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Human ancestry 2 – a meander through a couple of million years’ time and a world of space

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Man is descended from a hairy, tailed quadruped, probably arboreal in its habits.

Charles Darwin

Homo neanderthalensis, with a very bad toothache

 

So in this second post I’ll take a little look at Paranthropus and then try to make sense of the move from Australopithecus whateva to Homo whateva, and so on….

There’s a lovely vid about Paranthropus here, which I’ll take much of the following from. There are three known species, P aethiopicus (about 2.7 to 2.3 mya), P boisei (2.3 to 1.4 mya), both only found so far in eastern Africa, and P robustus (2 to 1.2 mya), in southern Africa. They’re all robust species, as opposed to the gracile species A africanus. They have large cheekbones, jaws and teeth, and a prominent sagittal crest across the top of the cranium, a feature shared by gorillas and orang-utangs, and which evolved to attach strong chewing muscles down to the jaw. Apart from these robust characteristics, they shared many features with australopithecines, and have even been defined as robust australopithecines by some. It’s always difficult to split up (or lump together) specimens when only small fragments are found, so there’s a hunt on for more, and bigger, bits and pieces. From what they’ve got, though, it’s estimated that they had a cranial capacity of 475-545 cc, not much more than the average chimp, with a height of about 156cm (just over 5 feet) and a weight of 40-50kg. Smallish perhaps, but I’d be willing to bet they had a pretty impressive muscle to fat ratio. They also appear to have been sexually dimorphic to a greater degree than humans, suggestive of dominant males fighting over females, as in the case of gorillas. There’s also some evidence that the females lacked or had a less prominent sagittal crest. 

How are the Paranthropus species related to modern humans? Surprise surprise, we don’t know, and the pathways to and between the various types of Homo just get more complicated. They may simply have died out, as the more recent Neanderthals did. Researchers desperately await more finds, and more techniques for connecting the dots. 

So, leaving Paranthropus behind, it’s clear from my last post on the subject that tracing the path from our common ancestor with bonobos (my fave ape) has been a fraught process of speculation and disputation, but of course we have no choice but to keep on trying to trace that path. So, what’s the most recently-lived species of Australopithecus, and the most ancient of the Homo species, as far as we know? 

The species A africanus and A sediba seem currently to be in competition to be the immediate ancestor to Homo habilis along the pathway to H sapiens, though there may have been an intermediate, as yet undiscovered, species.

A africanus is known from four sites, all in South Africa, but dating the specimens has been difficult and controversial. The first discovery, the Taung child (1925) is still not clearly dated, and claims for it suffered at the time of its discovery, and for decades afterwards, due to the Piltdown hoax, which I won’t go into here. However, in the mid 1930s the first adult australopithecine was found, and eventually given the A africanus moniker. Evidence of bipedality in this and another adult female, found in 1947, together with evidence of a cranial capacity of about 485 cc for both, was striking evidence that bipedality long preceded brain growth (it has since been mooted as a result of reduced forestation and increased savannah-like environments through climate change, though bipedal traits seem to have existed even before this). A lack of facial projection in these specimens was suggestive of advancement towards modern humanity. And just by the bye, evidence of tool-making among hominins now goes back to 3.4 mya, associated with the A afarensis species. A fourth specimen, ‘Little Foot’, dated to around 3.7 mya, was found in the nineties, but there’s debate about whether it belongs to A africanus or a ‘new’ species, A prometheus (actually suggested by Raymond Dart decades ago). There’s an interesting piece on this here.

I wouldn’t want to be quoted on this, but it seems that the A africanus fossil of a skull now known as ‘Mrs. Ples’ is the most recent A africanus fossil ever found, dated to about 2mya. But what about A sediba? This is the most recently discovered australopithecene, mostly associated with Lee Berger (and his young son), who discovered the first bones in 2008, in South Africa. It has been argued, by its discoverers, to be the most likely transitional species between A africanus and either Homo habilis or H erectus (and it should be noted that many consider H (or A) habilis to be an australopithecine, its placement as Homo being largely based on the use of flaked stone tools, at a time when tool use by australopithecines wasn’t known).

So I think I’ll skip this controversy for now, as I want to get to the more recent radiation of Homo species. Having said that, immediately I start looking at the earliest forms given the Homo moniker, such as H habilis, H erectus and H ergaster, I encounter vast uncertainty and controversy, not to mention my own ignorance. I’ve already discussed H habilis; H ergaster (1.9 to 1.4 mya), according to Wikipedia, ‘is now mostly considered either an early form, or an African variety, of H erectus‘. Oh dear, I thought H erectus was African!

In fact, the first fossils identified with H erectus were found in Eurasian Georgia and in China, but the species may have back-migrated to Africa. Or maybe not. I’m on the verge of giving up here, but I’ll extricate myself from the mess by listing and briefly discussing the various forms of Homo that have been postulated. These aren’t necessarily in chronological order.

  1. H habilis (approx 2.1-1.5mya) – short but with longer arms compared to modern humans, with a cranial capacity of around 700 cc. Used stone tools. Relatively robust, compared to H ergaster. Contested classification. Probably co-existed with H erectus. Only found in Africa.
  2. H ergaster (approx 1.9-1.4mya) – I’ve used the Wikipedia existence range here, but the Australian museum suggests that arguments about existing classification of specimens may extend that range up to 700,000 ya. They also point out that some don’t accept this classification at all, preferring H erectus. They were relatively hairless and more closely resembled modern humans than earlier types. Possible specimens found in modern Kenya, Ethiopia, South Africa, and most notably in Georgia (Eurasia), which suggests first emergence of early humans from Africa occurred about 1.7mya. Cranial capacity, about 860cc .
  3. H erectus (approx 1.8mya- 100,000ya?) – first found in Java, other specimens found in Indonesia, China and Africa. Short and stocky with heavy brow ridges. Sometimes hard to separate from H ergaster, especially the African specimens. H erectus is now more widely believed to be a side-branch, and H ergaster our more direct, if more ancient, ancestor. Cranial capacity about 1050cc.
  4. H rudolfensis (approx 2.4mya- 1.8mya) – specimens found in modern Malawi and Kenya. A contested classification, could be lumped in with H habilis. There is always a difficulty when dealing with limited specimens, which might be atypical, juvenile or of unknown gender. Anyway, estimated cranial capacity, about 750cc. Size and shape insufficiently known.
  5. H heidelbergensis (c700,000-300,000 ya) – evolved in Africa, but in Europe by 500,000 ya (African fossils are mostly older). Lived and worked in co-operative groups, using a variety of tools. Specimens found in England, France and Spain as well as in the region of Heidelberg, Germany. Possibly as far east as northern India. Also in Zambia and South Africa. Physically tall, up to 180 cms, suggesting descent from H ergaster. Brain capacity approx 1250cc.
  6. H neanderthalensis (?800,000-40,000 ya) – some have argued that they were around as recently as 28,000 years ago. The first fossil was found in the 1820s, and was the first fossil of any extinct hominin ever found. Their cranial capacity, at 1500cc, is larger than that of H sapiens, not surprisingly due to their larger overall build (shorter but much more solid). No specimens found as yet in Africa, but a large number of finds throughout Europe and the Middle East (and possibly in China) allow us to build a clearer picture of Neanderthals than any other extinct hominin. They used a variety of tools, which they may have obtained through trade with modern humans. They wore animal hides and used fire for warmth, cooking and protection. Physically they were thickset, with heavy brow ridges and a relatively receding forehead, a forward-projecting face, a large, broad nose, and strong neck muscles. It’s now known, of course, that they interbred to some degree with modern humans, but it’s also likely that they competed with them for scarce resources, especially during ice ages. Though we don’t now consider them to be ‘nasty, brutish and short’ it may well be that the greater resourcefulness of H sapiens hastened their demise.
  7. H rhodesiensis (c800,000-120,000 ya) – now generally seen as an African subspecies of H heidelbergensis, with specimens found in Rhodesia/Zambia, Ethiopia and Tanzania.
  8. H cepranensis (c900,000-800,000 ya) – based on one fossil skull cap, or calvaria, unearthed near Ceprano, Italy in 1994. Others are for H heidelbergensis. The dating is also highly contested, with some arguing for around 450,000 ya. There’s probably quite a few more of this sort – but every new find is exciting.
  9. H denisova (? – 15,000 ya) – This isn’t an agreed taxonomic title, but the Denisovan finds are certainly exciting, with mitochondrial DNA being recovered from the first find (in a Siberian cave), the finger-bone of a juvenile female (how do they know that??). Other specimens have been found in the same cave, and another has been found in Tibet. There’s not enough material for us to picture this species, but the DNA tells us that they interbred with Neanderthals, and to a lesser degree with Melanesians, Papuans and Aboriginal Australians.
  10. H floresiensis (c190,000-50,000 ya) – found only on the Indonesian island of Flores. Another exciting, and puzzling, recent find. Could they have been killed off by those passing though on their way to Australia? Researchers are still hoping to recover mitochondrial DNA from the most recent specimens. Physically, these were unique humans with a very small stature and a cranial capacity of 380cc (chimp size), though with an enlarged Broadman area 10, which is associated with complex cognitive abilities. Other skull features, though, suggest a primitiveness going back more to H erectus. Tools found at the site have raised controversy. Do they belong to H floresiensis? They don’t easily equate with such a small brain. There is no precedent. Much still to be learned.

So I’ve raised far more questions for myself than I’ve answered. Hope to come back to this topic in future, with a focus on bipedality, climate effects, the beginnings of ‘culture’, and migration, among other things.

References

https://australianmuseum.net.au/learn/science/human-evolution/ (a great site, with links to details on particular species)

Paranthropus evolution (video), by Stefan Milo, 2019

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

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

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

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

http://humanorigins.si.edu/evidence/human-fossils/species/homo-habilis

Written by stewart henderson

October 30, 2019 at 9:59 pm

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