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Posts Tagged ‘Neanderthals

modern humans are getting less modern, in unexpected places

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Taken from the website of Science magazine

In recent years we’ve been almost overwhelmed by paleontological discoveries (and re-analyses of earlier discoveries), from giant worm jaws to a new subclass of cephalopod to a new semi-aquatic non-avian dinosaur to the oldest fossils yet found of that strange species, Homo sapiens. 

I’ve decided to focus on the last example, for now. Homo sapiens fossils discovered at Jebel Irhoud in Morocco in the sixties, and long thought to have been some 40,000 years old, came under increasing ‘suspicion’ from palaeontologists, beginning in the eighties, due to various curious anomalies. More intensive searching at the Jebel Irhoud site recently has led to a wealth of discoveries, ‘including skull bones from five [human-like, though with a different brain-case, especially at the back] individuals who all died around the same time’. And thanks to the new thermoluminescence dating technique, which is applied to heated or burned substances (it’s a measure of accumulated radiation), a date of 300,000 years was calculated for the tools found near the fossils, and by association for the fossils themselves. This makes them over 100,000 years older than those found in Ethiopia. The Ethiopian fossil discoveries gave rise to the idea that ‘modern’ humans began life in a small region of East-Central Africa and gradually spread, but the revelation about the Moroccan fossils means a revision, or overturning, of that hypothesis.

You’ll notice I’ve put modern in skeptical quotes. It seems to me nobody will agree on what a modern human really is, or whether it’s decided entirely on anatomical or physiological features. If you found yourself suddenly transported to the days of Sargon and the Akkadian civilisation, only 4,500 years ago, you probably wouldn’t have the impression you were living among modern humans – depending on how prepared you were for the culture shock. Of course, paleontologists would have different measures for modernity – brain size, skeletal features and such – but these are necessarily imprecise given individual variation and the sparsity of really good fossils. And there’s also the matter of incremental, barely discernible change. For example, our 300,000-year-old Jebel Irhoud specimens are, perhaps, the oldest known modern human specimens, but it would be silly to argue that their parents weren’t just as modern – and what of their grandparents? And in this way we can go back another 10,000 years, or maybe 50,000, without seeing much difference. This has always been the most difficult thing to get my head around, not only for H sapiens but for any species. When does Australopithecus afarensis start/stop being Australopithecus afarensis? When did a chimp distinguish herself from a bonobo, and when did they both get differentiated from their predecessor? Are we taking hard and fast taxonomy too seriously? Maybe I’ll return to that some time…

Meanwhile, another recently revealed discovery has added to the ‘out of Africa’ confusion, which many thought was becoming less confused, with something like a consensus that H sapiens  emerged from Africa between 70 and 100 thousand years ago and dispersed globally, with the oldest Australian human possibly dating back as far as 65,000 years.

The discovery of a human jawbone and teeth in Israel that date back nearly 200,000 years has messed up that simplifying story, and it’s only one of a number of finds that are making the experts get confused – and excited – again. The jawbone find, combined with sophisticated tools and weaponry, is solid evidence of H sapiens coming out of Africa much earlier, and perhaps on an irregular basis depending on climatic conditions and resources. Human teeth found in China, and human fossils in Sumatra, dating to at least 70,000 years ago, tend to confirm this hypothesis. Other fossil discoveries in Israel are complicating the picture. The Eastern Mediterranean seems to have been a crossroads where various early human species may have interacted.

These new discoveries appear to confound the genetic evidence that we’re all related to an out-of-Africa population that emerged well under 100,000 years ago, but it seems these early populations died out or returned to Africa.

Yet there are so many mysteries still to solve. What about the strange Denisovans? We have so little fossil evidence, yet enough to map almost the entire nuclear and mitochondrial genome – a testament to modern technology. Analysis of their mtDNA suggests that they migrated out of Africa much earlier than the modern humans above-mentioned, but later than H erectus. They apparently branched off from the human line 600,000 years ago, and from Neanderthals about 400,000 years ago. The fullness and fascinating richness of the Wikipedia article on the Denisovans, garnered from such minute fossil evidence, is a source of great wonder to me. The specimens (of four distinct Denisovans) were well preserved due to the icy temperatures in the Siberian cave, near the Mongolian-Chinese border, where they were found. The finger bone, dated to about 40,000 years BP (Before Present, a new designation to me, and a welcome one), has yielded both mitochondrial and nuclear DNA, which has shown the Denisovans to be distinct from both Neanderthals and modern humans, and that they share a common ancestor with Neanderthals. Other excavations of the cave show that it was inhabited at least 125,000 years ago. mtDNA analysis has apparently revealed that the three, H sapiens, Denisovans and Neanderthals, shared a common ancestor about 1 million years ago. I’m writing these facts, if they are facts, as I find them, while wondering what they mean, and especially how the evolutionary tree can be visualised, but it’s pretty difficult, especially when you consider interbreeding. Looks like I’ll have to write and do the research for half a dozen posts before I start to get it straight in my own head. Anyway, here’s one interesting chart I’ve found.

 

There are clearly more mystery hominids to be found, to fill out the complicating picture. And of course I’ve mentioned the genetics and genomics only in passing, but again it’s astonishing what they can find these days by comparing these genes with what we know of some modern human populations. For example, studies of the Denisovans genome found ‘a region around the EPAS1 gene that assists with adaptation to low oxygen levels at high altitude’, already known from analysis of modern Tibetan genes.

Hoping to keep myself up to date with all this, if I don’t get too distracted by the zillions of other fields of enquiry worth keeping up with…

References

https://www.theguardian.com/science/2018/jan/25/oldest-known-human-fossil-outside-africa-discovered-in-israel

https://www.theatlantic.com/science/archive/2017/06/the-oldest-known-human-fossils-have-been-found-in-an-unusual-place/529452/

https://en.wikipedia.org/wiki/Denisovan

 

All the excitation about Trump having tried to sack Mueller annoys me because it makes me – well, too excited. I have to learn to be patient. The Mueller enquiry will end when it does, and it’s sure to end dramatically. Still, I hunger for another indictment, or equivalent headline. One point worth worrying about though, is what happens when Trump goes? The whole administration should go, but that’s not what happens in the US. No snap elections, no double dissolution. Another weakness of the Presidential system, it seems to me. In the US, you vote for a personality, and that personality gets to build a team around him (it’s always been a bloke), whereas in most advanced western nations, the country’s leader has risen through the ranks of the team, much like the captain of a soccer team, who’s given the captain’s armband, not because she’s the best player – though she quite often is – but because she’s the most inspiring leader. If that captain falls afoul of the law, another competent team member can take on the job. In the case of the US Presidency, the team is tainted by the captain’s failings because he’s personally chosen the lot of them – in this case largely because of their political ignorance, which he regards as a positive.

 

Written by stewart henderson

January 29, 2018 at 10:31 pm

When was the first language? When was the first human?

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Reading a new book of mine, Steven Pinker’s The sense of style, 2014, I was bemused by his casual remark on the first page of the first chapter, ‘The spoken word is older than our species…’. Hmmm. As Bill Bryson put it in A short history of nearly everything, ‘How do they know that?’. And maybe I should dispense with ‘they’ here – how does Pinker know that? My previous shallow research has told me that nobody knows when the first full-fledged language was spoken. Furthermore, we’re not sure about the first full-fledged human either. Was it mitochondrial Eve? But what about her mum? And her mum’s great-grandad? Which raises an old conundrum, one that very much exercised Darwin, and which creationists today love to make much of, the conundrum of speciation.

Recently, palaeontologists discovered human-like remains that might be 300,000 years old in a Moroccan cave. Or, that’s the story as I first heard it. Turns out they were discovered decades ago and dated at about 40,000 years, though some of their features didn’t match with that age. They’ve been reanalysed using thermoluminescense dating, a complicated technique involving measuring light emitted from escaping electrons (don’t ask). No doubt the dating findings will be disputed, as well as findings about just how human these early humans – about 100,000 years earlier than the usual Ethiopian suspects – really are. It’s another version of the lumpers/splitters debate, I suspect. It’s generally recognised that the Moroccan specimens have smaller brains than those from Ethiopia, but it’s not necessarily the case that they’re direct ancestors, proof that there was a rapid brain expansion in the intervening period.

Still there’s no doubt that the Moroccan finding, if it holds up, is significant, as at the very least it pushes back findings on the middle Stone Age, when the making of stone blades began, according to Ian Tattersall, the curator emeritus of human origins at the American Museum of Natural History. But as to tracing our ancestry back to ‘the first humans’, we just can’t do this at present, we can’t join the dots because we have far too few dots to join. It’s a question whether we’ll ever have enough. Evolution isn’t just gradual, it’s divergent, bushy. Where does Homo naledi, dated to around 250,000 years ago, fit into the picture? What about the Denisovans?

Meanwhile, new research and technologies continue to complicate the picture of humans and their ancestors. It’s been generally accepted that the last common ancestor of chimps and humans lived between 5 and 7 million years ago in Africa, but a multinational team of researchers has cast doubt on the assumption of African origin. The research focused on dental structures in two specimens of the fossil hominid Graecopithecus freybergi, found in Greece and Bulgaria. They found that the roots of their premolars were partially fused, making them similar to those of the human lineage, from Ardepithecus and Australopithecus to modern humans. These fossils date to around 7.2 million years ago. It’s conjectured that the possible placing of the divergence further north than has previously been hypothesised has much to do with environmental factors of the time. So, okay, African conditions were more northerly in those days…

So these new findings and new dating techniques are adding to the picture without clarifying it much, as yet. They’re like tiny pieces in a massive jigsaw puzzle, gradually accumulating, sometimes shifted to places of better fit, and so tantalisingly offering new perspectives on what the whole history might look like. I can imagine that in this field, as in so many others, researchers are chafing against their own mortality, as they yearn for a clearer, more comprehensive future view.

Meanwhile, speculations continue. Colin Barras offers his own in a recent New Scientist article, in which he considers the spread of H sapiens in relation to H naledi and H floresiensis. The 1800 or so H naledi fossil bones, discovered in a South African cave four years ago by a team of researchers led by Lee Berger, took a while to be reliably dated to around 250,000 years (give or take some 50,000), just a bit earlier than the most reliably dated H sapiens (though that may change). Getting at a precise age for fossils is often difficult and depends on many variables, in particular the surrounding rock or sediment, and many researchers were opting for a much earlier period on the evidence of the specimens themselves – their small brain size, their curved fingers and other formations. But if the most recent dating figure is correct (and there’s still some doubt) then, according to Barras, it just might be that H sapiens co-existed, in time and place, with these more primitive hominids, and outcompeted them. And more recent dating of H floresiensis, those isolated (so far as we currently know) hominids from the Indonesian island of Flores, has ruled out that they lived less than 50,000 years ago, so their extinction, again, may have coincided with the spread of all-conquering H sapiens. Their remote island location may explain their survival into relatively recent times, but their ancestry is very much in dispute. A recent, apparently comprehensive analysis may have solved the mystery however. It suggests H floresiensis descended from an undiscovered ancestor that left Africa over 2 million years ago. Those who stayed put evolved into H habilis, the first tool makers. Those who left may have reached the Flores region more than 700,000 years ago. The analysis is based on detailed comparisons with many other hominid species and earlier ancestors.

I doubt there will ever be agreement on the first humans, or a very precise date. We’re not so easily defined. But what about the first language? Is it confined to our species?

Much of the speculation on this question focuses on our Neanderthal cousins as the most likely candidates. Researchers have examined the Neanderthal throat structure as far as possible (soft tissue doesn’t fossilise, which is a problem), and have found one intriguing piece of evidence that makes Neanderthal speech plausible. The semi-circular hyoid bone is located high in the human throat, and is found in the same place in the Neanderthal throat. Given that this bone is differently placed in the throat of our common ancestors, this appears to be an example of convergent evolution. We don’t know the precise role of the hyoid in speech, but it certainly affects the space of the throat, and its flexible relationship to other bones and signs of its ‘intense and constant activity’ are suggestive of a role in language. Examination of the hyoids of other hominids suggests that a rudimentary form of language may go back at least 500,000 years, but this is far from confirmed. It’s probable that language underwent a more rapid development between 75,000 and 50,000 years ago. It’s also worth noting that a full-fledged language doesn’t depend on speech, as signing proves. It may be that a more or less sophisticated gestural system preceded spoken language.

a selection of primate hyoid bones

Of course there’s an awful lot more to say on the origin of language, even if much of it’s highly speculative. I plan to watch all the best videos and online lectures on the subject, and I’ll post about it again soon.

References

https://www.sciencedaily.com/releases/2017/05/170523083548.htm

https://www.vox.com/science-and-health/2017/6/7/15745714/nature-homo-sapien-remains-jebel-irhoud

Did Neanderthals Speak?

http://www.isciencetimes.com/articles/6557/20131220/neanderthals-speak-like-humans-hyoid-bone-study.htm

https://www.newscientist.com/article/2128483-mystery-human-hobbit-ancestor-may-have-been-first-out-of-africa/

https://www.newscientist.com/article/2128834-homo-naledi-is-only-250000-years-old-heres-why-that-matters/

Written by stewart henderson

July 9, 2017 at 11:14 am