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Hank tells us about new and confusing discoveries in the field of Human Evolution.

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Sources:
http://www.eurekalert.org/pub_releases/2013-10/iu-snk101713.php
http://www.sciencemag.org/content/342/6156/297.full
Have we discovered our most important human ancestor? Did Neanderthals first appear hundreds of thousands of years earlier than we thought? Could the human family actually be less diverse than we imagined?

In the past few days scientists have raised these questions and provided some unexpected possible answers. While we don't have anything close to a complete picture of humanity's origins, this recent research has given us some tantalizing clues about where we came from. I'm Hank Green, and this is SciShow News.

(Intro)

Humans are strange animals and two new studies are reminding us just how out of touch we are with why humans are so uniquely awesome.

The first, published in the Proceedings of the National academy of Sciences this Monday, outlined the giant international mind boggle that took place when a group of anthropologists tried to apply new methods to a classic question: Who is our common ancestor with the Neanderthals?

Hoping to pioneer a more testable quantitative method of answering this question in a field that is fairly qualitative, a group of Australian, Spanish, and American researchers turned to our teeth. Specifically, they graphed twelve hundred different points on the molars taken from thirteen different species of human ancestors. Then they used some fancy statistical analysis to identify which tooth shapes could have evolved into both our teeth and the teeth of Neanderthals. Whoever had the molars that fit description, the reasoning went, could be the ancestor of both human species.

But they concluded, with high statistical confidence, that none of them could have. Which suggests that we still haven't discovered the common ancestor that we share with our thick-browed cousins.

But on top of this, the scientists also found that many of the different species that lived in Europe over time, like Homo heidelbergensis and Homo antecessor, had molars that looked a lot like Neanderthal teeth, even tough some of those were nearly a million years old. The weird thing is, we thought that Neanderthals weren't even a thing until about three hundred and fifty thousand years ago.

So this is all very interesting, and a little confusing, and I'm sure a little corner of the internet will no doubt start drawing all kinds of nutty conclusions about what this might mean for human evolution, but the scientists say that the new study, quote "tells us that there are still new Hominid finds waiting to be made." In other words: the answers are out there, just waiting to be discovered.

The human puzzle got even more interesting with the cover story from the October 18th issue of Science, which detailed the controversial study of Homo erectus, one of our most recent ancestors. Excavating a site in the republic of Georgia, a team of anthropologists uncovered five skulls of the Homo genus, and they were really, really weird. All five skulls had drastically different traits, even though they were all found in the same spot, and about the same age - about 1.8 million years old. Some of the variations could be explained by differences in age and sex, but the most unusual specimen, an adult male, had the protruding upper jaw and tiny brain case of much earlier human ancestors like Australopithecus, but the general skull and body shape of Homo erectus.

As a group, the specimens seemed to have mostly Homo erectus-like traits, and a 3D analysis confirmed that the variation between them was within reason for members of a singles species - just a highly variable species. So the team ended up classifying the specimens as belonging to a single, early form of Homo erectus, which they called Homo erectus ergaster georgicus. However, they say the skulls were different enough that, if they hadn't come from the same spot, they would likely have been classified as different species. So putting them all in the same category has set up a debate about how we think about our Hominid ancestors, and about ourselves. If these diverse specimens are all members of the same species, how does the confusing patchwork of even older Hominid remains in Africa compare? And what about us? What if the family Homo is less diverse than we thought? In that case, what does it mean to be human at all, a million years ago or today?

Just like with the study of our Neanderthal brethren, the skulls found in Georgia don't give us any easy answers, but they do broaden our knowledge enough to make us revise what we think we know. Which is how science is supposed to work.

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