Wednesday, 21 October 2015

How Science Works - New Thinking From Old Teeth

These 47 human teeth, dated to 80,000-120,000 years ago, were found in a limestone cave system in Daoxian, China.
Photos: S. Xing and X-J. Wu
Source: Nature (reprinted under licence #3733841429431)
Teeth from China reveal early human trek out of Africa | Nature.

An example of how science continually reassesses what it thinks it knows and adjusts its theories in the light of new evidence, was published a few days ago in Nature. It's things like this that makes science such an exciting, living thing, full of surprises and so rewarding for anyone interested in gaining a real understanding of the world we live in.

We thought we had the pattern of the expansion of fully modern humans out of Africa and into Eurasia pretty much worked out, give or take a few thousand years. It also seemed fairly clear that our interaction with the Neanderthals who had been indigenous to Europe for about 200,000 years before we arrived was one of inexorable replacement and extermination of Neanderthals by moderns over a period of 10-20,000 years, maybe less, due to superior technology, maybe higher intelligence, or more organised social structure. Even domestication of dogs by moderns has been suggested.

Now, a team of paleoanthropologists have come up with what some are claiming to be conclusive evidence that modern humans lived in China between 80,000 and 120,000 years ago. If this is true, it renders the whole timescale redundant and raises the question of how Neanderthals held us at bay in Europe for so long.

Before creationists get too over-excited by this, none of it is inconsistent with the basic picture of modern human evolution in Africa and subsequent spread into Eurasia, or the picture of Neanderthals evolving in relative isolation in Europe from an earlier expansion out of Africa of an archaic hominid such as Homo erectus. What we are talking about is the timescale.

The team led by Wu Liu of the Chinese Academy of Sciences, Beijing found the 47 teeth in Fuyan cave in Daoxian, in southern China in deposits which had been coated by stalagmites which have been dated to at least 80,000 years old. Since the teeth obviously predate the stalagmites by some considerable time, during which their previous owners seem to have dissolved, so they could be as much as 125,000 years old. And yet they are morphologically almost identical to those of modern Europeans with the thin roots, flat crowns and small size.

The hominin record from southern Asia for the early Late Pleistocene epoch is scarce. Well-dated and well-preserved fossils older than ~45,000 years that can be unequivocally attributed to Homo sapiens are lacking. Here we present evidence from the newly excavated Fuyan Cave in Daoxian (southern China). This site has provided 47 human teeth dated to more than 80,000 years old, and with an inferred maximum age of 120,000 years. The morphological and metric assessment of this sample supports its unequivocal assignment to H. sapiens. The Daoxian sample is more derived than any other anatomically modern humans, resembling middle-to-late Late Pleistocene specimens and even contemporary humans. Our study shows that fully modern morphologies were present in southern China 30,000–70,000 years earlier than in the Levant and Europe. Our data fill a chronological and geographical gap that is relevant for understanding when H. sapiens first appeared in southern Asia. The Daoxian teeth also support the hypothesis that during the same period, southern China was inhabited by more derived populations than central and northern China. This evidence is important for the study of dispersal routes of modern humans. Finally, our results are relevant to exploring the reasons for the relatively late entry of H. sapiens into Europe. Some studies have investigated how the competition with H. sapiens may have caused Neanderthals’ extinction (see ref. 8 and references therein). Notably, although fully modern humans were already present in southern China at least as early as ~80,000 years ago, there is no evidence that they entered Europe before ~45,000 years ago. This could indicate that H. neanderthalensis was indeed an additional ecological barrier for modern humans, who could only enter Europe when the demise of Neanderthals had already started.*

The earliest unequivocally modern humans in southern China
Wu Liu, María Martinón-Torres, et al. Nature (2015) doi:10.1038/nature15696

*© 2015, Rights Managed by Nature Publishing Group. Reprinted with permission under licence #3733840207799

Of course, it's always possible that they could be a case of convergent evolution in a population of H. erectus so my feeling is that this find needs further corroborating evidence. Never-the-less, if it is confirmed it means that H. sapiens probably left Africa and spread by a southern route into Asia before coming into contact with Neanderthals in the western part of their range. At that time, Europe especially was an inhospitable Ice Age environment to which Neanderthals had adapted over the previous 200,000 years, so they may well have been capable of holding moderns at bay. There is actually no evidence for a lower intelligence and their technology was not too dissimilar from moderns.

Another hypothesis which is very probably wrong but which is actually supported by this find is that modern humans evolved in China, not Africa, out of an archaic hominid such as H. erectus of which H. e. pekinensis was an example; a hypothesis favoured by some Chinese anthropologists but by almost no-one else.

But there we are. We now have reasons to doubt the precise details of what we thought we knew but that little bit of uncertainty is the spur to more research and whatever the outcome, our knowledge will be a little close to the real truth which is out there waiting to be discovered.

Don't you just love science?

Wouldn't it be horrible to be like a creationist and have to pretend to know things you don't know and to be unable to change your mind when the evidence changes, in case a magic invisible man hurts you.

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