Is Africa the cradle of humanity?
by Robert Lamb
Publicado en 2007 en http://science.howstuffworks.com/life/evolution/africa-cradle-humanity1.htm
|A Masai warrior surveys the landscape of the Lewa Wildlife Conservancy in Kenya, one of the oldest areas of human occupation. Joe Sohm/Digital Vision/Getty Images|
Out of Africa Theory
If you look hard enough, you'll find any number of theories about just where human beings originated -- and who knows? Maybe we really were banished from a Mesopotamian Garden of Eden, or we really did stumble out of a crashed spaceship. The prevailing theory among scientists, however, is that the first Homo sapiensevolved in Africa and, between 56,000 and 200,000 years ago, migrated into other lands.
Some anthropologists actually refer to this theory as the out of Africa II theory, as it involves a previous African exodus by tribes of Homo erectus, followed by the scattering of H. sapiens that eventually became human civilization. This wave of migration steadily washed over the entire world for tens of thousands of years. The pockets of primitive hominids, such as Neanderthals, eventually disappeared. Perhaps they weren't able to compete with H. sapiens for limited resources or weren't as capable of adapting to survive the constant rigors of a prehistoric Earth.
Studies continue to back up the out of Africa theory. In studying the genetic diversity and skull shapes of 53 human populations from around the world, a team of Cambridge researchers discovered interesting proof to support the idea. They found that the farther the population was from Africa, the less varied its genetic makeup. The reason being that, as humans spread out from the cradle of civilization, their population sizes dropped. That also meant there was less genetic diversity to go around.
Think of it in terms of a group of friends getting together for a night out after work on Friday. The later it gets, the more people drop out. By 1 a.m., the group of revelers is much smaller, encompassing far less diversity.