- The San of Southern Africa Were Among Those Once Genetically Isolated - Image Ian Beatty
It is generally accepted that modern humans first evolved in east Africa, slowly spread outward as a single species, and colonized most of the planet over thousands of years. But an examination of the mitochondrial DNA of modern African populations provides a tantalizing clue that the real story may not have been quite so straightforward. It seems possible that at some point about 150,000 years ago, the human lineage almost split into two separate species.
The Human Genographic Project
The mitochondrial DNA analysis was conducted by a team including Doron Behar of the Rambam Medical Center in Israel and Dr. Spencer Wells, head of the Human Genographic Project. They examined the mDNA of modern people from different regions of Africa. This choice was based on the natural place where Homo sapiens first evolved and where many humans are still confined when the suspected separation occurred.
Population Split
Though modern Africans are genetically a single population, evidence of a long-ago split appeared in the mDNA of people from different regions of Africa. People from East and West Africa, as well as people outside of Africa who were originally descended from these populations, once were isolated temporarily from people in the southern regions of the continent (e.g., the Khoisan hunter-gatherers).
This separation occurred at some point around 100,000 to 150,000 years ago and may have lasted for as long as 100,000 years. This period of time is the longest known time that two populations of humans evolved separately from one another. Had this separation of populations continued, it is possible, or even likely, that humans eventually could have branched off into two separate species.
Climate Change
The reasons for the population split are not entirely clear, although analysis of climate data from the time suggests a period of extreme drought in east Africa about 135,000 to 90,000 years ago. This ancient period of drought may have driven some humans into the southern part of the continent and eventually isolated them from their counterparts father north.
Species Reunited
The population split, while lengthy, was obviously not permanent. Genetic evidence suggests that the isolated populations began to recombine about 40,000 years ago during the late Stone Age, when climate conditions possibly improved and permitted more population growth and easier migration.
While some other scientists have pointed out that it is still too early to know for certain if the mDNA evidence conclusively demonstrates a split, the findings support other analyses of early human genetics that suggest a bottleneck — where the human population may have shrunk to as few as 2,000 individuals — at a similar point in the history of the human lineage.
Source:
Rincon, Paul. "Human Line 'Nearly Split in Two'" BBC News. 24 Apr. 2008. Web. 06 July 2011. .
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
