Science & Technology

A New Species of Ancient Human May Have Just Been Discovered

Once upon a time, scientists knew the story of human evolution. It was linear and began in Africa. The first human ancestors, or hominins, spent millions of years on the continent, evolving big brains, flat foreheads, and other modern traits before traipsing off to colonize the rest of the world. Recent fossils, though, have complicated that narrative — and a new one has muddled it even more.

An Unexpected Fossil "Bonanza"

The complications began in 2007 in a cave: Callao Cave on Luzon, the largest island in the Philippines. At the time, it wasn't thought of as an important archaeological site, especially for people studying human evolution. Never connected to the mainland with a land bridge, it was thought of as an isolated place that early hominins — confined, as they were, to Africa—couldn't have accessed.

But then, an archaeology graduate student named Armand Mijares found a weird bone. It was mixed in with deer and pig bones, but this bone looked human. It turned out to be a metatarsal, or foot bone, distinctive enough that it had to come from the human genus — so, from a hominin. Carbon dating found the metatarsal was roughly 67,000 years old. Apparently, early humans had crossed the water to Luzon.

Mijares published a paper on that bone in 2010, but he kept digging in Luzon, too. On ensuing digs, he and his colleagues found a "bonanza" of other hominin bones: five teeth, two finger bones, two toe bones, and a femur, all from roughly the same era as the first bone. They came from three individuals, all told; prehistoric people apparently loved to die in Callou Cave.

These weren't your typical hominins, though. In a paper published this month in Nature, Mijares and his co-authors argued that these bones come from an entirely new species of hominin: Homo luzonensis.

A New Species?

The Callou Cave fossils were definitely unusual. For one, the molars were very small for hominin teeth: roughly eight by 10 millimeters. Since tooth size correlates with height, scientists suspect the teeth belonged to a person roughly 3 feet (1 meter) tall. Meanwhile, the curved finger and toe bones suggest a life spent climbing or swinging through trees.

But not all scientists agreed that the new bones mean a new species.

By the most popular definition, a species is a group of organisms that can mate and produce fertile offspring. The definition isn't perfect, though; in some cases, animals in different species do have fertile offspring, improbably. All told, there are at least 32 possible definitions of a "species." Ultimately, a "species" is a category humans constructed, and however you define it, it doesn't map perfectly onto the realities of the natural world.

Not only is term "species" internally conflicted, the Callou Cave bones aren't perfect evidence for a new species themselves. For one, by the time Mijares and his colleagues discovered them, the bones were totally stripped of DNA; not only were they were old, but they had also baked in the tropical sun for literal millennia. They didn't add up to a complete skeleton, either; only a fraction of one.

That means it's hard to prove that Homo luzonensis fundamentally differs from, say, Homo floresiensus (another, also-dwarflike hominin species, discovered in 2004). To some scientists, proclaiming a new species feels hasty. Others are all in.

"This is a truly sensational finding," archaeologist Adam Brumm, who wasn't involved in Mijares' research, told National Geographic.

Species breakthrough or no, though, one thing seems clear: Our ancestors were more spread out, across space and species, than previously thought. Instead of a linear progression, human evolution was likely a swirl of chaos, with multiple competing hominin species coexisting in a single era.

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Learn more about early humans in "Almost Human: The Astonishing Tale of Homo naledi and the Discovery That Changed Our Human Story" by Lee Berger and John Hawks. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Mae Rice April 23, 2019

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