Study finds humans still evolving, and quickly
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 historic levels after agriculture became widespread, according to a study published today.
By examining more than 3 million variants of DNA in 269 people, researchers identified about 1,800 genes that have been widely adopted in relatively recent times because they offer some evolutionary benefit.
Until recently, anthropologists believed that evolutionary pressures on humans eased after the transition to a more stable agrarian lifestyle. But in the last few years, they realized the opposite was true -- diseases swept through societies in which large groups lived in close quarters for a long period.
Altogether, the recent genetic changes account for 7% of the human genome, according to the study published in the Proceedings of the National Academy of Sciences.
The advantage of all but about 100 of these genes remains a mystery, said University of Wisconsin-Madison anthropologist John Hawks ...
Most of the genetic changes the researchers identified were found in only one geographic group or another. Races as we know them today didn't exist until fewer than 20,000 years ago, when genes involved in skin pigmentation emerged, Hawks said. Paler skin allowed people in northern latitudes to absorb more sunlight to make vitamin D.
"As populations expanded into new environments, the pressures faced in those environments would have been different," said Noah Rosenberg, a human geneticist at the University of Michigan, who wasn't involved in the study. "So it stands to reason that in different parts of the world, different genes will appear to have experienced natural selection."
Hawks and his colleagues from UC Irvine, the University of Utah and Santa Clara-based gene chip maker Affymetrix Inc. examined genetic data collected by the International HapMap Consortium, which cataloged single-letter differences among the 3 billion letters of human DNA in people of Nigerian, Japanese, Chinese and European descent.
The researchers looked for long stretches of DNA that were identical in many people, suggesting that a gene was widely adopted and that it spread relatively recently, before random mutations among individuals had a chance to occur.
They found that the more the population grew, the faster human genes evolved. That's because more people created more opportunities for a beneficial mutation to arise, Hawks said.
In the last 5,000 to 10,000 years, as agriculture was able to support increasingly large societies, the rate of evolutionary change rose to more than 100 times historical levels, the study concluded.
Among the fastest-evolving genes are those related to brain development, but the researchers aren't sure what made them so desirable, Hawks said.
There are other mysteries too.
"Nobody 10,000 years ago had blue eyes," Hawks said. "Why is it that blue-eyed people had a 5% advantage in reproducing compared to non-blue-eyed people? I have no idea." [MORE]
And from The Telegraph in Britain:
Humans 'evolving to have children later'
By Roger Highfield, Science EditorLast Updated: 10:01pm GMT 10/12/2007Good news for future generations of career women: we are evolving to have more children later in life, according to a recent study.
Humankind has evolved more rapidly in the past 5,000 years, at a rate roughly 100 times higher than any other period of human evolution. And an author of the study predicts that this suggests humans will further evolve to have more children later in life. [MORE]
My published articles are archived at iSteve.com -- Steve Sailer
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27 comments:
They found that the more the population grew, the more the human genes evolved? What a body blow to the Rushtonian Model of Arctic adaptation.
Since blues eyes are the result of recessive genes, it takes two blue eyed parents to produce a blue eyed baby. If there is a brown eyed baby with blue eyed parents mom has been messing around. It is a good first test of paternity.
I read the article on humans becoming able to have children later but because Highfield seemed to be discussing this in terms of health in later life, I felt it was lacking a dimension. I've personally known of a family where some of the women didn't reach puberty until after age 16 and were still able to have children. They tended to be taller than average and still very feminine despite the delay. This is what I'd consider the kind of genetic variation that would be a great advantage in a society where women wait until their 30s.
Both these articles have been thought provoking but I can't help being skeptical. I've wondered if the variations that made one group more adaptable to say a society where women wait until 30 to have children haven't been present in some populations all along. What if this was true of a group of Scandanavians centuries ago but their population was greatly reduced by war or famine or another group say of early maturers became the dominant population because of having children early and often? To me, the variations wouldn't necessarily have to be new but weren't noteworthy until scientists found a use for them i.e. the later maturing, later menopause, longevity link becoming apparent as some women discover they can't delay childbirth. Of course, I guess this is my perspective that 10,000 years ago was a long time ago so how could anything that emerged then be new.
The brief coverage of diabetes can be very misleading. I think there are genetic and environmental factors at play here more than the simplistic treatment of it as some sort of trait that is present or not present indicates. Note, I have only read about diabetes and not studied it and maybe misunderstood some of what I read.
Diabetes itself is a complicated subject. I've read that a mother who has gestational diabetes has to control her bloodsugar carefully or else risk compromising the embryo's ability to metabolize glucose. This means that diabetes might be triggered in the womb as much as by genes. So maybe Highfield's article has provided us with useful information or maybe he's not really on the right track yet.
Related to the diabetes-fertility-longevity discussion is the fact that some endocrinoligists theorize that childhood obesity in girls and to an extent in boys disrupts normal hormone functioning. In girls this often leads to earlier puberty but with reduced fertility. Diabetes/insulin resistance is part of the reason for this. Unfortunately, we now have a generation of children who will be the evidence whose fertility in later life will either prove or disprove the link between childhood obesity and fertility problems even in adults who are of normal weight.
The interaction of genes and environment, in this case nutrition, can't be ignored. I've already tried to follow several trains of thought on the consequences of childhood obesity but even that can be difficult since it may not be the obesity but the correlation with diabetes that determines how long a person is fertile. So the problem may end up being not so much that some people can eat lots of sugar/carbs and some can't but instead nutrition in general. I think a look at groups with a history of vegetarianism might shed some light on this, especially in India where you have two groups of similar genetic make-up, one eating a presumably lower carbohydrate diet b/c they also eat meat, the other probably eating many more carbohydrates by deriving their proteins from a combination of grains and legumes. Both groups seem to have a tendency toward diabetes - but this b/c of sugary snacks or too many carbs period.
While I'm not always an advocate of nurture over nature, I think when it comes to nutrition, it's not so easy to distinguish the two.
Bill,
It does not take 2 blue eyed parents to make a blue eyed baby. A mother can have blue eyes and a father green eyes (like mine), and the kid can still have blue eyes (like me). Dad could have had brown eyes, and I still might have blue eyes.
It IS genetically almost impossible for 2 blue eyed parents to produce a brown eyed child without some profoundly unusual mutation.
hoosier comrade - I dont have your genetical edumacation but couldnt both be true?
Hoosier,
Doesn't Rushton himself explain the low IQs (around 90) of some nomadic Arctic peoples (i.e. the Inuit) based on the fact that their populations never became large enough for advantageous mutations to develop and spread?
bill,
not if one brown eyed parent carries the recessive blue-eyed gene.
Do you know anything about Punnett squares bill? For a single locus dominant recessive allele model, you could have two brown-haired people producing a blue-eyed child.
MarcZ,
I'm unfamiliar with that. Do you happen to know where he argues that?
I must say I'm a bit suspicious of that explanation, given how well they have adapted for resistances to starvation and exposure.
Hoosier, explain the body blow? I'm not seeing how they're mutually exclusive.
Yep, my paw had brown eyes, my maw has blue eyes, and I have blue-green eyes.
They found that the more the population grew, the more the human genes evolved? What a body blow to the Rushtonian Model of Arctic adaptation.
First, what is this model of arctic adaptation? I read Rushton's book, and that doesn't appear to be part of his theory. He speaks of adaptation to "predictably cold environments".
Second, how does this study (really, a statement of the obvious) deliver a "body blow" to Rushton's theories?
I have no idea what your point is supposed to be.
Svigor & Ben Tillman,
1. Rushton suggests that selection for K-strategy occurred in "predictably cold environments".
2. Cochran et al. indicate that selection for K-strategy occurred in the most populous regions.
3. The archaeological record indicates that population density was greatest in the temperate belt, not in the "predictably cold environments".
This appears to me to undermine the "predictably cold environment" selection model.
They appear mutually exclusive to me.
Perhaps somebody can explain to me where I went wrong.
Hoosier Comrade - Im still not seeing mutually exclusive.
hoosier comrade responding to markz: "I must say I'm a bit suspicious of that explanation, given how well they have adapted for resistances to starvation and exposure."
1)The inhabitants of far N. America came from siberia. Thus they would already be adapted to similiar conditions of "starvation and exposure" when they arrived in N. American
2)Here is a way Rushton and Cochran et al. can be reconciled: Large populations in the temperate zones could have provided the wellspring for mutations for higher intelligence. North-South gene-flow could have spread those mutations North, where harsh conditions made them even more valuble than in the South. Thus, cold environments still forced humans to gain a higher intelligence to adapt, but the populous south is where those high intelligence boosting genes mainly flowed from. Does this sound plausible to anyone else?
I wonder what things such as insulin and anti-biotics will do to the human race. Perhaps we are in for one hell of a die off when some super bug evolves. We have been keeping people, and now generations of people alive that would have kicked the bucket long before.
Cochran et al. indicate that selection for K-strategy occurred in the most populous regions.
They do? Where?
Rushton suggests that selection for K-strategy occurred in "predictably cold environments".
He theorizes that "predictably cold environments" selected for intelligence and foresight, not K-strategy.
The archaeological record indicates that population density was greatest in the temperate belt, not in the "predictably cold environments".
The temperate belt is where these "predictably cold environments" are found.
pjgoober,
Your reconciliation seems possible, though I don't see how it's more parsimonious than the proposition that the populous temperate regions both created and multiplied K-strategy traits.
Why involve the "predictably cold environment" selection if it's not necessary to explain anything?
Ben,
Cochran et al. indicate that the recent and rapid selection among European and East Asian populations happened along with higher population densities. They even hypothesize that the increased rate of evolution may have been the result of the increased population size.
It was perhaps an inference on my part to describe that rapid selection as selection for K-strategy traits.
Rushton's "Race, Evolution, and Behavior" is available for download online and ties the "predictably cold environment" explanation in with selection for K-strategy traits. I don't see how it could be interpreted otherwise.
North Africa, Southern Europe, the Levant, Mesopotamia, Persia, the Indo-Gangetic Plain, and the Chinese Basin are all temperate, all have (pre-)historically high population densities, and were not all that cold.
There are a bunch of human populations which existed to the North of Caucasians - Saami, Turkic, Altaic, Mongoloid, and Eskimo nomads. The "Nordic" people invaded Scandinavia recently from the Southeast, displacing the indigenous Saami with superior technology, not superior environmental adaptations.
Hoosier, your fundamental misapprehension is reflected in your initial comment:
"What a body blow to the Rushtonian Model of Arctic adaptation."
Rushton does not propose a model of arctic adaptation. One problem may be that Rushton seems to use his term "predictably cold environment" to mean two different things. In the conext of intelligence adaptations, it refers to an environment in which there are cold WINTERS, not cold summers. People have to plan ahead for periods of relative scarcity. He is not talking about the arctic.
When it comes to the r-K issue, Rushton uses the same term, but in that context it refers to an environment that has low resource density, i.e., one that is simply cold.
K strategies develop where the population is dense compared to the available resources, and where children require extra care.
R strategies develop where a resource-rich environment is periodically depopulated, and where a milder environment lessens the care required by a child, making it adaptive to produce many children quickly. Thus, his theory is that high population density produces k strategies. That should be obvious if you think about what "k" refer to: carrying capacity.
A k strategy is a strategy employed where the population is at its carrying capacity, i.e., maximum density.
Ben,
Scarcity would naturally result in optimizing for caloric efficiency, with adaptations for efficiently storing energy. This is why you have short, obese, and relatively unintelligent populations in regions where they've adapted to (seasonal-) scarcity.
If contemporary Europeans, Semites, and East Asians didn't inhabit the mild Mediterranean belt then who did? Where is this r-strategy adapted population that should be there?
Why haven't the African Bushmen, who suffer from seasonal scarcity, become gifted and tall?
How come, if regular depopulation causes r-strategy, the population with the fewest proven bottlenecks (Africans) are among the most r-strategy selected while Europeans and Jews, who have suffered several severe bottlenecks, are K-strategy selected?
Hoosier Comrade
The theories aren't at all necessarily incompatible. Neither claims exclusivity, or certainly the Hawks, Cochran et. al. paper doesn't.
Rushton’s and others’ theories that races which long inhabited colder regions faced selection pressure towards greater K behavioral patterns (parental and in Rushton’s theory specifically father investment in each child - as opposed to having more of them = R), and also pressures for greater abstract, foresight types of intelligence, as well as visio-spatial acuity useful when a large part of the diet comes from big game hunting with it’s concomitant dangers, is not inconsistent with Hawks & Cochran et. al.’s theory that the much greater population numbers enabled by agriculture greatly accelerated human evolution thereafter. Rather the two theories are orthogonal to each other.
For one thing Rushton focuses on a limited subset of evolved traits, mostly intelligence and parental investment in children, rather than the totality of changes as Hawks, Cochran et. al. do, at least in this acceleration paper. As Hawks notes at his site, a great many of the selected mutations had to do with adapting to diseases which also arose or became much more prevalent after the rise of agriculture and animal husbandry, and others look related to adaptions to changed dietary mixes. (However I think we will see in subsequent papers that a lot as well seem related to brain / behavioral adaptations, which would include not only IQ but personality shifts as well.)
For another, even if evolution greatly accelerated after the peak of the last ice age, that is after 18,000ya, subsets i.e. certain races of humanity spent a very much longer time in cold regions bordering the glacial regions before the neolithic revolution had become quite widespread in some areas 8,000 ya. Specifically the Eurasian-African split may have occurred some 90-100 kya years ago (there are remains in Israel that date from 93 kya, and the European-East Asian split some 40kya. (Austronesians probably split from Africans or proto EurAsians some 60-70kya.) Those are long periods of time for basic racial differences to have developed under different environmental and consequently cultural selective pressures, even if they were occurring much more slowly per year than became the case after the earliest rise of agriculture.
However, it now becomes fully plausible that differences between sub racial or even sub-sub racial groups (ethnic groups), which split apart as largely endogamous breeding groups much more recently, might be partly or largely genetic in origin, rather than necessarily being only cultural. This was more than hinted at in the case of specifically Ashkenazi Jews in Harpendig’s and Cochran’s paper two years ago, when the 2/3 or so SD elevation of Ashkenazi Jewish intelligence over than of the sea of Europeans they lived amongst, was posited to be largely genetic (or anyway inextricably so – there are positive feedback loops) and to have occurred entirely or almost entirely during the middle ages, over a period of only some 1,000 or even 800 years.
I.e., it could be that Eurasians who lived in fairly northern or anyway cold regions for a long time(NE Asians and Euros) have 1-1.25 SD’s more IQ than s.S. Africans and have other personality/behavioral differences on average largely for reasons Rushton describes, but that some groups of each are quite different from others due to more recent evolutionary changes associated with the rise of agriculture and greatly increased population sizes (and literacy at least among fairly broad elites, in some cultures/places.) Or maybe say half of the IQ difference in e.g. Euro and NE Asians was due to long periods in cold places, and half is due to agriculture and higher densities much more recently, but for a lot longer than Africans.
dougjnn,
You raise a compelling example of how the two models could be compatible, with the Rushton model covering paleolithic adaptations and the Cochran model covering neolithic adaptations. It certainly seems like a sensible and possible explanation.
My hesitation lies in the fact that Cochran's model offers hard evidence for the correlation between population growth and K-strategy adaptation while the Rushton model is largely speculative and not, to my knowledge, falsifiable (yet).
So my proposition is that Occam's Razor implies that we have a model with hard evidence that is falsifiable which can explain the adaptation. Why bother to add the Rushton model unless the Cochran model somehow proves lacking? What value does it add to offer the dual explanation when one explanation can do it?
Perhaps I can summarize my general apprehension about the Rushton model like this...
It seeks to explain the development of populations which are profoundly less efficient with caloric energy by suggesting that they migrated to regions that had profoundly fewer calories. It seems like an outright contradiction to suggest that the threat of starvation and exposure selected for populations more vulnerable to starvation and exposure.
They're MORE efficient with caloric energy.
Ben,
Caucasians and East Asians have higher resting metabolic rates and store fewer of the calories they consume. Populations that have ACTUALLY been selected for cyclical scarcity are the Khoi-San, the Indigenous Australians, the Eskimo, and the (famously obese) Pima.
For the cost of a travel to the Kalahari Desert, you can hang out with Brangelina and see exactly what features cyclical scarcity produces. You're even welcome to adopt one of the humans that would have otherwise been selected by scarcity. They're the hot new status symbol.
Resting Metabolic Rate in African-American and Caucasian Girls
http://www.obesityresearch.org/cgi/content/abstract/5/4/321
Do African-Americans have Lower Energy Expenditure than Caucasians?
http://www.nature.com/ijo/journal/v24/n1/full/0801115a.html
Risk Factors for Heart Disease
http://www.cdc.gov/DHDSP/library/aian_atlas/section_three.htm
(see Figures 4, 6, and 7)
Hoosier comrade said-
Why bother to add the Rushton model unless the Cochran model somehow proves lacking? What value does it add to offer the dual explanation when one explanation can do it?
The region with the longest history of agriculture is the middle east, and yet the average IQ there is only around 90, or even a bit lower. Yes it’s considerably higher than the average African (in Africa) IQ of around 70 (ten points of which low level Lynn estimates, on a more or less seat of his pants basis, to be due to often severe nutritional and disease load impediments there), but it’s much lower than the world’s two large racial groups scoring the highest – in order the NE Asians (Mongoloids) and European Caucasians. Both of the later groups appear to have spent tens of thousands of years adapting to and thriving in fairly cold regions which placed a premium on hunting rather than gathering, and storing food and fashioning shelter and clothes. These two broad racial groups also both enjoyed great population increases beginning some 8kya with the spread (or in the case of the NE Asians perhaps the independent invention) of agriculture, first in the more southerly parts of their regions.
As well the hunter gather peoples with the highest IQ’s seem to be those found either in the Artic or whose not so distant ancestors spent much time there (Inuit and Amerindians generally), rather than those found in Africa, Australia or upland SE Asia.
It would help of course if we had a lot more IQ test results for hunter gatherer groups than we do, but this sort of thing has been highly sensitive for some time now.
The economist has an excellent and fairly long open access article on the Hawks, Cochran, Harpending et.al. acceleration paper.
dougjnn said...
The region with the longest history of agriculture is the middle east, and yet the average IQ there is only around 90, or even a bit lower.
One must consider the recent migration and integration of less intelligent populations when reviewing the Middle East. The Afro-Asiatic populations that established the Sumerian and Egyptian Civilizations were presumably very bright, as were the Hebrews.
There is a lot of historical and genetic evidence for Mongoloid, Turkic, Dravidian, and Congoid admixture in the Middle East within recent historical times. Geographically, those best-positioned to evade such migrations are the Europeans, who were not uniquely intelligent but uniquely fortunate.
Perhaps less than coincidentally, the most intelligent population in the world is the only Middle Eastern population that has developed a group evolutionary strategy to limit admixture.
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