[EMAIL PROTECTED] Study finds humans still evolving, and quickly
> URL to a very interesting article in LA Times > _http://www.latimes.com/news/science/la-sci-evolution11dec11,0,5882337.story_ > (http://www.latimes.com/news/science/la-sci-evolution11dec11,0,5882337.story) > > I thought that after humans learned to control their environment they > would > basically stop evolving, but it seems I'm wrong > > First few paragraphs > " > By Karen Kaplan, Los Angeles Times Staff Writer > December 11, 2007 > 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 historical 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 pressure 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 time. > > 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 the genes remains a mystery, said > University of Wisconsin-Madison anthropologist John Hawks, who led the > study. But > the research team was able to conclude that infectious diseases and the > introduction of new foods were the primary reasons that some genes swept > through > populations with such speed. > > "If there were not a mismatch between the population and the environment, > there wouldn't be any selection," Hawks said. "Dietary changes, disease > changes > -- those create circumstances where selection can happen." > > One of the most famous examples is the spread of a gene that allows > adults > to digest milk. > > Though children were able to drink milk, they typically developed lactose > intolerance as they grew up. But after cattle and goats were domesticated > in > Europe and yaks and mares were domesticated in Asia, adults with a > mutation > that allowed them to digest milk had a nutritional advantage over those > without. > > As a result, they were more likely to have healthy offspring, prompting > the > mutation to spread, Hawks said. > > The mechanism also explains why genetic resistance to malaria has spread > among Africans -- who live where disease-carrying mosquitoes are > prevalent -- > but not among Europeans or Asians. > > 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 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." >
