Re: Evolution. Yes? or No?
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Originally Posted by Xolo
Mutations occur about once every 32,000 years or so. Man has been in the works for 5 million years. That's a lot of mutations. Beyond my ability to figure out without a calculator.
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What is your source for the 32,000 year time period? It doesn't correlate with any other information I am aware of.
Quote:
Originally Posted by Xolo
We are all 99.99% African, except with a few recessives where Africans have dominants hiding their recessives.
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Frankly, I find that of little importance or significance. Humans are not the sum total of their genetic code unless one believe he is a slave to it.
Here's a couple of excerpts from internet sources some here may find interesting reading:
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Although the study of natural selection in humans is still in an early stage, the new data, building on decades of earlier work, are beginning to reveal some of the landscape of selection in our species. In fact, researchers have identified many genetic loci at which selection has likely occurred, and some of the selective pressures involved have been elucidated. Three significant forces that have been identified thus far include changes in diet, changes in climate, and infectious disease.
Lactose Tolerance
The domestication of plants and animals roughly 10,000 years ago profoundly changed human diets, and it gave those individuals who could best digest the new foods a selective advantage. The best understood of these adaptations is lactose tolerance (Sabeti et al., 2006; Bersaglieri et al., 2004). The ability to digest lactose, a sugar found in milk, usually disappears before adulthood in mammals, and the same is true in most human populations. However, for some people, including a large fraction of individuals of European descent, the ability to break down lactose persists because of a mutation in the lactase gene (LCT). This suggests that the allele became common in Europe because of increased nutrition from cow's milk, which became available after the domestication of cattle. This hypothesis was eventually confirmed by Todd Bersaglieri and his colleagues, who demonstrated that the lactase persistence allele is common in Europeans (nearly 80% of people of European descent carry this allele), and it has evidence of a selective sweep spanning roughly 1 million base pairs (1 megabase). Indeed, lactose tolerance is one of the strongest signals of selection seen anywhere in the genome. Sarah Tishkoff and colleagues subsequently found a distinct LCT mutation also conferring lactose tolerance, in this case in African pastoralist populations, suggesting the action of convergent evolution (Tishkoff et al., 2007).
Pigmentation
As proto-Europeans and Asians moved northward out of Africa, they experienced less sunlight and colder temperature, new environmental forces that exerted selective pressure on the migrants. Exactly why reduced sunlight should be a potent selective force is still debated, but it has become clear that humans have experienced positive selection at numerous genes to finely tune the amount of skin pigment they produce, depending on the amount of sunlight exposure.
The role of selection in controlling human pigmentation is not a new idea; in fact, it was first advanced by William Wells in 1813, long before Darwin's formulation of natural selection (Wells, 1818). In recent years, signals of positive selection have been identified in many genes, with some signals solely in Europeans, some solely in Asians, and some shared across both continents (Lao et al., 2007; McEvoy et al., 2006; Williamson et al., 2007). Evidence for purifying selection has also been found to maintain dark skin color in Africa, where sunlight exposure is great.
A good example of selection for lighter pigmentation is the gene SLC24A5, which was one of the first to be characterized. Rebecca Lamason and her colleagues identified a mutation in the zebrafish homologue of this gene that is responsible for pigmentation phenotype. The investigators then demonstrated that a human variant in the gene explains roughly one-third of the variation in pigmentation between Europeans and West Africans, and that the European variant had likely been a target of selection (Lamason et al., 2005). In related work, Angela Hancock and her colleagues examined many genes involved in metabolism, and they showed that alleles of these genes show evidence of positive selection and correlate strongly with climate, suggesting that humans adapted to cooler climates by changing their metabolic rates (Hancock et al., 2008).
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Evolutionary Adaptation and Positive Selection in Humans | Learn Science at Scitable
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Geneticists at Stanford now have laid this question to rest. Their results, scheduled to be published Jan. 16 online in Public Library of Science Genetics, show adaptation-the process by which organisms change to better fit their environment-is indeed a large part of human genomic evolution.
"Others have looked for the signal of widespread adaptation and couldn't find it. Now we've used a lot more data and did a lot of work cleaning it up," said Dmitri Petrov, associate professor of biology at Stanford University and one of two senior authors of the paper. "We were able to detect the adaptation signatures quite clearly, and they have the characteristic shape we anticipated."
All genetic mutations start out random, but those that are beneficial to an organism's success in their environment are directly selected for and quickly perpetuate throughout the population, providing a uniform, traceable signature.
With the help of post-doctoral researcher James Cai and recent graduate student Michael Macpherson, Petrov and co-senior author Guy Sella, a biologist at the Hebrew University of Jerusalem, used different methodology from what's been used before to look for signatures of adaptation left in the human genome.
"We detected a number of signatures that suggest adaptation is quite pervasive and common," Petrov said.
Humans have a very complex history from traveling around the globe, and the human genome is also highly structured, making it complicated and difficult to work with, he said.
To find the adaptation signal, Petrov and his colleagues looked for regions of the genome that "hitchhiked" along with an adaptation. When a genetic adaptation occurs and is passed on to offspring, other genes on both sides of the adaptation typically accompany it. The result is a whole region of the genome where all humans are unusually similar to each other, referred to as a "selective sweep," that researchers can identify and trace through human genetic history.
"Adaptation becomes widespread in the population very quickly," Petrov said. "Whereas neutral random mutation doesn't and would not have the selective sweep signature."
"We tried to see if these regions of unusual similarity among all humans tended to be in particular places in the genome as the theory predicts they should be, and indeed we find them there," Petrov said. "The work suggests human beings have undergone rampant adaptation to their environment in the last 200,000 years of history."
In the past, these sweeps were difficult to discern because the data were not sufficiently abundant and were filled with noise. Depending on the methodology, estimates of the degree of adaptation in humans ranged from as high as 30 percent down to zero. Signatures were impossible to interpret with confidence.
"People would find changes in specific genes suggesting that recent adaptations in humans might be common but could not find genome-wide signatures of pervasive adaptation. That was unsettling," Petrov said. "I'm hoping that people will react with relief that things are starting to make sense."
Petrov hopes that researchers can now do a much better job of finding the regions within the genome responsible for specific human adaptations and relate them to changes in human history or past environments. For example, one could trace the arrival of lactose tolerance to the domestication of cattle and the introduction of milk into our adult diet.
"As the data are going to grow, we should be able to locate specific adaptive events quite well," Petrov said. "By identifying specific genes, we can unravel this evolutionary history of adaptive change."
Another possibility is tracing the origin of skin pigmentation genes, which give people their different skin-color types. Many of these genes are linked to skin cancer. Researchers may be able to recreate past environments while better understanding how adaptation comes into play.
"We see signatures of possibly hundreds of recent adaptive events, and now we can ask what are they doing there," he said. "It's both exiting and puzzling."
This paper follows similar work in bacteria and fruit flies indicating adaptation is a significant contribution to evolution as a whole.
"We are on a crest of a wave showing that adaptation is a lot more prevalent than we thought," Petrov said
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Adaptation Plays Significant Role In Human Evolution
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03-15-2011, 01:03 PM
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