Evolution in Your FaceLake Victoria, Africa's largest lake, is home to more than 300 species of cichlids. These fish, which are popular in aquariums, are deep-bodied and have one nostril, rather than the usual two, on each side of the head. Seismic profiles and cores of the lake taken by a team headed by Thomas C. Johnson of the University of Minnesota, reveal that the lake dried up completely about 12,400 years ago. This means that the rate of speciation of cichlid fishes has been extremely rapid: something on average of one new species every 40 years!
by Patrick Huyghe
Omni
The core samples brought them face to face with the incredible history of Lake Victoria and a discovery that would shatter a world record in the rate of species evolution.
“We broke the pipe apart and saw grass and other evidence to suggest we had actually penetrated through to a soil horizon. It implied that indeed this soil had at some point come into contact with air!” Johnson said. “Grass, however, is not a definite indicator of exposure to air because it can easily be carried by currents out onto the lake where it would sink into the sediment.”
As the team continued the coring technique, they kept finding hard sediment layers and evidence of grass.
“We moved to different sites on the lake and found the same evidence. We took core samples eight times and the same thing came up time and time again,” Johnson said.
By this time Johnson said they could not deny what they discovered on their geological expedition of Lake Victoria. The implications would make news in the world of evolutionary science.
The team didn't have sophisticated testing equipment on the ship to analyze the sediment, so they waited for verification from the samples shipped to the University of Minnesota's Limnological Research Center in Minneapolis. Back in Minnesota, Johnson and his colleagues from the Limnological Research Center, the University of Bergan, Norway, and Materera University, Uganda, found evidence that confirmed their suspicions. They found that Lake Victoria had completely dried out 12,000 years ago.
“We found grassland soil and clay with cracks in it showing that the lake had dried out,” Johnson said, “and there was pollen from cattails just overlying the soil, suggesting a marsh-like setting as the lake basin began to refill.”