This link has been bookmarked by 20 people . It was first bookmarked on 07 Oct 2008, by Rudy Garns.
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08 Feb 09
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18 Dec 08
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When the previous generation of life scientists was coming up through the academy, there was a widespread assumption, not always articulated by professors, that human evolution had all but stopped. It had certainly shaped our prehuman ancestors — Australopithecus, Paranthropus, and the rest of the ape-men and man-apes in our bushy lineage — but once Homo sapiens developed agriculture and language, it was thought, we stopped changing. It was as though, having achieved its aim by the seventh day, evolution rested. "That was the stereotype that I learned," says population geneticist and anthropologist Henry Harpending. "We showed up 45,000 years ago and haven't changed since then."
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Moreover, evolution had never been observed in humans, except in a few odd cases, so the conclusion was drawn that it wasn't happening. One can't fault the logic. The most famous case of adaptive change in humans, that of sickle cell trait as an evolutionary response to malaria, seemed to prove the point that human evolution must be rare: Even in as dire and malaria-stricken an environment as West Africa, the only response evolution has been able to come up with is an imperfect defense that can cause serious health problems along with its solitary benefit. Selection pressures as strong as those brought about by endemic malaria are uncommon, and civilization was thought to wash out those less powerful.
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By looking at the data from HapMap, a massive survey of the genetic differences between selected populations from around the world, Hawks identified gene variants, or alleles, that were present in many people's DNA, but not in everyone's. These alleles seemed to be moving, over time, through populations in a way that matched mathematical predictions of what natural selection should look like on the genomic level. And though Hawks doesn't know why possession of the new alleles should be advantageous, he doesn't need to know. The signature that natural selection inscribes on the genome is legible even when the import of the message is unclear.
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One of the characteristics of this linkage is that it is strong over short distances on a chromosome and weak over long distances. This is because mutations are rare but equally likely at every location, so they happen less often in a small region of DNA than in a large region. Over many generations, mutations nibble away at the edges of haplotypes and poke holes in their interiors, and the routine reshuffling of nucleotides, called recombination, can move linked sections of DNA far from one another, thereby breaking the linkage. Thus, the length of a haplotype roughly indicates its age, as does the amount of variation within it. Since mutations and recombination occur at a predictable rate, by comparing haplotypes from two populations, one can determine their degree of relatedness and thus estimate how long ago they diverged. So, for example, the San of southern Africa and the Han Chinese, would tend not to share haplotypes because their populations diverged long ago, and those they did share would be short or contain a great deal of variation.
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An oft-cited example of evolution in historic times is the spread of the mutation that allows humans to digest milk in adulthood. It seems to have arisen around 8,000 years ago and has since spread to all parts of the world, though there are still plenty of us without it: One in 50 Swedes and nine out of 10 Asian Americans lack the mutation. The lactose intolerant are, at least in this respect, as the first Homo sapiens were.
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There are five versions of the lactase drinking gene, so five different populations have mutations that let them drink milk," says Hawks. Because of this, many mutations conferring the same benefit are unlikely to have become common by genetic drift, but Hawks knows of practicing geneticists who find the idea that natural selection was the agent of their propagation to be preposterous. He's
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"The biggest change in our lifestyle as a species has happened in the past 10,000 years," Wells says. "We spent most of the past million or so years of evolution living as hunter-gatherers, hunting game on the African savannas, or gathering shellfish on the coast, gradually moving out to Eurasia. Then, suddenly, in the past 10,000 years, we become a species that settles down. The diversity of food sources drops precipitously from over 100 in the hunter-gatherer diet to fewer than 10 in the average agricultural diet. And then, of course, you build up the population densities and disease takes off."
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Pardis Sabeti, an evolutionary geneticist at MIT's Broad Institute who has done a great deal of work on methods for assessing genomic surveys like HapMap, the first draft of which was published in 2005. HapMap is a leaner and in some ways more powerful version of the Human Genome Project, as it compiles only those regions of the human genome — less than 1 percent — that have the potential to differ from person to person. In comparing different populations' genetic information, it's possible to tease out patterns of gene inheritance, how certain genes correlate with certain diseases, and even the likely geographic origin of some mutations.
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"Some interpret it as meaning, this is the civilization gene, which is clearly not what we're trying to say. Maybe we should have said it with more qualifications, to avoid the misconception," he says. The
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The second face of Homo sapiens' eventual exit from history is the more hopeful possibility that we may yet evolve into our own successors. Unlike our forebears, we are aware of evolution, which changes our relationship to it, if only by a little, for we are still natural creatures. We continue to evolve, in the face of hunger, disease and a changing ecosystem; but our virtual habitat of culture could enable us to become both subjects of evolution and conscious co-directors of it. "It's occurring," says Ehrlich. "There's no question about it. What's frightening is the questions we'll have to ask."
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Science must evolve new tools to raise us to such a commanding vantage, as well as to avert a self-inflicted extinction. Technology might some day enable us to control aspects of evolution, or it may prove to be the ultimate selection regime, culling all of us. Perhaps we already find ourselves wishing we'd lacked the intelligence to monkey with howitzers. Either way, the culture that we've created is, strangely, evolution's most powerful tool and its potential nemesis, the womb of human nature and perhaps its grave. By our own hand: this is how we evolve.
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28 Oct 08
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25 Oct 08
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22 Oct 08
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Rotem HermonA growing number of scientists argue that human culture itself has become the foremost agent of biological change
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Up to 10 percent of the human genome appears to be evolving at the maximum rate, more quickly than ever before in human history.
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15 Oct 08
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14 Oct 08
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12 Oct 08
Harpending and a host of researchers have discovered in our DNA evidence that culture, far from halting evolution, appears to accelerate it.
human genome evolution map HapMap model intelligence culture complexity climate_crisis
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The signature that natural selection inscribes on the genome is legible even when the import of the message is unclear.
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Fisher, a Brit, argued that, in fact, a large population was required, because only a large population can produce large numbers of mutations. Because most mutations are neutral, he reasoned, it takes a large number of mutations to produce one beneficial allele. American biologists were most influenced by Wright, but Fisher's work is where Hawks and Harpending find their support.
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HapMap is a leaner and in some ways more powerful version of the Human Genome Project, as it compiles only those regions of the human genome — less than 1 percent — that have the potential to differ from person to person. In comparing different populations' genetic information, it's possible to tease out patterns of gene inheritance, how certain genes correlate with certain diseases, and even the likely geographic origin of some mutations.
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Is intelligence still being selected for? Parsimony and uniformitarianism would compel one to answer yes; things in the present are, by and large, as they were in the past. But the way evolution works, whereby mutations arise in one person and slowly spread throughout a population, makes such a question difficult to frame, for if intelligence is still under selection, that could mean that some populations at this very moment are slightly smarter than others — that, perhaps, even certain ethnicities are slightly smarter than others. In the West, speculation on the subject almost automatically tars the speculator as a eugenicist or a racialist.
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"Intelligence builds on top of intelligence," says Lahn. "[Culture] creates a stringent selection regime for enhanced intelligence. This is a positive feedback loop, I would think." Increasing intelligence increases the complexity of culture, which pressures intelligence levels to rise, which creates a more complex culture, and so on. Culture is not an escape from conditioning environments. It is an environment of a different kind.
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"The fate of our civilization, and maybe our species," says Ehrlich, "may be determined by the next five generations. So I don't really give a shit what's happening to our genetic evolution." The global climate is changing too violently for DNA to respond by fiddling around with heat regulation and hair thickness; forests everywhere are being clear-cut too quickly for their inhabitants to adjust, and so food chains are coming undone; the collapse of global fisheries has been identified as an imminent calamity; and a nuclear disaster would constitute a catastrophe many orders of magnitude larger than what nature could readily absorb. If any of these nightmare scenarios comes to pass, Ehrlich fears, evolution will be unable to help us. It may be operating faster than we thought, but it's not that fast. Problems like smog and acid rain seem almost quaint, and even to be longed for.
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11 Oct 08
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07 Oct 08
Rudy GarnsA growing number of scientists argue that human culture itself has become the foremost agent of biological change. (Seed)
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