TUCSON, Oct. 10 (UPI) -- A U.S. study suggests ancient African megadroughts might have driven the evolution of humans and fish during the late Pleistocene era.

The research, led by Professor Andrew Cohen of the University of Arizona-Tucson, suggested that from 135,000 to 90,000 years ago, tropical Africa had megadroughts more extreme and widespread than any previously known for that region.

"Lake Malawi, one of the deepest lakes in the world, acts as a rain gauge," said Cohen. "The lake level dropped at least 600 meters (1,968 feet) -- an extraordinary amount of water lost from the lake. This tells us that it was much drier at that time."

Cohen said the finding provides an ecological explanation for the hypothesis that all humans descended from just a few people living in Africa sometime between 150,000 and 70,000 years ago.

"We've got an explanation for why that might have occurred -- tropical Africa was extraordinarily dry about 100,000 years ago," said Cohen. "Maybe human populations just crashed."

Two studies by Cohen are to appear in the Proceedings of the National Academy of Sciences.