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Creationism/Evolution Title: Early humans had sex with chimps Our early ancestors interbred with chimpanzees after the two species drew apart millions of years ago, a new paper suggests. The provocative idea is sketched by US genome experts, who have discovered that hominids and chimps diverged far more recently, and over a much longer timescale, than anyone had thought. During this time, the authors theorise, the two primates were rather more than kissing cousins: they had sex, swapping genes before making a final separation. "The ... analysis revealed big surprises, with major implications for human evolution," says Professor Eric Lander, director of the Broad Institute of Harvard University and the Massachusetts Institute of Technology, and co-author of the paper in today's issue of the journal Nature. Until now, the belief was that humans and chimpanzees shared a common ancestor but went their separate ways around 6.5-7.4 million years ago. The basis for this is a carbon-dated fossil called Toumai, whose supporters say is the oldest known human. Its critics, though, dismiss Toumai as an ape. The estimate is also backed by the molecular clock, a method of calculating evolution on the basis of the speed at which genes mutate. Previous molecular-clock studies have focused on the average genetic difference between human and chimp. But the new paper takes a different approach. Looking at DNA Exploiting the mountain of data that has come from the human and chimpanzee genome projects, the researchers compared the genetic codes of the two species as they are today. They then estimated the various age of key sequences, rather than the overall average. They believe that the two species made their split no later than 6.3 million years ago and probably less than 5.4 million years ago. In other words, around 1 to 2 million years earlier than the Toumai estimate. Moreover, speciation of chimp and hominid, the process by which they emerged as separate species, took an extraordinary long time: around four million years in all. The youngest chromosome in the human genome is the X, which helps determine gender. On average, X is around 1.2 million years more recent than the 22 non-sex chromosomes, the scientists found. Lander describes X's tender age as "an evolutionary 'smoking gun'". Sex chromososmes Previous studies suggest that sex chromosomes are among the most vulnerable of chromosomes when it comes to interbreeding. This is because co-mingling places its genes under swift selective pressure. Thus something unusual must have happened on the way to speciation: an initial split between human and chimp, followed by interbreeding, whose results show up in progressive younger genes, and then a final separation. Lead author Dr Nick Patterson, also at the Broad Institute, says that Toumai's claimed status as humans' ancestor has been somewhat clouded. "It is possible that the Toumai fossil is more recent than previously thought. But if the dating is correct, [it] would precede the human- chimp split," he says. "The fact that it has human-like features suggest that human-chimp speciation may have occurred over a long period with episodes of hybridisation [inter-breeding] between the emerging species." A gradual divergence of species through hybridisation, rather than a quick break, may be far more common than we suspect. "That such evolutionary events have not been seen more often in animal species may simply be due to the fact that we have not been looking for them," says the team's senior author, Assistant Professor David Reich, also of the Broad Institute. Post Comment Private Reply Ignore Thread Top • Page Up • Full Thread • Page Down • Bottom/Latest Begin Trace Mode for Comment # 1.
#1. To: Vicomte13 (#0)
Considering your expertise on this subject. Can you give us any insight?
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