Archive for the ‘paleontology’ Category
Human origins far from being resolved – it just gets more fascinating (part 1)
yeah – a few ‘awkward’ species missing from this group
Canto: So we’d all like to solve the riddle – or many riddles, of human ancestry, but the problems are manifold, it seems.
Jacinta: Yes, we’re not just talking about Homo sapiens, or H sapiens sapiens as some would put it, but the whole Homo genus, including neanderthalenis, denisova, floresiensis, naledi, heidelbergensis, rudolfensis, erectus and habilis, and I’m not sure if I’ve got them all.
Canto: Yes and there are lumpers and splitters, but I’m talking even further back, to Paranthropus and the Australopithecines. I watched a DW doco recently that piqued my interest, making me wonder at what date, round-about, did the Homo genus emerge, and what genus did it emerge from?
Jacinta: Well this is a problem for all species and genera really. Think of our favourite apes, the bonobos. In the book Who we are and how we got here, which is all about the new science of genomics and how it’s transforming our understanding of human populations , David Reich wrote of –
a new method to estimate the suddenness of separation of the ancestors of two present-day species from genetic data… When they applied the method to study the separation time of common chimpanzees and their cousins, bonobos, they found evidence that the separation was very sudden, consistent with the hypothesis that the species were separated by a huge river (the Congo) that formed rather suddenly one to two million years ago
D Reich, Who we are and how we got here, p46
Which is all very fascinating, but one to two million years is rather a long time frame.
Canto: Yes, in the DW doco the time frames were also rather flexible – which I suppose needs must. Australopithecines were described as emerging perhaps 3 million years ago and disappearing 2 million years ago, with the Paranthropus genus preceding them by about a million years – or was it the other way around?
Jacinta: And other types are mentioned – often from the most meagre remains. Sahelanthropus, Orrorin, Ardipithecus, and Danuvius guggenmosi, beloved of Madelaine Böhme among others.
Canto: Well D guggenmosi was an interesting but isolated find, dating to around 11.6 million years ago, and of course the remains are fragmentary so there are arguments about its bipedalism and other features. It was a tiny ape, quite a bit smaller than bonobos, the smallest of the extant great apes. Böhme is arguing, I believe, that these discoveries (three specimens were discovered) could push the chimp-human last common ancestor (CHLCA) back a few million years. The CHLCA date is usually given as between 6 and 7 million years ago, but Wikipedia is, currently at least, being more open to a wider range:
The chimpanzee–human last common ancestor (CHLCA) is the last common ancestor shared by the extant Homo (human) and Pan (chimpanzee and bonobo) genera of Hominini. Due to complex hybrid speciation, it is not currently possible to give a precise estimate on the age of this ancestral population. While “original divergence” between populations may have occurred as early as 13 million years ago (Miocene), hybridization may have been ongoing until as recently as 4 million years ago (Pliocene).
Chimpanzee–human last common ancestor, Wikipedia Jan 21 2023
Jacinta: Interesting, and it suggests a lot of work still to be done, and that’s just in relation to the Homo genus. I’d certainly be interested in pursuing the evidence and the debate in future posts, but for now I’m wondering about the immediate ancestors of our species.
Canto: Well, the book Who we are and how we got here tries to sort all that out through the study of population genetics and genomics, though much of it, so far, deals with migratory populations over the last tens of thousands of years…
Jacinta: Homo heidelbergensis has struck many palaeoanthropologists as the likely common ancestor of both H sapiens and H neanderthalensis. The Smithsonian dates the species to about 700,000 to 200,000 years ago, but there’s also this from their website:
This species may reach back to 1.3 million years ago, and include early humans from Spain (‘Homo antecessor’ fossils and archeological evidence from 800,000 to 1.3 million years old), England (archeological remains back to about 1 million years old), and Italy (from the site of Ceprano, possibly as old as 1 million years)
Canto: So yes, again, lumpers and splitters, and we’re no experts. From the term Homo antecessor I’d conjecture that they’ve been hailed as direct antecedents…. but other specimens, named H cepranensis, and H rhodesiensis, as well as H heidelbergensis, are in the mix, and the remains are often hard to identify and date, with DNA and the proteins made from them being tricky to isolate from warmer climes…
Jacinta: The Australian Museum gives us this interesting info about H heidelbergensis versus H antecessor, in describing the largest find of specimens:
- The remains of at least 6 individuals found at the site of Gran Dolina, Atapuerca, in Spain. They lived about 800,000 to 1 million years ago in Europe and are the oldest human remains found in that continent. Although many experts consider these remains to be part of an early and variable Homo heidelbergensis population, the discoverers believe the fossils are different enough to be given a new species name Homo antecessor.
Canto: I’m wondering about that Morocco specimen that has recently, no doubt controversially, been reclassified as H sapiens, though it dates from 320,000 to 300,000 years ago, pushing the age of our species back by a hundred thousand years or so.
Jacinta: Yes you’re talking about the finds at the Jebel Irhoud site, and it’s complicated, because most researchers don’t identify that region as the birthplace of H sapiens. They mostly agree that the species was ‘born’ in southern and Eastern Africa. The Smithsonian seems to me a bit confusing and unconvincing on this point:
The remains of five individuals at Jebel Irhoud exhibit traits of a face that looks compellingly modern, mixed with other traits like an elongated brain case reminiscent of more archaic humans. The remains’ presence in the northwestern corner of Africa isn’t evidence of our origin point, but rather of how widely spread humans were across Africa even at this early date.
They’re saying that the oldest human remains found are in north-west Africa, but humans probably originated in south-east Africa, though we haven’t got specimens from there that are older than 260,000 years, at most. Hmmm.
Canto: The paucity of the fossil record is probably to blame. But then – Homo naledi. I’ve just watched John Hawks giving a talk on naledi in 2017 – Hawks is a hero of mine, I used to follow his website regularly – and he talked of more and more discoveries in that diabolical underground cave system called – maybe ironically? – Rising Star, in South Africa. They now have more fossil remains of naledi than of any other ancient Homo apart from neanderthalensis. And they’ve managed to narrow the dating from about 320,000 to 240,000 years ago, from memory. So they may well have lived alongside the earliest H sapiens.
Jacinta: Complexifying the picture in ways some find fascinating, others frustrating. And they were much smaller and smaller-brained, right? Like floresiensis, another mystery. So there will be questions about how ‘advanced’ they were. Is there evidence of tool use? Of fire? And remember, it’s not brain size that matters so much but brain organisation. Think of corvids – tool users, problem solvers, complex family systems, brains the size of a walnut but packed with as many neurons as some monkey species.
Canto: Yes, I agree, we can’t make too many assumptions based on size. Bonobos females are smaller than the males but much smarter, right? But one major difficulty about the naledi lifestyle is that we know nothing about it. It seems these remains were placed, or dropped, in the cave after death. And as far as I know, we have no trace of naledi above-ground, which is kind of bizarre.
Jacinta: Okay, so I’m watching the ever-reliable North 02 vid on naledi. They first thought these remains were probably well over a million years old, due to various features, especially skull size, though there were plenty of anomalies, but they were eventually able to date some of the teeth, using electron spin resonance and uranium-thorium dating, and yes, your dating is about right. As to skull or brain size, smaller than habilis and quite a bit smaller than erectus, but actually larger than floresiensis, which clearly tells us, doesn’t it, that there hasn’t necessarily been this enlargement of brain size over time for all members of the Homo genus.
Canto: Yes, interesting – floresiensis, do we know anything of their lifestyle, tools, decorations…?
Jacinta: The most recent dating of floresiensis has them living until about 50,000 years ago at the latest. So much more recent than naledi. The cave where they were found yielded over 10,000 stone artefacts similar to those associated with the much larger-brained H erectus, from whom they may have learned a few things. With a brain quite a bit smaller than that of H naledi. Surely a cautionary tale.
Canto: Right – and they’re not even looking at brains, they’re looking at skulls, and making possibly unwarranted assumptions.
Jacinta: Okay so there’s a lot more to say on this topic – about Homo naledi alone, never mind the many other species or pseudo-species, so we’ll have to turn this into an ongoing series. I’ve been reading and listening to a lot of very smart people, which has made me feel quite dumb and shallow on the topic – no Dunning-Kruger effect for me at least.
Canto: Well, even as dilettantes we’ve come up with some reasonable skeptical queries – about brain size, and more on that next time, about tool use or the lack of evidence for it, and the lack of evidence of anything re H naledi outside of Rising Star. So, next time…
References
How did humans come to be? DW documentary
D Reich, Who we are and how we got here, 2018
M Böhme et al, Ancient bones, 2020
https://en.wikipedia.org/wiki/Chimpanzee–human_last_common_ancestor
https://humanorigins.si.edu/evidence/human-fossils/species/homo-heidelbergensis
https://australian.museum/learn/science/human-evolution/homo-antecessor/
modern humans are getting less modern, in unexpected places
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://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.
When was the first language? When was the first human?
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
why are our brains shrinking?
my own brain, squeezed of alcohol
Jacinta: So you know that the average human brain mass, or is it volume, has reduced by – is it 15%, I can’t remember – over the past 20,000 years or so, right? And there’s this theory that it’s somehow related to domestication, because the same thing has happened to domesticated animals…
Canto: How so..?
Jacinta: Well, we don’t know how so, we just know it’s happened.
Canto: How do we know this? Who says?
Jacinta: Well I’ve heard about it from a few sources but most recently from Bruce Hood, the well-known psychologist and skeptic who was talking on the SGU about a recent book of his, The Domesticated Brain.
Canto: So the idea is that humans have somehow domesticated themselves, in the same way that they’ve domesticated other species, with a corresponding decrease in brain mass in all these species, which signifies – what?
Jacinta: Well it raises questions, dunnit? What’s going on?
Canto: It doesn’t signify dumbing down though – I read in Pinker’s big book about our better angels that our average IQ is rising in quite regular and exemplary fashion.
Jacinta: Yes, the Flynn effect. Though of course what IQ measures has always been controversial. And they do reckon size isn’t the main thing. I mean look at all those small critters that display so many smarts. For example, rats, octopuses and corvids (that’s to say crows, ravens and some magpies). They all seem to be fast learners, within their limited spheres, and very adaptable. But getting back to the human brain, it seems to be something known mainly to palaeontologists, who have a variety of theories about it, including the ‘we’re getting dumber’ theory, but I’m not convinced by that one. It seems more likely that our brains are getting more organised, requiring less mass.
Canto: So this has happened only in the last 20,000 years?
Jacinta: Or perhaps even less – between 10 and 20 thousand.
Canto: Isn’t that a phenomenally short time for such a substantial change?
Jacinta: I really don’t know. They say it might be partly related to a decrease in overall body size, so that the brain to body ratio remains much the same.
Canto: A decrease in body size? What about the obesity epidemic? And I remember way back when I was a kid reading about how we’d been getting taller with each generation since the Great Depression – or was it the Industrial Revolution? Anyway our improved diet, our era of relative abundance, has led to a change in height, and presumably in mass, in only a few generations.
Jacinta: So now you’re saying that substantial changes can occur in a few generations, let alone 10,000 years?
Canto: Uhhh, yeah, okay, but I wasn’t talking about brain size.
Jacinta: Well why not brain size? Anyway, although there have been those recent changes, at least in the west, the story goes that the planet has warmed since the last ice age, favouring less bulky bodies, less fat storage, more gracile frames.
Canto: So what about domestication, why has this led to decreased brain sizes?
Jacinta: Well this is very complex of course…
Canto: I can think of a reason, though it might not be called domestication, more like socialisation, and outsourcing. You can see it in very recent times, with smart phones – it’s even become an already-stale joke, you know phones are getting smarter so we’re getting dumber. But then we always tend to exaggerate the short-term and the present against the longer view. And yet…. I was on the tram the other night, sitting across from this couple, locked into their phone screens, I mean really locked in, earplugs attached, heads bent, utterly fixated on their little screens, completely oblivious, of each other as well as of the outside world. I was reading a book myself, but I became distracted by my irritation with these characters, while wondering why I should be irritated. It just went on so long, this locked-in state. I leaned forward. I waved my hand in front of their bowed heads. I wanted to tell them that the tram had rattled past all the stations and was heading out to sea…
Jacinta: There are some problems with the whole argument. How do we know that domesticated animals have smaller brains? Domesticated cats have a wide range of brain sizes no doubt, but what wild cats are you comparing them with? Even more so with dogs and their immense varieties. Okay they’re descended from wolves so you compare a wolf brain with its modern doggy-wolfy counterpart, but who’s going to agree on type specimens?
Canto: So you brought the subject up just to dismiss it as a load of rubbish?
Jacinta: Well if we shelve the domestication hypothesis for the moment – I’m not dismissing it entirely – we might consider other reasons why human brains are shrinking – if they are.
Canto: So you’re not convinced that they are?
Jacinta: Well let’s be sceptical until we find some solid evidence. In this Scientific American site, from November 2014, palaeontologist Chris Stringer states that ‘skeletal evidence from every inhabited continent’ suggests – only suggests – that our brains have become smaller in the past 10 to 20 thousand years. No references are given, but the article assumes this is a fact. This piece from Discovery channel or something, which dates back to 2010, relies in part on the work of another palaeontologist, John Hawks, whose website we link to here. Hawks also talks about a bucketload of evidence, but again no references. The original research papers would likely be behind a paywall anyway, and barely intelligible to my dilettante brain….
Canto: Your diminishing brain.
Jacinta: Okay I’m prepared to believe Hawks about our incredible shrinking brains, but is domestication the cause, and what exactly is domestication anyway? Hawks doesn’t go with the domestication hypothesis. In fact the Discovery article usefully covers a number of alternative hypotheses, and of course the shrinking may be due to a combo. In fact that’s more than likely.
Canto: So what’s Hawks’ hypothesis, since we’re supposedly admirers of his?
Jacinta: Well Hawks decided to look more closely at this brain contraction – which is interesting because I was thinking along the same lines as he was, i.e. has it been a uniform contraction, or was there a sudden, quick development, followed by a stagnant period, as you would expect?
Canto: Anyway isn’t brain organisation more important than brain mass? Sorry to interrupt, but haven’t we already established that?
Jacinta: We haven’t established anything, we’re just effing dilettantes remember. Hawks started looking at more recent data, over the past 4000 years or so, to see if he could detect any difference in the encephalisation quotient (EQ) – the ratio of brain volume to body mass – over that time. He found that indeed there has. The picture is complicated, but overall there has been a reduction in the brain compared to the body. His explanation for this though is quite different. He reckons that a series of mutations over recent history have resulted in the brain producing more out of less…
Canto: Right, just as a series of modifications have allowed us to produce smaller but more powerful and fuel-efficient cars.
Jacinta: Uhh, yeah, something like that.
Canto: But we know what those modifications were, we can name them. Can we name the mutations?
Jacinta: Clever question, but we know about cars, we built them and they’ve only been around for a bit more than a century. We know vastly less about the brain and we’re still getting our heads around natural selection, give us a break. Hawks points out that it’s a rule about population genetics well-known in principle to Darwin, that the larger the population the more numerous the mutations, and there was a surge in the human population back when agriculture was developed and large settlements began to form. So a number of brain-related mutations led to streamlining and, as you suggest, fuel efficiency.
Canto: But isn’t this compatible with the domestication hypothesis? I imagine that, if there really is a brain reduction for domesticated animals, it’s because they don’t have to rely on their brains so much for survival, and we don’t either, the collective has sort of magically taken care of it through farming and infrastructure and supermarkets.
Jacinta: Yes but they all have their own complicated networks and issues we have to wrap our brains around. The domestication hypothesis is really about aggression apparently. The argument goes that all animals under domestication become more varied in size, coloration and general build, with a tendency to become more gracile over all. Selection against aggression, according to the primatologist Richard Wrangham, favours a slowly developing brain – one that is, in a sense, in a perpetually juvenile state (think of cute cat and dog videos). Of course, all this assumes that juvenile brains are less aggressive than adult brains, which some might see as a dubious assumption.
Canto: Yes, think of school bullying, Lord of the Flies, youth gangs, the adolescent tendency to extremes…
Jacinta: Well, both Wrangham and Hood offer a particularly interesting example of ‘super-fast’ domestication to illustrate their hypothesis:
In 1958 the Russian geneticist Dmitri Belyaev started raising silver foxes in captivity, initially selecting to breed only the animals that were the slowest to snarl when a human approached their cage. After about 12 generations, the animals evidenced the first appearance of physical traits associated with domestication, notably a white patch on the forehead. Their tameness increased over time, and a few generations later they were much more like domesticated dogs. They had developed smaller skeletons, white spots on their fur, floppy ears, and curlier tails; their craniums had also changed shape, resulting in less sexual dimorphism, and they had lower levels of aggression overall.
Now, how does this relate to juvenilism? Well, in the wild, offspring grow up quickly and have to fend for themselves, which requires a certain ruthless degree of aggression. Cats and dogs, yes, they abandon their offspring soon enough, but those offspring continue to be tutored, tamed, domesticated under their human owners. We hear a lot about school bullying and gangs of youths, but they’re actually the exception rather than the rule, or a last ditch rebellion against the domestication pressure that’s exerted by the whole of society, and they’ll either succumb to that pressure or end up in jail, or worse. It’s a bit like the Freudian concept of sublimation, you channel your aggressive energies into creativity, competitive problem-solving, sports achievements and the like.
Canto: So you’re in favour of the domestication hypothesis?
Jacinta: Well, I’m not against it. It sounds plausible to me. Human domestication, or self-domestication if you want to call it that, is a social-contract sort of thing. You agree to outsource and comply with certain arrangements – laws, government, taxation and so forth, in return for certain benefits in terms of security and resources. So you don’t have to fend for yourself. And that affects the brain, obviously. Though it might not be the whole story.
the biggest dinosaur?
Okay I was going to write about the intriguing and tragic figure Ludwig Boltzmann, in keeping with my plan to write connected pieces, but today’s ‘wow’ news reports about ginormous dinosaur bones found in Argentina – already the domain of the largest dino ever found, the sauropod Argentinosaurus – have proved just too irresistible. Ludwig will have to wait. I learned about Argentinosaurus earlier this year while researching dinosaurs for another post, but this recent discovery is of what’s believed to be a new species of titanosaur or giant herbivore. You’ll see pics of the giant thigh bone all over the net, usually with some dusty palaeontologist or farm worker snuggled against it, but scientists are cautioning against too much speculation about this beast’s proportions in comparison to that of Argentinosaurus, from the relatively scant remains found so far. We do love to see records broken, don’t we? In any case the animal’s femur looks like taking the record of biggest bone ever found.
Of course, even if this unnamed beastie was 77 tonnes, as some pundit has calculated it, compared to 70 tonnes for Argentinosaurus, that doesn’t prove that one species in general was larger than the other. Argentinosaurus’ weight has been based on even more scant remains. Take a look at a range of websites, including Wikipedia’s entry on dinosaurs, and you’ll find quite a range of values for the weight of Argentinosaurus. It’s not quite wild speculation, but it’s speculation nonetheless. I’m also wondering, from my profoundly non-expert perspective, if these bones from what is now Argentina reveal the limited range of those creatures or if they’re largely a result of a combination of the right kinds of preservatives – soil type, climatic conditions and so forth – prevailing in that region.
It’s a great time for dinosaur fans. A new species of long-snouted tyrannosaur, named Pinocchio rex, has recently been unearthed, ‘remarkably well-preserved’, in southern China. It’s estimated to have lived about 66 mya, in the late Cretaceous, the last period of the dinosaurs. Not quite the size of T rex, it may have been faster and nimbler. One expert described it as a cheetah to T rex’s lion, because the two tyrannosaurs lived and hunted in the same regions, chasing different prey.
Our new Titanosaur also hails from the Late Cretaceous, though probably earlier than P rex (the Late Cretaceous extends more than 30 million years, from 100 to 66mya).
Incidentally, the record for the smallest dinosaur goes to a birdie from 120 mya called Quiliana, weighing in at 15 grams. Well, that’s according to this site. Wikipedia describes the smallest dinosaur as weighing about 110 grams and measuring about 35 cms but they don’t include ‘avialan’ dinosaurs (i.e. birds). In fact, just about every site I’ve checked out describes a different species. But if you accept, as many do, that birds are dinosaurs, then the smallest dinosaur ever is still with us. The bee hummingbird is only about 5 centimetres long and weighs about 2 grams.
who fought who in the upper cretaceous?
Pachyrhinosaurus
So here I am at lovely Victor Harbour on Encounter Bay where England’s Matt Flinders and co encountered France’s Nick Baudin and co most unexpectedly over 200 years ago as each expedition was sailing round this great south land in opposite directions, mapping and exploring and discovering, but I’m not going to tell that story, I’m going to explore a much earlier era, as we spent a little over an hour in the heat of the day in the local cinema, watching a thing called Walking with dinosaurs – the movie. I think this was a companion-piece to Walking with dinosaurs – the real thing, or something like that. Anyway, it was aimed largely at kids, with a horribly anthropomorphised storyline replete with Yank cliches, in Yank accents, in spite of its being a BBC production. The animation was fine though, and hey it was dinosaurs, so more or less bearable.
But what about historical accuracy? Wouldn’t want to be leading kids up the garden path. The story, we’re told, takes place 70mya, in what’s now Alaska. Our hero starts life as the runt of the litter, and of course ends up as the leader of a herd of hundreds if not thousands. He’s a pachyrhino or something, and they headbutt for control of the females, and other males, and have to fight off their natural predators, the omnivorous gorgosauri. He also at one stage gets adopted by a wandering herd of gigantic edmontosauri, a herbivorous bunch. I’m no dinosaur expert but I’ve never heard of any of these beasties, whose names are presented to us with an air of scientific authenticity.
Well, as it turns out they’re all quite real (what was I thinking, BBC and all). Gorgosaurus (‘fierce lizard’) is known to have roamed about the region of modern Alberta, Canada some 75mya (the late or upper Cretaceous). Weighing in at more than 2 tonnes, it was an apex predator, a genus of tyrannosaurid therapod dinosaur, and is one of the best-represented tyrannosaurid therapods, with dozens of specimens found, so shame on me for my ignorance. Smaller than Tyrannosaurus, to which it’s distantly related, it’s often confused with Albertosaurus, and they may simply be variants. As with all tyrannosaurids, its massive head is crammed with teeth, though not so many, and not so blade-like, as T rex. The Wikipedia article on gorgosaurus is incredible detailed and overwhelmingly rich for dilettantes comme moi, but it’s well worth a visit.
Gorgosaurus libratus
The protagonist of the movie was a Pachyrhinosaurus. They inhabited the Alberta and Alaska regions from 79 t0 66mya. They’re a genus (of which 3 separate species have been recognised) of centrosaurine ceratopsid dinosaurs. They were gentle giants (when they weren’t headbutting), weighing up to 4 tonnes, and their presentation in the film as herd animals is backed up by the most important find of pachyrhinosaurus fossils, a bone-bedalong Pipestone Creek in Alberta, where some 3500 bones and 14 skulls have been found, apparently the site of a mass mortality, possibly a failed river crossing.
Pachyrhinosaurus has become a popular dino since being relatively recently discovered, in the forties. I’ve mentioned it’s a centrosaurine ceratopsid, the centrosaurinae being a subfamily of ceratopsid dinosaurs (which doesn’t include Triceratops, the most well-known ceratopsid). The centrosaurines are divided into two tribes, the centrosaurins and the pachyrhinosaurins. Ceratopsids all have these fearsome-looking great horny heads, like elephantine frill-necked lizards, but they’re all quadrupedal herbivores, so not only are we safe from being eaten by them, we might be able to eat them ourselves if we could bring them back to life. And I’m sure their horns would have aphrodisiac qualities.
The other dinosaur type featured, Edmontosaurus, was a hadrosaurid or duck-billed dinosaur, some 12 metres long and 4 tonnes in weight. There are two known species, one of which is known to have lived right up to the Cretaceous-Paloegene extinction event (the one that killed off all non-avian dinosaurs). They were coastal-dwelling herbivores, from North America (so-named because first found near modern Edmonton), and if the general rule is – and I’m largely guessing here – that the herbivorous dinos roamed about in herds, like modern-day bison, antelopes and kangaroos, then the scenario in Walking with dinosaurs, in which our young pachyrhino and his bro hook up with a herd of edmontosauri for a while, and were savaged by scavenging is almost plausible for the time and place.
So, with the help of Wikipedia mainly – it’s very comprehensive on this stuff – I managed to get quite a lot out of Walking with dinosaurs, though I have to say, some of it was strictly for the birds.
Should we be lumpers or splitters over our hominid ancestors?
D4500 on the right
As I’m overwhelmed and a bit stressed by work issues, I’ve not posted here for a while, or to be precise I’ve got three or four posts going which I’ve not been able to finish. So I’ve decided to throw something down and push it out today no matter what.
A fascinating post on the John Hawks blog, alerted to me by Butterflies and Wheels. He goes into much detail on an issue that has fascinated me, in my dilettantish way. My general reading on human ancestry, which turned up names such as Homo erectus, Homo habilis, Homo ergaster, Homo rudolfensis, Homo heidelbergensis et al, together with the information that the remains of these hominids or hominins were scanty and their precise identities disputed, made me wonder from my distant armchair whether they all represented different species or just variants of the one. Of course I have no expertise at all, and I don’t know the difference between a species and a subspecies, but my reading did make me aware that this was a genuine issue amongst paleoanthropologists.
The Hawks post, which takes its departure from a paper published on a recently revealed specimen of Homo erectus, goes into some detail on all this. The cranial specimen, D4500, from Dmanisi in Georgia, is the best-preserved of any so far discovered. The writers of the paper take the opportunity to put forward the view that the early Homo finds, such as D4500 and remains from the Malapa fossil site in South Africa, and by inference a number of others, represent a single lineage, a view with which Hawks largely concurs. So there, I told you so.
Of course Hawks goes into a lot of detail, and expresses his views with the diffidence we generally find in true scientists, but I’m delighted to find my vague sense of things so thoroughly supported. i must be a lumper, but of course I’m prepared to change my mind at the slightest change in the winds of research. Now I just need to work out where all those Australopithecines fit into the general picture, without moving too far from my armchair, of course.