Early humans evolved in fits and starts due to rapid environmental changes—not gradually as scientists used to think, according to a new study. Analyzing lake sediments in northern Tanzania, scientists from Penn State and Rutgers University concluded that climate change altered the landscape back and forth from grassland to woodland five or six times over 200,000 years, the Telegraph reports. That would have changed food availability, diet, and means of acquiring food—which "can trigger evolutionary mechanisms," says Penn State professor Katherine Freeman.
"The result can be increased brain size and cognition, changes in locomotion and even social changes—how you interact with others in a group." Several factors may have triggered the climate changes about 2 million years ago, including changes in sea temperature and the Earth's movement around the sun. Any change in the amount of sunshine, for example, would have altered rain patterns that in turn affected plant patterns. "The research points to the importance of water in an arid landscape like Africa," says a graduate student on the project. The findings conflict with the "Great Drying," the view that Africa gradually dried out over 3 million years.