STRANGE ISOLATION..
In Mexico, skulls from three areas were analyzed, dating back 500 to 800 years. The Sonora and Tlanepantla heads shared similarities but not those from Michoacan.The measurements were so different that they resembled a group that had developed in isolation for thousands of years. Yet no unbreachable landscape separated the regions. Michoacan was also just 300 kilometers (186 mi) away from Tlanepantla. For some reason, the Michoacan group did not interbreed with their neighbors and developed a distinctive skull shape.Researchers turned to human remains dating as far back as 10,000 years when Mexico received its first influx of people. These skulls came from Lagoa Santa and revealed something astonishing.[1]They, too, were so different that 10,000 years was not enough time to have evolved the skull features of South Americans today. The Lagoa Santa skulls likely shared an ancestor with modern South Americans but split 20,000 years ago outside the Americas.Conventionally, a single wave was thought to have settled the Americas. Several migrations from different areas make more sense. People isolated by tough language and cultural barriers offer some explanation for the Michoacan group. But why they remained genetically exclusive for millennia is not entirely understood.