The belief that humans are biologically divided into sub-species, which correspond with our definitions of "race" is no longer accepted in the scientific community. All living humans today are of the same biological species. The scientific definition of a biological species is a group of populations that can mate and reproduce successfully within the same group. Since humans of different races can mate and reproduce successfully, all humans are part of the same species. Scientific advances—such as understanding DNA’s double helix structure, Sanger sequencing, and the human genome project—have allowed scientists to better examine our human roots and conclude that "race" is not a viable biological variable in explaining human difference. Rather, geography, human migration, and mutations at the DNA level explain how different people have darker or lighter skin, blue or brown eyes, etc. For example, scientists found that all living humans today are descended from Africa. In the 1900s, the "multi-regionalism" hypothesis—the idea that different races developed from ape-like ancestors in different regions of the world—was used to explain the origin of human races. Population scientists have since debunked the "multi-regionalism" hypothesis. For example, geneticist Brian Sykes (2001) traced mitochondrial DNA sequences from all over the world and found that all modern humans can trace their ancestry to one woman who lived in Africa about 150,000 years ago. Several other studies found that the ancestors of all modern humans came from Africa.
[P1] Scientific studies describe the physical world as it is.