Homo naledi, the newly discovered species of ancient human, explained

It lived millions of years ago — and may have buried its dead.

Updated by Joseph Stromberg on September 10, 2015, 5:46 p.m. ET

Over the past two years, an international team of scientists has discovered more than 1,500 mysterious fragments of bone in a tiny cave in South Africa. Thursday morning, the team announced that the fossils are from a new species of ancient human that is believed to have lived 2 to 3 million years ago: Homo naledi.

They appear to resemble another ancient hominin species, Homo erectus, but they have much smaller brains, more along the lines of a gorilla's. There's even tantalizing evidence that they might have buried their dead — something scientists previously thought only modern humans did.

When it comes to the study of human evolution, all this is a really big deal. To date, we know of only a handful of other species similar enough to us to fit in to our genus: Homo. Scientists will debate this designation for H. naledi — as they do for all newly discovered species — but the bottom line is that these fossils, detailed in a pair of new papers in the journal eLIFE, give us a fascinating glimpse into a new part of our ancient history.

How are we related to the new species?

That's hard to answer. They could, theoretically, be our direct ancestors. But it's much more likely they were our ancestors' cousins, who diverged, evolved their own unique traits, and at some point died off.

Why don't we know? A good analogy for our current situation is that the many semi-human-like species that predated us made up a complicated, densely branching family tree. But today, every single branch of that tree has disappeared, minus the last twig: us.

Using fossils, we can get a rough idea of what some of the branches looked like, but it's really difficult to put them all together accurately.

As such, we know of a dozen or so species that evolved sometime in the past 10 million years — when our ancestors first split off from the ancestors of chimps — but we don't know exactly how all these species fit together. In some cases, we're not even sure if certain fossils are from different species or the same one. The best we can do, at the moment, is roughly put the species into groups, based on shared traits:

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http://www.vox.com/2015/9/10/9301479/homo-naledi-species-hominin