The Georgian skull discovery explained - in 90 seconds
18 October 2013 Last updated at 22:53 BST
The idea that there were several different human species walking the Earth two million years ago is being called into question.
Scientists in Georgia studying the largest set of complete primitive human remains believe there was only one human species, which displayed more variety than previously thought.
BBC News explains the background in 90 seconds.
Video Producer: Dougal Shaw
Images Courtesy Georgian National Museum