewhere around Babylon; and he devotes a full chapter to the question, “Why England? Why not China, India, or Japan?” Why weren’t the Near East and Far East the best candidates for the natural selection of a hard-working middle-class? Because, he says, civilization in and around Babylon was more “unstable” than in Britain; and because in China and Japan—it pains me even to type these words—“the demographic system in both these societies gave less reproductive advantage to the wealthy than in England.” Clark cites evidence that Qing emperors fathered only as many children as average Englishmen living at around the same time (pp. 89, 209, 271, Figure 13.4). But of course for Qing emperors, as for any other emperors, legitimate fertility was low: Chinese emperors, like Assyrian emperors, like all other emperors got heirs on just one empress at a time, their legitimate wives; but they got bastards on scores, or hundreds, of consorts. Who should have transmitted, if not the high ethical standards of their bastards’ fathers, at least their hard-working genes. So much for the evidence in A Farewell to Alms.
Wealth, status and reproductive success may -- unsurprisingly -- correlate, but the extent to which the 'values' associated with that success can be passed on genetically is another matter, as Betzig points out:

There are other gaps in the logic. I am aware of dozens of studies that show a relationship between reproductive success and wealth or rank...; but I’m aware of no study that shows a correlation between reproductive success and the “middle-class values” of patience, nonviolence, literacy, thoughtfulness, or hard work.

And, it goes without saying, for those values to provide any benefit, they have to be possessed in a society that rewards them, turning us to various 'institutional' factors (from cultural assumptions, religious beliefs, social organisation, political structures, etc.) that Clark so blithely dismisses.

It is also worth pointing out that even in relatively recent history, those 'values' have not been the only routes to success. As I commented before on an earlier paper by Clark, concerning the period 1250-1800 with regard to the available means of getting ahead in life:

One might be granted a peerage, for instance, for reasons that had little to do with capitalist success and rather more to do with simply being on the right side of a political squabble, making a good marriage or having success in war. (Just as losing one's wealth might have had to do with contingencies related to the above factors.)

'Wealth' and 'success' were being amassed in England in a variety of ways: slave trading, tobacco planting, empire building, monarch-bribing, textile weaving and goods trading (not to mention, at least in the earlier period, being good with a sword).

Which gene is it, precisely, that is going to promote success in all these different ways of getting ahead in life?
In her detailed critique of A Farewell to Alms, Dierdre McCloskey, I see, makes a similar observation. She divides Clark's argument into various elements and 'links', and as part of that discussion notes:

In light of Clark’s methodological convictions...the most embarrassing broken link is A, between “Rich breed more” and “Rich people’s values spread.” Nowhere in the book does Clark calculate what higher breeding rates could have accomplished by way of rhetorical change. It could easily be done, at any rate under his mechanical assumption about how the social construction of values works. Clark assumes that the children of rich people are by that fact carriers of the sort of bourgeois values that make for an Industrial Revolution.

To be sure, this is an odd characterization of the medieval or early modern relatively rich. A rich bourgeois of London in 1400 devoted most of his effort to arranging special protection for his wool-trading monopoly. His younger sons might well have taken away the lesson, repeated again and again down to Elizabethan England and Lou Dobbs, that it’s a good idea to regulate everything you can, and quite a bad thing to let people freely make the deals they wish to make. And a Brave Sir Botany who had stolen his riches, say, or was a successful courtier who had received them from Henry VIII dissolving monasteries, say, would not automatically, one would think, transmit sober bourgeois values to younger sons. A society that extravagantly admired aristocratic or Christian virtues could corrupt even a Medici banker into thinking of himself as quite the lord and yet also a godly son of the Church. In a similar way nowadays an extravagant admiration for the neo-aristocratic values of the clerisy corrupts the bourgeois daughter into scorning her father’s bourgeois occupation.
McCloskey's critique is worth reading, even if it's flawed. (She doesn't seem to know what a 'meme' is, for example: she sees Clark as promoting a 'meme' theory, but memetics actually tends to separate biological and cultural development. Also, she curiously lumps Clark in with Steven Pinker whose arguments tend to be both much better and much different than Clark's.)

To be honest, I'm not really sure what to make of all this. It's not my field, and I'm in the position of anyone who wants to make use of the insights from another field: you can educate yourself on it to the extent that your time and interest allows, but in the end, you depend on particular experts who are able to translate those findings in a language that is generally comprehensible. Unfortunately, those experts always seem to be at war with other experts in their fields.

But language and the history of human behaviour are two things I know a little bit about, which is perhaps why I don't like so much the leap from the molecular level to vast statements about how 'human races' are 'evolving away from one another'. (In particular when they get picked up in the press, where they are presented far less carefully than they should be.)

What does this mean? How relevant are these differences to determining what makes us human?

I have the sense that the overwhelming amount of what we share is being drowned out in the emphasis to focus on difference, as interesting as those might be. Both perspectives are not, of course inherently mutually exclusive: evolutionary psychology's emphasis on a common human nature would seem to admit some variation, and the differences found by population genetics are only meaningful in relation to that commonality.

At a certain level of specificity, the genetic differences seem vast, but step back a bit and they're relatively less so. People in different regions might tend to have different levels of disease resistance, say, but their immune systems all work the same way. Which of these observations is more important in understanding what makes us human? I would say the latter (while admitting that understanding the former is important for many reasons).

When Harpending (quoted above) says that 'we' are 'not the same' as people even 1,000 years ago, what does that mean? I am, for instance, not the same as you (whoever you -- dear reader -- might be). But that appears to be a pretty meaningless statement on the face of it. Were people 1,000 years ago different in any fundamental way than today? If so, what? It seems rather premature to make claims like that based only on counting changes in particular allelles without actually knowing -- in nearly all those cases -- what effect those changes have (on, for instance, behaviour).

But perhaps more significantly, it's unfortunate to see what could be a subtle and complex synthesis of different perspectives and levels of analysis of our humanness (shared across many fields) being shunted aside by a set of competing one-dimensional, either-or answers to why things work the way they do: institutions vs. genes, materialism vs. culturalism, similarity vs. difference, universality vs. particularity.

Maybe this is because academic work is partly driven by the very normal (indeed, human) cravings for attention and status (and maybe our innate tendency toward tribalism) which seem to affect every other human enterprise

I just don't think that's necessary a good thing.


A draft of the original paper (which is very technical) is available here.

Discussion and criticism of the article (also quite technical) can be found at Gene Expression.

There is also a long article from the Economist on the study is also freely available.


Sharon said...

The Guardian also has a take on the 'humans evolving faster' story:

J. Carter Wood said...

Thanks, Sharon, I hadn't seen that one.