Evolutionary Timeline of Modern Human Traits Linked to Changing Environment

Humans were thought to have evolved into the modern creatures we know today between 2.4 and 1.8 million years ago in Africa. While scientists have recognized these modern characteristics for decades, though, they are now reconsidering the true evolutionary factors that drove them.

As Earth's climate became cooler and driver, researchers believed that humans evolved a large brain, long legs, the ability to craft tools and prolonged maturation periods. In fact, researchers believed that these traits all emerged at once-relatively speaking. Yet now, scientists have announced that these traits did not arise as a single package. Instead, several key ingredients evolved in earlier ancestors.

The researchers used archaeological remains and biological studies of a wide range of mammals, including humans. More specifically, they looked at five skulls about 1.8 million years old from a site in the Republic of Congo. These skulls showed traits that varied from those typically seen in African H. erectus but differed from defining traits of other species of early Homo. This allowed them to determine that the ability of early humans to adjust to changing conditions ultimately enabled the earliest species of Homo to vary, survive and begin spreading from Africa about 1.85 million years ago.

"Unstable climate conditions favored the evolution of the roots of human flexibility in our ancestors," said Richard Potts, one of the researchers, in a news release. "The narrative of human evolution that arises from our analyses stress the importance of adaptability to changing environments, rather than adaptation to any one environment, in the early success of the genus Homo."

It's possible that early species of Homo actually divvied up the environment with each using slightly different strategies to survive. This would help explain the trait variations. This, in turn, suggests that the package of modern, human traits evolved separately and at different times rather than all at once. This flexibility allowed ancient human ancestors to successful adapt to unstable environments and disperse from Africa.

The findings are published in the journal Science.