A new analysis of DNA evidence offers proof that modern humans interbred with other populations around the world for hundreds of thousands of years rather than replacing them. This means that the genes of people today carry vestiges of the genes of Neanderthals and other extinct branches of the human family.
According to the original Out of Africa theory, the ancestors of today?s human population migrated from Africa 100,000 years ago, and they replaced less modern populations living in Europe and Asia.
The new study by population biologist Alan R. Templeton of Washington University suggests instead that there were at least two distinct migrations. The first wave occurred between 420,000 and 840,000 years ago, and the second between 80,000 and 150,000 years ago. Each time, they interbred with the more primitive humans they encountered.
Templeton has developed a computer program called GEODIS to analyze genetic material taken from thousands of present-day humans around the world. His model analyzes DNA from 10 locations in each genetic sample. Previous statistical models have targeted just one region of DNA, for example the mitochondrial DNA that is passed down from the mother. This narrow approach results in incomplete results ?with low statistical resolution,? says Templeton.
This will help answer a question that scientists have been trying to figure out for years: What happened to the Neanderthals? Were they physically conquered by modern humans or simply outwitted by them? According to Templeton, they interbred with the more modern humans coming out of Africa and produced a new race of people?our ancestors.
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Jewelry made by prehistoric people is shedding new light on the debate over the origin of modern humans. Ornaments that existed at the same time as changes in hunting practices, at widely dispersed sites across Europe and Asia, suggests that modern human behaviors arose simultaneously in many places.
This provides evidence for the theory of modern human development occurred at the same time in different populations across the world, suggesting the integration of natives with incoming Africans. The alternative ?out of Africa? theory suggests that an invasion about 50,000 years ago drove native populations to extinction.
Mary Stiner, of the University of Arizona, says that the earliest examples of jewelry and other adornment occur close in time in at least four different places. She has uncovered shells in Turkey that were punctured in a deliberate way between 40,000 and 45,000 years ago. These holes, for stringing the shells like beads, could not have been made by accident, she says. Ostrich eggshell beads from the same period have also been made in Kenya, and other adornments have been unearthed in Lebanon and Bulgaria.
Further investigation by Stiner and her colleague Steven Kuhn in several Upper Paleolithic sites around the Mediterranean has revealed a change in the prey hunted by early humans in the east about 40,000 to 50,000 years ago. Stiner says there are also early indications of similar changes in Africa. Their analysis shows there was a shift from hunting slow-reproducing and easy-to-catch animals like shellfish and tortoises, to quickly-reproducing and more agile animals like partridges, hares, and rabbits. This was probably caused by increased pressure on resources, due to over-hunting and increased population. Stiner says, ?If you have over-used your preferred resource, you can respond by turning to lower-ranked, harder-to-catch resources.?
An increasing population may also explain the use of ornaments, because of the increased need to communicate with each other. ?Ornamentation is universal among all modern human foragers,? says Stiner. These two behavioral changes occurred long after the first appearance of anatomically modern humans in the fossil record.
Archaeologist Lawrence Straus, of the University of New Mexico, says the jewelry and hunting evidence supports the continuity theory. He says, ?The ongoing process of human adaptation was a long, drawn out process, mosaic in nature. The idea of a total and abrupt replacement of an inferior species 40,000 years ago has in my opinion been fabricated.?
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