Image: Owen Gildersleeve
In Brief
- As early Homo sapiens spread out from Africa starting around 60,000 years ago, they encountered environmental challenges that they could not overcome with prehistoric technology.
- Many scientists thus expected that surveys of our genomes would reveal considerable evidence of novel genetic mutations that have recently spread quickly throughout different populations by natural selection—that is, because those who carry the mutations have greater numbers of healthy babies than those who do not.
- But it turns out that although the genome contains some examples of very strong, rapid natural selection, most of the detectable natural selection appears to have occurred at a far slower pace than researchers had envisioned.
Thousands of years ago humans moved for the first time into the Tibetan plateau, a vast expanse of steppelands that towers some 14,000 feet above sea level. Although these trailblazers would have had the benefit of entering a new ecosystem free of competition with other people, the low oxygen levels at that altitude would have placed severe stresses on the body, resulting in chronic altitude sickness and high infant mortality. Earlier this year a flurry of genetic studies identified a gene variant that is common in Tibetans but rare in other populations. This variant, which adjusts red blood cell production in Tibetans, helps to explain how Tibetans adapted to those harsh conditions. The discovery, which made headlines around the world, provided a dramatic example of how humans have undergone rapid biological adaptation to new environmental circumstances in the recent past. One study estimated that the beneficial variant spread to high frequency within the past 3,000 years—a mere instant in evolutionary terms.
The Tibet findings seemed to bolster the notion that our species has undergone considerable biological adaptation of this sort since it first left Africa perhaps 60,000 years ago (estimates range from 50,000 to 100,000 years ago). The transition to high altitude is just one of many environmental challenges Homo sapiens encountered as it migrated from the hot grasslands and shrublands of East Africa to frigid tundras, steamy rain forests and sun-baked deserts—practically every terrestrial ecosystem and climate zone on the planet. To be sure, much of human adaptation was technological—to combat the cold, for instance, we made clothing. But prehistoric technology alone could not have been enough to overcome thin mountain air, the ravages of infectious disease and other environmental obstacles. In these circumstances, adaptation would have to occur by genetic evolution rather than through technological solutions. It was reasonable to expect, then, that surveys of our genomes would reveal considerable evidence of novel genetic mutations that have spread recently throughout different populations by natural selection—that is, because those who carry the mutations have more healthy babies who survive to reproduce than those who do not.
This article was originally published with the title How We Are Evolving.
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36 Comments
Add CommentAs I understand, there are also groups of native Americans who have lived in the Andes for some time and also seem to have developed special adaptations for high altitudes, although I understand they also attribute their abilities to some extent to chewing coca leaves. I think it'd be most instructive to determine whether these people have also developed the same rare gene variant as the Tibetans. If so, it could also constrain the upper boundary of time required for humans to develop functional genetic adaptations.
Reply | Report Abuse | Link to thisWhat does it mean ...than biologists would have expected....?
Reply | Report Abuse | Link to thisThis article just confirms what most would have been expected. No population with limited technology could adapt to high altitudes without physical gene selection. Why would anyone think that the Tibetans to have used technology. What technology? They had neither oxygen tanks or other equipment to combat the impact of high altitude living.
I believe I read somewhere recently that either the Andeans or the Tibetans developed a genetically detectable adaptation to high elevation but not the other. It probably isn't a novel genetic trait, [ a recent mutation] but merely a high concentration of a trait that occurs sporadically throughout the human population.
Reply | Report Abuse | Link to thisThe article claims babies with the trait survive better than those without it. I detect a hint of a general misconception of what evolution is. How about the idea that people who don't like high elevation stay away, a reproduce in the lowlands, and people who like high altitude stay, marry and reproduce in the mountains, with other like-minded people, thus concentrating in their children whatever genetic characteristics facilitated their finding each other. Evolution is not necessarily a life or death process. Darwin acknowledged that sexual choice of mates is, in some species, as much a driver of evolution and/or genetic drift over time, as stark environmental adaptation. I think choice of where to live may be a similar driver.
In other words the various altitude genes could easily have been among us, dispersed thinly in the general population, since we were homo erectus, been concentrated for a few thousand years at a time, then re-dispersed when a population again abandoned the highlands, during ice-ages for example.
I agree with all your observations. Probably not many people with heart, circulatory or anemic conditions chose to visit high elevations much less live and work there. The rare gene variant common in Tibetans may be common in all people with robust respiratory systems.
Reply | Report Abuse | Link to thisConversely, if Andean peoples do not have the rare gene variant as you recall it'd be interesting to understand what allows them to be productive at high altitudes. Perhaps chewing coca leaves would do it for everyone. The absence of the rare gene variant in the Andes may also indicate that it exists only in some particular segment of the world population.
Thanks!
Sorry - I meant to say "chose not to visit high elevations".
Reply | Report Abuse | Link to thisI recall that the military did several extensive studies on how to tell if individual soldiers would be suitable for duty in extremely cold battle fronts, such as defending Alaska during the winter. The military realized that there is a quite wide range of human ability when it comes to withstanding cold for long periods of time.
Reply | Report Abuse | Link to thisIt turned out that the best way to tell which soldiers would do well in a cold climate was simply to ask them if they would rather fight in conditions that were way too hot or way too cold. I think graycat is on to something with the idea that personal preference matters.
At one time I taught school in the tiny Eskimo village of Golovin, Alaska, and I had many conversations with the elders of the Inupiaq and Northern Yupik tribes that populated the village. The elders were concerned that the young people were losing all their bad weather and cold survival skills. What typically happens is that adolescents dress exactly like teens in LA or New York City, but the Eskimo kids are accustomed to jumping on fast snowmobiles and racing to see their friends in the next village.
Perhaps because they are cold-adapted genetically the youngsters tend to leave their parkas and mukluks behind and race off wearing Nike shoes, blue jeans, and thin synthetic jackets. If they get caught by a snow storm and lose visibility they will then perish because they are under-dressed.
The Eskimo had great natural technology for dealing with extreme cold, but technology is subject to social and cultural fashions and humans very quickly forget it. I once asked a village elder, Stanley Amarok, what was the coldest he had ever been. Without batting an eye he replied that during World War Two the government had evacuated all the residents of Golovin because of fear of the Japanese, who had invaded Alaska.
Stanley's family was relocated to Chicago, and he said that by far was the coldest he had ever been in winter.
Yeah, I expect you're right about the military funding studies to determine how to select individuals best suited for sever climates. In 1970 they sent me to Viet Nam for a year and then on to Germany. They rarely follow their own advice.
Reply | Report Abuse | Link to thisWhen first inducted they selected a bunch of us for testing to select soldiers for Officers Candidate School. A conscript could become a Second Lieutenant in a matter of weeks. So, they first gave some intelligence test, then called out the names of those to leave. Next the gave another test that asked questions like: 'do you like camping out?'; 'would you like to be a leader?', etc. Realizing that, in 1970, this was an opportunity to become a patrol leader in the jungles of Viet Nam, I failed that test miserably...
As far as I know, they don't have the same gene variant. Their "adaptation" also seems to have something to do with breathing deeper or something, more acclimatization than actual adaptation. Adaptation is not merely a question of time, it all depends on the actual variation arising and being common enough in the right place, at the right time. Even Tibetans still have sub-optimal genes for altitude in their gene pool. Natural selection, the process of individuals dying or reproducing more or less according to their phenotypes' fitness, is not a perfect filter for genetic variation. And it is even less efficient in intelligent and social species like ourselves.
Reply | Report Abuse | Link to thisWhereas I've said "the process of individuals dying or reproducing more or less according to their phenotype fitness", someone else made a good point emphasizing better that the process is not necessarily as deadly as this description could suggest. Might well be that in cases like these, as people move around, some people just realize they don't feel so well in higher altitudes, and move somewhere else, while others don't feel that bad and stay there. They could even have some folk knowledge that some people naturally feel better or worse at higher altitudes and other ways that it affect the health of some people, I guess, and that could help driving selective migrations, on either direction.
Reply | Report Abuse | Link to thisWell put: interesting points. Thanks!
Reply | Report Abuse | Link to thisIn 1997 I went to Tibet With some pilgrims for Mansarovar and Kailash Yatra.When we entered in Tibet on 14000 feet high naturally oxygen level gave some of us trouble of breathing.This trouble remain three days after that our body made adjustment with that climate and trouble stopped. We spend 18 days in Tibet no one suffered in taking breath.I think our body have power to adjust unfavourable weather. No concern of gene.
Reply | Report Abuse | Link to thisThere is a demonstrated period of adjustment to higher altitudes. In the U.S., Colorado Springs, at 6,000 feet, is the location of our Olympic training facility, since physical training at higher altitudes both prepares athletes for performing at mountainous locations and provides an advantage for performing at lower altitudes when opponents have trained at lower altitudes.
Reply | Report Abuse | Link to thisOver many years, I made perhaps dozens of work week long (non-athletic) trips to Colorado Springs. Although reasonably fit and athletic, I always experienced somewhat serious shortness of breath just walking up staircases even after 4-5 days at 6,000 feet. I don't think I could possibly have survived at 14,000 feet without auxiliary oxygen.
I should mention that I've now developed a heart condition that may have been contributing to my difficulties. I think, though, that many people could not easily adapt to especially very high altitudes.
Just to clarify; Tibetans developed more efficient circulation and more red blood cells. Andean peoples developed larger lung capacity. A crossing of the two traits may result in the ultimate thin atmosphere adaptation.
Reply | Report Abuse | Link to thisIn ‘How Are We Evolving’ many intriguing findings show how complex is the process of evolution by Natural Selection. Clearly the environmental pressures Professor Pritchard speaks of should include those created by humans. This feedback loop (of ‘artificial’ influences introduced by man into the environment) surely accelerates the ‘selection’ process, mainly for humans, but for other species, too.
Reply | Report Abuse | Link to thisOne view is that humans are not Naturally Selected at all: the allele most helpful to humans was probably that which gave rise to recall. It was recall which may have catapulted humans outside ‘natural’ selection pathways. In the book ‘Dangerous Mind – On the Origin of Pseudo Species’, a distinction is made between humans and other species, which (like primates), though strikingly similar genetically, exhibit strikingly different behaviour.
I’m especially intrigued at the finding that ‘a helpful allele could become fixed in as little as a few hundred years if it conferred an extraordinarily large advantage’.
This, in my view, exactly fits the characteristics of recall; conferring a mental advantage that propelled humans faster than Natural Selection ever could. Mental ‘leverage’ outstrips Natural Selection.
It may not be that Natural Selection merely ‘acts relatively weakly on individual alleles’, as Professor Pritchard states; could it not be that, having been endowed with recall and the
whole panoply of mental abilities thus engendered, that natural selection for humans is redundant, and has been for millennia? Clearly we are not evolving, but the tools and systems we have invented are.
Did this unique Tibetan factor not also work to their detriment in the 1960's when hundreds of thousands, who were given land in southern India, had expired because they couldn't cope with the lack of altitude?
Reply | Report Abuse | Link to thisExcellent article. The second last paragraph begins:
Reply | Report Abuse | Link to this"In the developed world relatively few people die between birth and adulthood, so some of the strongest selection forces are probably those acting on genes that affect the number of children each person produces. In principle, any aspect of fertility or reproductive behavior that genetic variation affects could be the target of natural selection."
In the developed world, one of the strongest factors affecting family size may be culture or religious belief. This leads me to wonder if scientists, skeptics, and/or atheists have genetic variations in common, and if those with strong religious beliefs have genetic variations in common. As the article states these traits may be selected by a suite of genes, which would make it difficult to tease out differences.
Are couples who chose to reduce their family size to reduce the stress on our environment and on diversity, affecting natural selection? Do couples who choose to have large families because of cultural attitudes or religious beliefs affecting natural selection even more powerfully?
Religious beliefs have changed dramatically in the last 60,000 years. Have changes been the result of natural selection or are the changes affecting the process?
Religious and cultural beliefs are having a profound affects on our world. Scientific study could shed new light on the interactions.
I remember SciAm's choice in recently publishing an article challenging the very concept of "hard-wired" human nature in a broadside attack on the relatively new science of Evolutionary Psychology (“The Four Fallacies of Pop Evolutionary Psychology”, Jan. 2009). Now, it has featured, on the cover no less, brand new research revealing that hard-wired human nature, as a scientific concept, is very much "alive and well". Of course, that's the nature of science ---always subject to change.
Reply | Report Abuse | Link to thisYet, why did the editors need to give the article such a grossly misleading title? On the cover, the article is promoted as "Human Evolution Is Not Over: How our species is still changing over time". While the title is technically true, the implication fostered is precisely the opposite of what the research actually shows. The author actually answers the title question with two simple words "...glacially slow ...major adaptive shifts require stable conditions across millennia". Is it so very hard for SciAm to more candidly announce that its prior publication choice in attacking the concept of human hard-wiring, foundational to all Evolutionary Psychology, was in error?
But I guess that's human nature ---even Sci Am editors don't like to eat crow!
As technology enables more and more people to reproduce, it would seem that "bad" genes would be accumulating, e.g. a person born blind might have children with a person born deaf, producing some offspring with both disadvantages. I would like to hear the author's view on this.
Reply | Report Abuse | Link to thisLysenkoism? Social Darwinism? Unless we are evolving into the Borg modern science is preventing Mother Nature from cleaning the gene pool. Modern meds are permitting people to pass on defective DNA to the next generation. How is natural selection supposed to work under these conditions.
Reply | Report Abuse | Link to thisThanks to modern egalitarianism the major evolutionary change we will see in the near future is the disappearance of the recessive "white' characteristic.
Now that birth control pills are available, human
Reply | Report Abuse | Link to thisevolution may be strongly affected by human preferences.
Ideologies will make even more difference than they
have in the past.
John McCarthy
Jonathan Pritchard makes the point that many traits are influenced by hundreds, if not thousands of genes. This concept has been widely known among "practicing evolutionists" (i.e., plant and animal breeders) for many years. Take corn for example; grain yield is the adaptive trait that corn breeders select for. It is thought by many corn breeders that every gene in the corn genome influences grain yield. Years of selection experiments with molecular markers in corn has led to little genetic gain. This is largely because the relationship of individual SNPs to the traits of interest is very low (r < .05). These days, breeders are using so-called genome wide selection in an effort to achieve better gains.
Reply | Report Abuse | Link to thisThe question Pritchad was asked about "are we still evolving" brings up a point that many of us do not think about. Indeed, all populations of organisms evolve and all have progenitors that were less adapted to their environment than those that came later (or even those that existed earlier). Humans have not always existed with our present gene (allele) frequencies. And our descendants far into the future will not have the same gene (allele) frequencies as we do. It may reach a point where our descendants will branch off into other species, and even genera. This may be millions of years into the future, but it could happen. What's the relevant point?
Reply | Report Abuse | Link to thisWe humans often believe we're the penultimate species. Did Pritchard's questioners have that in mind when they asked "are we still evolving?" No one knows the future of course, but one can imagine an Earth inhabited by many species of beings with a much higher level of intelligence than Newton or Einstein or Mendel or Darwin. Maybe even a level of artistic talent that our Mozart's and da Vinci's and Longfellows could only dream of. Or something entirely different.
Don't confuse evolution with Social Darwinism. The theory of evolution does not specify the direction of the change, only that critters will adapt or die off. Social Darwinists are enraptured with the concept of "complexity."
Reply | Report Abuse | Link to thisCockroaches have been around in there present form for millions of years longer than humans and will probably be around after the big nuke war. Cockroaches are more "evolved" than humans.
No confusion here. See my last sentence. "Or something entirely different." Unlike breeding, natural selection is un-directed.
Reply | Report Abuse | Link to thisOn the other hand, I do not think cockroaches are more evolved than anything else. To be evolved is to be adapted to one's environment (on a population basis). Humans, cockroaches, bacteria, etc. are all evolved. Measuring degree of evolvement is a slippery slope. One would have to start with an agreement on what constitutes "more evolved."
John McCarthy made the point that "human evolution may be strongly affected by humans preferences." Of course "assortative mating" occurs in many species, and that's exactly what this is. We usually pick our mates (see the word usually) based on culture, race, interests, and other physical characteristics. Despite the sobriquet that opposites attract, generally that's not true when selecting a mate. Like by like is the general rule of population dynamics. So new technologies, such as being able to pick our offspring's characteristics with genetic markers and having the freedom to do so may not actually change anything (see the words, "may not").
Reply | Report Abuse | Link to thisThank you for your article in SciAm on “How We Are Evolving”. It seems to me that the history of our species from about 24,000 to 37,000 years BP will tell us an awful lot about who we are today and why we act as we do. As you know, science has made all sorts of assumptions about what we were like in Southern France 35,000 years ago. The European invaders of the Americas made similar assumptions about the folks living there for millennia before they arrived. It is helpful that you point out that it is not genetic change that enabled overcoming the environmental challenges our species encountered as we rather suddenly moved around the rest of the world and technology alone does not seem adequate to explain the rapidity with which that expansion occurred. I suggested some time ago at, http://abacus.bates.edu/eclectic/vol2iss1/nonfiction/tierneynonfic.html, that confidence that we could kill the predators, which for millennia, had limited our travel, was the significant variable. Confidence is the other side of fear and once we were confident we could kill the marsupial lion before it tore a child apart in front of our eyes, the rest of the world was our oyster. James Tierney Auburn, ME.
Reply | Report Abuse | Link to thisThe article refers to evolution under the pressure of environment, as in the case of Tibetans, adopting to living at high altitude. Perhaps evolution requires stimulus by way of demands of environment and may be other factors too.
Reply | Report Abuse | Link to thisIs the converse also true? That is, if there is no environmental pressure or other stimulus, does the human evolution slow down or stop? On the other hand, if man continues to tinker with, or tamper with, or modify nature using technological innovation, to suit his needs, can evolution be actually reversed?
Evolution has no direction - so it can't by definition be reversed. On the other hand, humans could actually drive evolution in any direction we want (eugenics). This would be breeding. I doubt there would be much cooperation, though. Also, evolution never stops (until the population dies). There are four forces driving evolution (in the simplest terms and without assigning importance to any one force). These are random mutation, non-random mating (selection), genetic drift, and migration. Only one of these has to occur for evolution to occur. Many of us believe that evolution only involves speciation, but that's not true. Speciation occurs via evolution and by one or more of the four forces driving evolution.
Reply | Report Abuse | Link to thisA small but important error in the article should be corrected: SNPs are not, as suggested in a couple places, alleles. A mutation in a gene that changes its nucleotide sequence produces an allele of the gene. So the SNPs are one cause of the evolution of alleles (there are others, such as InDels), but they are not themselves alleles.
Reply | Report Abuse | Link to thisAbout light skin, allowing a better use of solar light to synthesize D vitamin : I understand from the article that the East Asians and the "WEuropeans" (at large) are getting basically the same favorable effect from a different tuning of genes. Actually, given this example and the global presentation of the article, it seems to me that the limiting factor in human evolution has been (is?) the rate of creation of new favorable sets of genes, not the capacity by nature to select those genes.
Reply | Report Abuse | Link to thisAbout the catalog of traits selected by evolution in human beings, I remember from previous readings that population from one or some pacific islands have an adaptation to seeing underwater. Does somebody knows if that is a scientifically acknowledged fact ?
If modern health care is preventing more and more people from dying, is natural selection being compromised, i.e. are "bad" genes and mutations accumulating in the gene pool?
Reply | Report Abuse | Link to thisSure. Where I live, and probably thoughout the rich world, it appears that birth control may cause humans to gradually get dumber. Successful use of birth control takes brains.
Reply | Report Abuse | Link to thisAre we still evolving? Sure. In fact of all the animals currently existing on this planet we, our domestic organisms and the organisms that have come along for the ride (rats, cockroaches, etc.) are all evolving quite rapidly compared to most of wild organisms.
Also, you can see differences aroung the world. My experience (non-proven)with First Nations (native) people in Western Canada is that they are much more able to handle cold weather than I am or my friends with tropical ancestries. As apposed to the Tibetans, native Americans could not run away and had to put up with weather extremes with fewer tools than we have today.
I wonder, is anyone in this field looking at the correlatition of diet to aspects such as skin colour? I had heard, for instance, that olive-skin colouring could be maintained in human populations with a high fish diet; that is, they were getting their vitamin D from their diets.
A couple more examples of human evolution (again, not proven just speculation) are the athetiticism of African-Americans due to selection for physical strength by slave owners. Also, the higher average intelligences of Ashkenazi Jews (Einstein) - 3% of US population but 27% of nobel prizes. This was possibly due to the selection that occurred by not allowing land ownership and forcing Jews into urban professions and businesses.
Science, math and writing appeared to be easier for people with urban-aqriculture anestries (caucasians and asians).
Thank you CollinBuss. I appreciate your reply. I sense a general reluctance by society to address this, perhaps a fear of violating political correctness.
Reply | Report Abuse | Link to thisThe 2006 movie Idiocracy , while a comidy,is more closer to a documentery and closly addresses this article.
Reply | Report Abuse | Link to thisIn the movie "Jurassic Park," the scientist said, "Life will find a way." The incredible power of the life force is irresistible. It is so powerful it overcomes the environmental challenges. Crush it, blow it up, war, disease, ice ages, life always comes back, it always finds a way.
Reply | Report Abuse | Link to thisI never known there is such an incredible force and unstoppable power of life is what drives each of us each day, what drives our survivals. The power of human life and the expected march forward that the strongest powers of the universe cannot hold back. To my surprise, novel genetic mutations contains natural selection are at a far slow pace. The fact that reveals considerable evidence by this article is “humans are still evolving”, even the rate of change is glacially slow beyond our generation.
I just got around to reading this interesting article the week of Jan 3rd, the point of which I will touch on later.
Reply | Report Abuse | Link to thisPritchard says "But it turns out that although the genome contains some examples of very strong, rapid natural selection, most of the detectable natural selection appears to have occurred at a far slower pace than researchers had envisioned." That may nave been surprising to the researchers but it was a great news to me, I believe I understand this unexpected pattern.
I recently read Bursts by Albert-Laszlo Barabasi, a book I think the author of this article would benefit from reading. Barabasi explains the hidden pattern behind everything we do as a power law that manifests as a burst pattern, short periods of intense activity followed by prolonged periods of inactivity. Barabasi demonstrates how this bursty pattern manifests itself in every facet of life from how we email to how we read internet articles, which is why I mentioned that I just read an article that had been out for months. Burstiness is evident in how currency moves around as well as how life migrates, which is discussed in this article as well.
In this book, Barabasi states that evolution proceeds in bursts and I was seeking a real world, real time example and I believe this may be it.
The really intriguing prediction is that according to Barabasi bursts are deeply linked to human will and intelligence. Additionally the data suggests that bursts require the ability to set priorities. So if the recent findings in this article unearth an unexpected pattern of evolution that can be explained as a burst pattern power law, then the human genome has the ability to set priorities. This is, of course, discussed to some degree in this article by Pritchard when he explains how a SNPs and alleles move forward, the genome itself decides and regardless of the biological mechanics behind that process the genome must still have the ability to prioritize. Fascinating.
I don't comment on things like this very often but if you found this an interesting discussion please let me know.
Thanks for reading!