The BBC reports on intriguing new research positing, on the basis of DNA evidence, that human evolution has sped up dramatically—perhaps by a factor of 100—over the last 5,000 years. The study authors offer growing population size as a possible explanation. This makes some intuitive sense: More organisms mean more opportunities for new genetic variations to arise, and a more spread out population means more opportunity for those variations to incubate somewhat independently without being totally isolated. But if that alone sufficed, we should expect to see evidence of even more pronounced discontinuities in other, still more numerous organisms.
For readers of Geoffrey Miller’s fascinating treatise The Mating Mind, another explanation springs readily to mind. Miller argues for the evolutionary centrality of mating selection. Miller contends that a hardwired sexual preference for a certain trait—like the peahen’s preference for peacocks with large, bright plumage—can trigger a kind of arms race or feedback loop. The outliers in one generation, precisely because they’re so reproductively successful, become the baseline above which the next generation’s mating-game winners must rise.
A process like this, says Miller, may account for our most advanced cognitive and artistic capacities. A preference for mates capable of performing complex tasks—composing a song or a sonnet, or deciphering ever changing cultural codes and fashions—may have emerged as a proxy for a sound genome, as the delicate and byzantine brain would be disrupted by mutations that might otherwise pass undetected by the naked eye. Once established, though, the preference would create a runaway effect detached from its original purpose.
The thing is, explanations of this kind require (for lack of a better term) some evolutionary slack. The peahen-peacock feedback loop can generate enormous, colorful tails that are highly maladaptive in terms of pure survival… but only if they aren’t so onerous that old fashioned natural selection preempts mate selection. If an area is so rife with predators that the supermodel peacocks become lunch before reaching reproductive age, the peahens will end up making do with drabber birds whatever their preference.
But with that background in place, it’s not hard to imagine why human evolution might have accelerated over the past five millennia. In fact, it’s precisely the reason why, on a cruder view of how evolution works, one might have expected evolution to halt: Our growing mastery over nature. For the most primitive humans—life nasty, brutish, short, and so on—skill in elaborate wooing rituals would have taken a distant second place to surviving long enough to woo. Survival adaptations would have priority, and the same sorts of adaptations would have been vital everywhere: Strength, stamina, visual acuity, a hardy immune system. The more we’re able to shelter ourselves from the elements, to treat wounds, to establish stable food supplies, the less central these features become: The sickly guy with bad eyesight makes it to adulthood too. That means, first, selection pressure for convergence on certain traits is weakened, which might in itself be a source of variety. Second, it allows mate selection—in which large long-run effects can be locked in by what amounts to genetic noise, the proverbial butterfly flapping a tsunami—to get in the driver’s seat.
All this is, obviously, armchair speculation, but I’m curious whether folks find it plausible… in particular, any folks more qualified than I to speculate.
15 responses so far ↓
1 Fred S. // Dec 11, 2007 at 1:54 pm
So, let’s see… Sanchez accepts that human evolution has accelerated over the last 5000 yrs (that is, after having left Africa) but refuses to believe that there are meaningful geographic/racial differences in intelleigence.
So, this accelerating adaptation happened in exactly the same way at exactly the same speed everywhere on earth simultaneously.
I think I have found a belief-system stupider and more improbable than Mormonism.
2 Julian Sanchez // Dec 11, 2007 at 2:53 pm
” I think I have found a belief-system stupider and more improbable than Mormonism.”
Indeed you have; let me know how the new faith works out for you.
3 Adam // Dec 11, 2007 at 3:07 pm
Couple of thoughts:
1) Just by the way of background, the general phenomenon described here is called sexual selection, and Darwin himself is the one who first hit on the idea. I haven’t read Geoffrey Miller’s book, but I’m guessing that his purpose is the application of this well-founded theory to human cognition.
2) The theory certainly has some surface plausibility. As we get further from the tooth and claw aspects of nature, cultural/sexual selection factors could begin to dominate, and these could push adaptive changes more quickly (and also, in a certain sense, in more arbitrary directions). That said, though, it’s not clear exactly how far we really are from the tooth and claw aspects of nature. Disease still claims a lot of lives — and indeed some have posited that much of evolution is basically a race against microbes. And there are of course well-known interactions between wealth and fecundity. So basically, this is a complicated topic.
3) Fred S.’s comment is wonderful encapsulation of the allure of racist scientism. There are so many fallacies packed into one single sentence, it’s hard to know where to begin. The major one is the assumption that adaptation means monotonic improvement against some external metric. No wait, I can’t really say which the major one is.
4 Fred S. // Dec 11, 2007 at 3:43 pm
“The major one is the assumption that adaptation means monotonic improvement against some external metric.”
Uh, no, Adam; that you could infer that is mind-boggling. My statement assumes that evolution/adaptation means change prompted by environmental factors. During the past five thousand years of (apparently) accelerating volution, mankind was spread over the face of the earth and thus faced a variety of divergent environments.
Now, the onus is on you (or the proprietor of this blog) to explain either i) this evolution had no effect on intellectual capabilities or ii) such evolution as did occur affected every group’s intellectual capabilities identically.
Or you could either treat this statement as infra dig (Sanchez’s approach) or call me a racist (yours). Both are marvellously-effective rhetorical tacks.
5 BostonSatyr // Dec 11, 2007 at 6:52 pm
I think that Sanchez misses the true advantage of our tool-creation and critical thinking skills adaptations. Instead of these skills being useless until we’re adults (and thus we’d get killed off before tool-creating, etc. would be useful), these skills allowed early man to to thrive, and thus reproduce plentifully and spread across the world.
Due to our ability to invent and learn quickly, we had more time to continue creating and thinking of new ways to save labor, protect ourselves, and develop material comforts. Instead of feeding and fleeing all the time, the adaptation of an advanced mind allowed us to have more and more control over our paths and safety. Because of our advanced minds, we do a better job protecting our young by developing weapons to fight off predators, keeping fires, etc. So I think, Sanchez, that actually these adaptations protected us throughout life, since there would always be adults around to who COULD take advantage of these adaptations while protecting their young. Thye peacock may be a bad analogy.
However, at the same time, our larger, more advanced brain came at an extreme price. Human babies are born extremely helpless. Newborn’s brains are underdeveloped on purpose so they may pass through the narrow birth canal. This means human children require more care than any other mammal. A Terrible price to pay for our intellect.
Thoughts?
6 Julian Sanchez // Dec 11, 2007 at 7:31 pm
Sorry, I guess I was vague here. I was imagining the tool-making brain as part of what *provided* the mastery of nature that allowed the feedback-loop to kick in, not as itself the product of the feedback loop.
7 Daniel // Dec 11, 2007 at 9:24 pm
When I read this story earlier it seemed to me like bullshit–I am firmly of the (non-scientific)opinion that “evolution” is no longer acting on us. The trick, of course, is in the quotes.
I’m not anywhere near as pessimistic as Mike Judge (the movie Idiocracy really NEEDED to be referenced in this discussion. I was just here to make it happen.) but it seems as if pretty much anyone in this day and age can find a mate and reproduce–the number of people being “weeded out” has got to be very low, relatively, and mostly represents pruning.
But then, I’m talking about something else… I once read Christopher Hitchens say that he had hope for evolution to be an advancing force in the world; this struck me as actually kind of poignantly naive for such a truculent firebrand. In other words, it seems wrong to think that the force that brought us from just another ape to sentient human will continue its trajectory.
When the researchers in that story talk about evolution what they are really commenting on is the growing variety and changing nature of our genes–which, seems to me, probably has more to do with, I don’t know, the population than anything else.
8 Daniel // Dec 11, 2007 at 9:33 pm
Sorry, the last point I meant to make was that people would read that report, see “evolution” and think either that we will soon be able to move planets with our minds, or that the selection of our genes will soon usher in an age of peace and tranquility. Really what this “feedback loop” probably means, on the grand scale, is that we’re in an evolutionary tide pool, or rather one of those pockets of stillwater on the side of a creek.
9 LP // Dec 11, 2007 at 10:20 pm
1. Fred S. misses an important point, which I think has been made right here at least 3,000 times: it is absolutely consistent to believe that (a) evolutionary forces may have affected the cognitive attributes of certain groups (racial, gender, whatever) in diverse ways, leading to some genetic difference in average group intelligence, BUT (b) tests claiming to measure ‘intelligence’ are biased enough that the results they produce have more to do with the testing methods than with any measurable difference in actual intelligence, AND/OR (c) any putative genetic component of intelligence is dwarfed by natural variation between individuals of the same group, making it pretty much irrelevant.
2. Daniel — what? Within the scientifically literate community, ‘evolution’ just means ramdon genetic mutation plus selection by virtue of death or reproductive failure — movement away from specific failures, but not towards any specific success or goal. I don’t think anyone here interprets ‘evolution’ to mean ‘progress,’ which seems to be what you’re concerned about. Outside the scientifically literate community, I think most people who don’t actively reject evolution regard it as a neat device invented by God. This raises an interesting question, though — if evolution is working faster, do ‘intelligent design’ theorists believe we are being pushed closer and closer to the ultimate state of humanity God has in mind? In other words, is this a sign of the apocalypse?
3. One of the geneticists commenting in the BBC article espouses exactly the ‘cruder view’ of evolution you mention, noting that since survival-selection pressures have eased, we should expect to see that evolution is now slowing down dramatically, at least until the arms race with the microbes starts. I am probably not qualified to comment on whether your mate-selection theory is plausible, but it’s worth noting that one of the recent and widespread changes the article mentions is fair skin and blue eyes in Northern Europe, traits that are believed to be linked to mate-selection (rather than survival-selection) in cold climates.
4. ‘The Supermodel Peacocks’ = good name for an ironic post-punk band?
10 Daniel // Dec 11, 2007 at 11:08 pm
Wasn’t talking about you guys… more about the pop science reporting and how it’s interpreted by most people, which is that evolution is when the wind and rain works for years and years to form… Mt. Rushmore, presidents and all.
11 Daniel // Dec 11, 2007 at 11:22 pm
For example:
http://andrewsullivan.theatlantic.com/the_daily_dish/2007/12/the-next-paradi.html
12 BostonSatyr // Dec 11, 2007 at 11:26 pm
I agree with Daniel – there often is a dissonance between scientific understanding of a concept and the general public’s, especially those with no scientific experience beyond a few Bill Nye the Science Guy reruns (i.e. creationists trying to claim that the Grand Canyon is evidence of Noah’s flood).
One thing that bothers me about the race/IQ story is the way we measure IQ. I remember an article about five years ago being published that claimed the way we test IQ creates results that fall along racial lines, the same way standardized tests do. It’s not that people of different races have different levels of intelligence. Instead, they have different attitudes based on their upbringing and neighborhood culture, regarding tests and whether actually trying to puruse scholarly things like IQ tests will ever do them any good. I wonder if they were to compare children of different races, but raised in the same neighborhood/culture, and then see if there were disparate results. My guess is that there would be insignificant differences.
13 Glen // Dec 12, 2007 at 12:58 am
“Within the scientifically literate community, ‘evolution’ just means ramdon genetic mutation plus selection by virtue of death or reproductive failure — movement away from specific failures, but not towards any specific success or goal.”
True, but the study doesn’t say there has merely been faster evolution (in the sense of genetic change over time), but faster positive adaptation, meaning the emergence and spread of traits that enhance survival and reproduction.
“but it seems as if pretty much anyone in this day and age can find a mate and reproduce–the number of people being “weeded out” has got to be very low, relatively, and mostly represents pruning.”
The study shows that positive adaptation has accelerated in the last 5000 years. The last 200 or so years, which is the period during which capitalist wealth plus welfare statism might possibly have made it possible for “pretty much anyone” to breed, is just a blip at the end of that 5000-year time period.
14 Rice // Dec 12, 2007 at 6:57 pm
Just in case any of you are interested, one of the authors has a somewhat simplified description of they believe is occuring on his website. Be warned that its long, but it may help clear up some of the confusion I see here.
http://johnhawks.net/weblog/topics/evolution/selection/acceleration/accel_story_2007.html
15 Julian Elson // Dec 13, 2007 at 12:16 pm
In practice, though, how does this happen? It seems to me that if you’re smart, funny, etc, you’re more attractive, to be sure, but does that really improve reproductive success? It seems to me that the main benefit of being attractive is getting an attractive mate, which is nice for you, but doesn’t mean you have a bunch of kids. Your husband doesn’t have to be tall, dark, or handsome to knock you up, nor does your wife have to have a brilliant sense of humor and perfect white teeth to get knocked up.
It seems to me that social class could be important, since wealth can provide a lifestyle which leads to somewhat reduced infant and childhood mortality. If selected factors lead to wealth, as Gregory Clark hypothesizes, then that could work. Another trait that might be selected for is a sheer desire to have kids — at least, in times when this was often a matter of choice.
Maybe I’m just thinking too much of sexual selection in terms of “the right tail of the funny/smart/sexy bell curve has great reproductive success,” rather than “the left tail gets cut off,” where the most inept/unattractive people don’t find mates even among each other. Over time, though, I suppose the effect would be the same.