We Homo sapiens didn’t used to be alone. Long ago, there was a lot more human diversity; Homo sapiens lived alongside an estimated eight now-extinct species of human about 300,000 years ago. As recently as 15,000 years ago, we were sharing caves with another human species known as the Denisovans. And fossilized remains indicate an even higher number of early human species once populated Earth before our species came along.
“We have one human species right now, and historically, that’s really weird,” said Nick Longrich, an evolutionary biologist at the University of Bath in the United Kingdom. “Not that far back, we weren’t that special, but now we’re the only ones left.”
So, how many early human species were there?
When it comes to figuring out exactly how many distinct species of humans existed, it gets complicated pretty quickly, especially because researchers keep unearthing new fossils that end up being totally separate and previously unknown species.
“The number is mounting, and it’ll vary depending on whom you talk to,” said John Stewart, an evolutionary paleoecologist at Bournemouth University in the United Kingdom. Some researchers argue that the species known as Homo erectus is in fact made up of several different species, including Homo georgicus and Homo ergaster.
“It’s all about the definition of a species and the degree to which you accept variation within a species,” Stewart told Live Science. “It can become a slightly irritating and pedantic discussion, because everyone wants an answer. But the truth is that it really does depend.”
The Smithsonian National Museum of Natural History has listed at least 21 human species that are recognized by most scientists.