Happy Belated Birthday
I intended yesterday to write a review of Gregory Cochran and Henry Harpending’s book, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. It is a book that I heartily recommend – particularly to those who are not already inclined to sympathy with “genetic-deterministic” arguments, precisely because it is a very, very different sort of book from the sorts of books you might have read.
Darwin remains scandalous because the theory of evolution appears to threaten human distinction from the natural world (not to mention, of course, contradicting the literal accounts of creation). But the really scandalous thing about Darwin’s insight was not that he saw kinship between humans and other animals (plenty of others noticed that kinship), nor that he was a materialist (there were materialists all the way back to the ancient world), but that he articulated a simple mechanism by which evolution could take place, and that this mechanism was an exceedingly ugly one: natural selection.
People in Darwin’s own day tended to hear his arguments and think he was explaining how we evolved “up” from “lower” animals, and felt relatively reassured. But there is no “up” in evolution, except in two trivial senses: there is a directional arrow in evolution (later forms evolve from earlier ones), and there is the possibility of increased complexity over time, an apparent reversal of entropy (apparent because it is in fact underwritten by input of energy from the sun). On one level, we’re the “pinnacle” of evolution because we’re at the top of the food chain, are extremely numerous, are able to adapt to numerous environments, and are relatively late arrivals on the scene. But from another perspective, the “pinnacle” of evolution is the horseshoe crab, because it has survived largely unchanged for hundreds of millions of years. More to the point, the very things that we might point to as evidence of our “success” – large numbers, broad expansion across the planet – are precisely the characteristics of “weedy” species that we generally despise in the rest of creation. That fact in and of itself should give us pause in deriving any kind of transcendent value judgement from the workings of natural selection.
In any event, Darwin’s idea was simple and explosive, with repercussions that we are still assimilating. The deepest of these is the very conservative conclusion that victory in biological war is impossible. We cannot defeat disease, for example, merely hold it at bay, because our most successful efforts are precisely those that put selection pressure on microorganisms that will result in new diseases able to thwart our countermeasures. It remains to be seen whether we will be able to defeat our own weedy nature or whether we will ultimately return to the Mathusian world from which we only recently emerged. We may know a negative answer any time, but a positive answer we will never know for sure – certainly not until many generations have been born and given birth in our world of medically-controllable fertility.
So: what is special about Cochran and Harpending’s book is that it tackles human history – the period of the last 10,000 years – from a real Darwinian perspective. This is not a pre-Darwinian story of struggle – how “what did not kill us made us strong” – nor is it a series of “just so” evolutionary-psychology parables. Rather, it’s a story about how chance mutation can have massive historical consequences when that mutation turns out to be meaningfully adaptive.
There are really only a handful of very simple concepts at the heart of the various stories:
- Agriculture increased the overall size of the human population. More people = more mutations. Mutations are the building-blocks of evolution. Hence, with more mutations, all else being equal human evolution should have accelerated, not slowed, in the last 10,000 years.
- Not all individual human beings are equally well-adapted to all environments. But human beings in general are able to survive in a wide array of environments. Therefore, having spread to a variety of different environments, different groups of human beings have been subject to very different kinds of selection pressure by different environments. The fact of human adaptability doesn’t cut against arguments that human evolution has accelerated – our adaptability is a driver of accelerating evolution. And social environments are environments; they impose selection pressure just like any other environment.
- Adaptive mutations can spread with shocking speed precisely because they are adaptive. Relatively small differences in fertility – like relatively small differences in investment returns – compound quickly to massive advantages in population size.
None of these ideas should be especially controversial scientifically, but, like Darwin’s original dangerous idea, none are especially intuitive either. What Cochran and Harpending do with these ideas is explore various ways in which human history may have been shaped by evolution during historic time. This is why I say the book is very different from other books about sociobiology or a Darwinian view of human nature: those books tend to be focused on pre-history, about how human nature as it is today owes this or that to our primate ancestry, not on how we have changed, biologically, within the span of human history.
There are a great many fascinating digressions, but three big speculations stand out:
- That a meaningful genetic inheritance from our Neanderthal cousins materially contributed to the cognitive leaps forward that made possible art, language, agriculture, etc.
- That the development of lactose tolerance was the main driver of Indo-European expansion across much of Eurasia (and, subsequently, Bantu expansion in Africa).
- That high average Ashkenazi intelligence (as measured by IQ tests) is the result of selection pressure caused by the unique social niche of Jews in medieval northern Europe.
All of these are, as I said, speculations – in none of these cases do the authors present anything resembling the kind of evidence that would pass peer-review. Of course, that’s not the point of a book like this – their book is a work of popular science writing, and, as it should be, it is eminently readable and not at all too technical for the intelligent and reasonably informed lay reader. Anybody who could follow Guns, Germs and Steel or Before the Dawn can read this book with pleasure and interest. But precisely because it’s a work of popular science writing, it is somewhat problematic that so much of the subject matter is highly speculative. This is, generally, the kind of book you’d write to summarize developments in a particular discipline, and then conclude with some speculation about where the field might go next. But this field has only barely come into being, and the research needed to validate any one of the big-ticket hypotheses above would cross a number of disciplines and require years of work. Moreover, as Stephen Pinker pointed out in an article about the scholarly paper that formed the basis for the Ashkenazi IQ chapter, these sorts of hypotheses depend on getting a whole series of debatable points right – and they all have to be right for the hypothesis to work out. That makes validation much harder, but it also means that the odds are, pretty much by definition, long.
Which is all the more reason for more researchers to do work in this emerging field, and for scholars in different disciplines – population genetics, history, anthropology, linguistics, archaeology, etc. – to talk to one another. Darwin’s Origin of Species, after all, was written before anyone had any idea what could possibly cause the variation necessary for evolution by selection to occur. With nothing but Mendel to work with, Darwin’s own grand hypothesis was wildly speculative at the time. But had he not speculated as he did, other scientists would not have explored the then-uncharted territory that now we are beginning to map. I think the authors of The 10,000 Year Explosion would be very pleased if their work led to so much research on human evolution in historic time that every one of their speculative hypotheses was roundly refuted, because whatever we did discover would validate their questions, if not their answers.
In addition to Pinker’s article, Steve Sailer wrote a great post a while back on Cochran and Ashkenazi IQs.
Cochran is also (in)famous for his pathogenic theory of homosexuality, which, if nothing else, scores him points for intellectual courage (though he is in Utah).
And finally, if you want to read the National Academy of Sciences paper that spawned the book, here it is.
— JA · Feb 13, 09:47 PM · #
“it’s a story about how chance mutation can have massive historical consequences when that mutation turns out to be meaningfully adaptive.”
years ago greg stated this more pithily: selection is stochastic.
— razib · Feb 13, 10:12 PM · #
I happily purchased the book, even though Dr. Cochran once called me a f’ckin’ a**hole.
He’s probably right about that too.
;)
— matoko_chan · Feb 13, 10:16 PM · #
What’s the evidence for the claim about agriculture speeding human evolution? To my mind, it sits poorly with some facts about genetic change (not that the authors wouldn’t know those same facts..). It will be true that increased population sizes will speed up beneficial single gene mutations, but those are probably not the important ones (basically, if a random mutation in a single gene was beneficial, it probably would have already happened).
Probably more fitness enhancing changes come from interactions between multiple genes. If gene X is only beneficial in the presence of Gene Y, but substantially more detrimental without gene Y, then gene X has a low probability of spreading in a population where Gene Y doesn’t predominate. And as the population gets bigger, that probability decreases.
A heuristic argument for the above is that it’s well known that speciation primarily occurs in small isolated populations. It’s a heuristic because not all important beneficial mutations involve speciation.
— Justin · Feb 14, 03:33 AM · #
the possibility of increased complexity over time, an apparent reversal of entropy
Complexity, like entropy, is notoriously hard to define. And yet, I think Charles Bennett’s definition of complexity as ‘logical depth’ is the most intuitive and useful, and, happily, forces us to accept human society as the pinnacle of existence full stop.
Also, the horseshoe crab continues to exist at our pleasure. Insolence will not be tolerated.
— JA · Feb 14, 05:10 AM · #
Justin: we disagree. Wright’s shifting balance theory is probably just wrong, and epistatic effects not very important. As for all the good mutations already having happened – first, circumstances experienced by humans have been changing more and more rapidly, and what became advantageous recently was often not advantageous in the deeper past. Next, go calculate the expected time for the establishment of a nucleotide substitution with a 5% advantage in a population with an effective size of ~200,000, a reasonable Ne for 100,000 year ago. It takes a long time. It’s far more rapid in a population of tens of millions.
— gcochran · Feb 14, 08:57 AM · #
The problem is that evolution does not take place in large populations of any sort anywhere. It takes place in small populations. This is not a controversial or marginal point. Everybody who has read like one book on evolution should have stumbled on this.
— Fred Hapgood · Feb 14, 06:05 PM · #
Fred, my problem is that I have read many books on evolution, not just one.
— gcochran · Feb 14, 07:28 PM · #
Bacteria evolve rapidly: antibiotic resistance, you’ve heard of it? Their population size is large. Insects develop resistance to insecticides. That resistance appears more rapidly the larger the population, and it usually takes the form of a single key mutation, rather than multi-gene effects.
Look at the house sparrow (also called English sparrow). It did not colonize North America until 1852, but that has been long enough for the evolution of regional races that differ in color and size. Was this something that happened in a tiny population? Nope: there may be as many as 400 million of the nasty things in North America.— gcochran · Feb 14, 08:23 PM · #
“With nothing but Mendel to work with, Darwin’s own grand hypothesis was wildly speculative at the time.”
Just want to point out that Gregor Mendel’s famous paper on the laws of genetic inheritance was not written until 1865, published 1868 and rediscovered in 1900. Obviously Darwin could not have drawn upon it in 1859, nor is Mendel’s name listed in the index to “The Descent of Man.” Does someone know if Darwin, who must have been well-read in natural science, ever cited Mendel in a minor paper or letter?
On the other hand, Darwin’s work was not as speculative as all that. Alfred Wallace had more or less the same theory, and plenty of evidence turned up as soon as people started seriously looking for it in the decades after “The Origin of Species” was published. Also, as you alluded to, evolution of natural species was an idea in the air since the late 18th century. I know you’ll find it mentioned in Goethe and Keats (and one of Disraeli’s novels), but I don’t know enough to say which scientists took up the subject.
— Paul · Feb 15, 02:00 AM · #
And yet, here in the real world, smallpox – along with 99.9999% of all species that have ever existed – is extinct.
Proponents of the idea that “victory in biological war is impossible” need to grapple with the fact that defeat in biological war is not only entirely possible, but common and widespread. It’s true that our efforts to combat disease apply a selection pressure to those organisms to evolve countermeasures to our efforts.
The problem for Noah is that there are actually two ways for a population to respond to a selection pressure: 1) adapt to it, or 2) become extinct. I realize it’s advantageous for conservatives to pretend that the second can’t possibly ever happen, but people who would like to live in the real world don’t have that luxury.
— Chet · Feb 16, 12:08 AM · #
We cannot defeat disease, for example, merely hold it at bay, because our most successful efforts are precisely those that put selection pressure on microorganisms that will result in new diseases able to thwart our countermeasures.
As Chet points out, selection pressure does not cause mutations nor can mutations necessarily make everything possible (contra X-Men), so it is not inevtiable that all countermeasures will be thwarted.
Moreover, the assumption here is that virulence is an advantageous trait, or at least a neutral one, in diseases, and that the way that a microorganism will evolve to adapt won’t be to stop causing disease (at least cause much less harmful disease) so that the host organism doesn’t try to get rid of it anymore.
I was under the impression that part of the reason why AIDS has become more manageable is not just the advent of HIV-inhibiting drugs, but the fact that, particularly with a somewhat less promiscuous gay population in the late 80s to at least the mid-to-late 90s making the disease spread slower, less deadly strains had a better chance of surviving and spreading.
— Glaivester · Feb 16, 03:39 AM · #
What’s really remarkable about Cochran’s posts is their sheer efficiency. I’ve seen a lot of effective arguments made on this board, but I can’t remember any that were so direct.
— J Mann · Feb 18, 04:13 PM · #