Prior research has found that the Great Rift Valley has experienced great changes over the past couple of million years. Because of its unique geography, the area has been particularly sensitive to changes in temperature and rainfall amounts. During periods of abundant rainfall, huge lakes formed along with lush vegetation—times of less rain saw lakes dry up and deserts creep in making life difficult for those that lived in the area. Shultz and Maslin suggest it was the severe changes in the local environment that tested the brains of the creatures that would eventually evolve to become modern man, causing an increase in size and complexity.
To find out if they were on to something, the two researchers studied data obtained through years of research on the evolution of our planet, focusing specifically on East Africa. They found that wet and dry times in the Great Rift Valley could be marked on a timeline which could be compared with similar timelines created by those that study the evolution of man. In so doing, they found what appeared to be a correlation—brain size seemed to grow during times of change, apparently, as a means of adapting to changing circumstances. More specifically, they found that hominin diversity appeared to peak in the valley just under two million years ago, a period of time that coincides with very large lake size. It also marked the first known appearance of the class of hominins known as Homo, most notably Homo erectus. Similar changes in human evolution were found to align with periods of change in the valley that eventually led to our human ancestors leaving the valley altogether, heading both north and south, presumably, looking for a more stable environment.
Read more at: Phys.org