Our extended human family is full of interesting characters, and scientists have just introduced the world to the newest oddball of the human clan.

Its name is Homo naledi. Scientists discovered it deep within a cave in South Africa in the fall of 2014, and it's taken them nearly a year to extract and sort through the 1,500 or so fossil fragments described in the journal eLife. The bones belonged to at least 15 different individuals.

The sheer magnitude of the find is reason enough for the excitement, but its hodgepodge of primitive and advanced features is what still has scientists pondering away nearly a year later. One of those advanced features appears to be the behavior that created this archaeological gold mine in the first place: burying their dead. It's still a hypothesis at this point, but it's the best explanation science has so far for the collection of so many skeletons in that dark and inaccessible spot.

What convinced scientists that this species is indeed a member of the human genus Homo is its extraordinarily human-like feet and long legs — features that suggest Homo naledi was a long-distance walker. The lead researcher behind the discovery, Lee Berger of the University of Witwatersrand in South Africa, described this trait as "the defining characteristic of the genus Homo" in an interview with The Atlantic.

As the case of Lucy the hominin skeleton famously demonstrated in 1974, some human-like ancient species weren't quite human enough to make it into the Homo genus. The most ancient and ape-like hominids discovered thus far are part of the genus Ardipithecus, and there has been much debate in the scientific community over whether they walked upright at all. Lucy ultimately got filed under the genus Australopithecus largely because she had adaptations for living in trees as well as on the ground.

Lucy and her fellow Australopithecans lived about 3 to 4 million years ago, just before Homo hit the scene. In the midst of that transition, a third not-quite-human genus cropped up. Members of the Paranthropus group are defined by their large teeth and jaws, which allowed them to snack on a wide variety of foods.

So far, it looks like Homo naledi is a good candidate for the title of earliest Homo species based on its features, but no one knows for sure just yet. Many scientists are flabbergasted and frustrated that Berger and his colleagues have not yet solved this mystery by using chemistry to determine the fossils' age.

The most striking mismatch of Homo naledi is that it had a remarkably tiny brain, despite its relatively lanky, human-like skeletal structure. In fact, most of its upper body is quite primitive compared to its lower parts — with shoulders poised for hanging from trees and curved fingers suited for curling around branches.

This mosaic of modern and primitive features suggests that Homo naledi was right on the cusp of the transition between Australopithecans like Lucy and Homo species like us. It has already proven, however, that we still have a lot to learn from digging through our evolutionary family's skeletal scrapbook.

Photo: Tim Evanson | Flickr

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