Until now it was believed that the number of people who chose to leave their African homeland was relatively small and homogenous. Consequently, their descendants in new lands would have lacked genetic diversity since their ancestors all came from a genetically limited population base. Whatever genetic diversity they did possess would decline noticeably over time, as the original migrants divided up into separate groups that mixed with each other less and less.
This theory was developed to explain the results elicited from the existing human fossil record. DNA samples taken from ancient skeletons recovered in various locations in Europe and Asia have shown a low level of diversity, in comparison to ancient skeletons recovered in Africa. But there was a flaw in this research. The human fossils analyzed previously were not as old as the skull recovered from the cave in Romania.