Alice Roy, a professor at the University of Illinois at Chicago, says that what the new data tell us is that what looks like a “natural transition” isn’t really “natural” at all. Humans aren’t the only ones to have altered the landscape, and it may be that even human beings aren’t the only ones to have left traces on the earth.

“The only natural thing would be to say that something was fundamentally changing,” Roy says.

There are more than 60,000 species on earth—about 30,000 of those are known to researchers as newbie species—most known to life on earth today. Scientists from the U.S. Geological Survey estimate there could be as many as 140,000 new species that haven’t been discovered. These new species are not necessarily the ones we normally call newbie species. In fact, Roy says she’s heard people call these “prehistoric species”—they’ve lived on earth for hundreds of millions of years and may still be around.

Scientists were quick to draw conclusions from the new data on the amount of time it has taken for various species to evolve. The data showed that it took a full 2.23 million years for the common house cat to reach the size it is today. “That long time implies that humans were around for a long time to change it,” she says.

Roy’s research shows that the amount of time between humans moving to the Americas and the arrival of animals on the land probably wasn’t quite 20,000 years—more like 50,000–100,000 years, she says. In fact, some scientists think the amount of time between humans moving to the Americas and the arrival of humans is closer to 20,000 years—just shy of what has been documented for many species.

“This change comes even though we live on this planet for less than 25 percent of our lifetime,” Roy says. So the amount of time it took the first people to arrive on the new land and the time it has taken to evolve from there to now—all of those seem to be roughly correlated.

So which groups of species did humans first evolve in—the hunter-gatherers, or non-agriculturalists? The researchers found that while there were significant differences between the people who developed agriculture and the ones who developed other modes of life, there were significant similarities in the two groups. The hunter-gatherers developed a small hunter-