an autodidact meets a dilettante…

‘Rise above yourself and grasp the world’ Archimedes – attribution

Archive for the ‘Denisovans’ Category

modern humans are getting less modern, in unexpected places

with one comment

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