View Full Version : Older split between "modern" humans and neanderthal?

Prisoner Of Ice
11-04-2013, 01:08 AM

In the last five years, anthropologists have used DNA to reconstruct the evolutionary history of humans. Researchers have suggested a range of dates for when the last common ancestor of our lineage and Neanderthals could have lived. (Related: "Last of the Neanderthals.")

The dates range from more than 800,000 years ago to less than 300,000, with many estimates in the neighborhood of 400,000 years ago. According to some studies, this time frame would seem to match that of the extinct species Homo heidelbergensis, which has been found in Africa, Europe, and possibly Asia.

But this may not be so. A new study theorizes that the last common ancestor of H. sapiens and Neanderthals lived longer ago than previously expected, with fossil evidence yet to be uncovered.

Using a collection of 1,200 premolars and molars from a variety of prehistoric humans, the researchers pinpointed specific landmarks on the teeth. The landmarks were then used to reconstruct the tooth shapes of our common ancestors at critical points in evolutionary history.

The logic behind this method, Gómez-Robles says, is that "the most likely dental shape of an ancestral species is an intermediate shape between the one observed in both daughter species." In the case of H. sapiens and Neanderthals, the last common ancestor of both lineages would be expected to have teeth with a shape and anatomy in between those of the two species.

With that hypothetical shape in mind, Gómez-Robles and coauthors compared what was expected against fossils found so far.

"If a fossil species is very similar to the expected ancestral morphology, then that species is a plausible ancestor," Gómez-Robles says, though she stresses that such a match is a possibility rather than definite proof of ancestry.

This is interesting to me because these little tooth differences, called perikymata, vary along the same proportions in modern humans and ancient humans. Meaning that this is largely retained by europeans, is much lighter in easterners, and barely exists in pure africans.

Estimates based on DNA show that the last common ancestor of H. sapiens and Neanderthals lived around 400,000 years ago. This made H. heidelbergensis, a widespread species alive at the time, seem like a good candidate for that ancestor.

Thing is estimates of this nature are notoriously inaccurate so you can't take them seriously.

The new study contradicts this idea. The tooth reconstruction of the last common ancestor of humans and Neanderthals created by Gómez-Robles and colleagues doesn't match the teeth of H. heidelbergensis.

In fact, the researchers found that none of the human species living during the time predicted by genetic data fit the tooth pattern generated by the new study. More than that, "European species that might be candidates show morphological affinities with Neanderthals," Gómez-Robles says, which hints that these humans were already on the Neanderthal side of the split.

This suggests that the last common ancestor of H. sapiens and Neanderthals lived sometime earlier, perhaps as far back as one million years ago.

Hmm, surprising result but one that is hard to deny if they did everything right. Archaeologically, we see that these tooth patterns are good at tracking neanderthal genetics.

Paleoanthropologists have yet to find our last common ancestor with Neanderthals. Tracking this elusive human will require going back to museum collections and continuing searches in the field.

From the new study's results, Gómez-Robles says that "we think that candidates have to be looked for in Africa." At present, million-year-old fossils attributed to the prehistoric humans H. rhodesiensis and H. erectus look promising.

This critical window of human prehistory in Africa is still cloudy. "There are not so many African fossil remains dated to one million years ago," Gómez-Robles says, and those that have been found are often attributed to H. erectus.

But do they really belong to this species? There may be an as-yet-unknown human hiding in the mix, and this human may be key to solving the puzzle of when our ancestors split from Neanderthals.

Whether that species is waiting to be discovered in the field or is hiding within the broken and scattered remains of fossils already collected is a mystery waiting to be solved.

Oh boy, they really try hard to make everything afrocentric these days.

However, H. rhodesiensis indeed has many neanderthal characteristics but a much different skull shape. In fact they have been called the Third Hominid by some "wackos" who have some interesting ideas about evolution. Hopefully this can be tested out because we have DNA in some pygmies that almost certainly comes from H. rhodesiensis intermixing.

Goes to show though, how little info we really have. Things have changed a lot lately due to findings in central and east asia and better dating for old artifacts, but there's many more gaps than there are filled in material.