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Human evolution: fossils surprising, fossils predicted
Paper presented by Professor Colin Groves
National Museum of Australia, 26 February 2009
ROBYN WILLIAMS: Two quick comments on what we heard this morning. One of them is on Origins. There is a very nice doctor who lives in Louisa Road, Balmain called Dr John Collie, a friend of mine, who once wrote a movie for Peter Weir called Master and Commander starring some Russell chap. He’s now written a book [movie] called Origin with Paul Bettany playing Darwin and Elizabeth Connolly playing Emma. The shooting finished at the end of 2008. They are into post-production and with any luck it will be out in the not too distant future. John Collie does a wonderful script and he understands the science. It is based on the book Annie’s Box by Randal Keynes.
I had another person to do with the movies [on my show] on 14 February, a fellow called Matthew Chapman who is a great-great-grandson of Charles Darwin and who writes movies for Bruce Willis, Dustin Hoffman and Victoria Tennant - in fact, he used to be married to Victoria Tennant. He grew up in Cambridge but then saw the light and became a rather productive writer of feature films. The movies are progressing. Another one is supposed to be done by Fred Schepisi produced by Penny Chapman whose two biographies of Darwin you may have seen on SBS two weeks ago. So much for the background and the movies and Hollywood.
This afternoon, in the final sprint towards 3 o’clock when we will have some Q&A, is presented by Bernadette Hince who is a dear friend of mine. She’s a historian and lexicographer. She is a visiting fellow at the Australian National University’s Dictionary Centre. Her main research interests are on the history and words of the Polar regions. She has written The Antarctic Dictionary: a complete guide to Antarctic English, something every household needs because you can look up the word ‘snotsicle’. You probably don’t need to. Only in Antarctica could that be a compelling word. The other thing you need to know about Bernie is that she’s a fabulous cook and as far as I know is the world expert on Emma’s own cooking style. So you can ask her questions about that. Bernie, would you please chair the afternoon.
BERNADETTE HINCE: Thank you very much, Robyn. Welcome to the afternoon session. We have three very different speakers from diverse backgrounds to talk about Darwin’s legacy. First of all we start with Colin Groves, professor of biological anthropology here at the Australian National University. Colin is going to talk to us on ‘Human evolution: fossils surprising, fossils predicted’. Thank you, Colin.
COLIN GROVES: Darwin had this one enigmatic sentence in the Origin of Species about the possibility of human evolution, but the man who put it centre stage was Thomas Huxley. In 1863, he wrote a paper, which was based on a lecture which he had given, called ‘Man’s Place in Nature’. He compared human and ape skeletons with a vaguely evolutionary slant on it and he introduced a very important idea in it: the missing link. He said:
Remember, if you will, that there is no existing link between Man and the Gorilla, but do not forget that there is a no less sharp line of demarcation, a no less complete absence of any transitional form, between the Gorilla and the Orang, or the Orang and the Gibbon.
1863 is the first outing of human evolution after Darwin – ‘existing link’. The person who actually put the two words ‘missing’ and ‘link’ together was Hugh Falconer. Falconer had discovered an unusual human skull in Gibraltar in 1848. He was a friend of Darwin. He was impressed - I don’t know whether he actually accepted Darwinian evolution - but certainly he was well disposed towards it. He compared the Gibraltar skull to a similar skull discovered in Germany in 1856 from the famous Neanderthal, the valley of the hymn-writer Neander. Falconer wrote to a relative, and this was published posthumously after his death in 1868:
If you hear any remarks made, you may say from me, that I do not regard this priscan pithecoid man as the ‘missing link’ so to speak. [The first mention of this phrase in print] It is a case of a very low type of humanity - very low and savage, and of extreme antiquity - but still man, and not a halfway step between man and monkey.
At once he is introducing what is now a much-misused catch phrase. He is bringing for the first time fossils into the story of Darwinism and he is also beginning to treat fossils quite seriously as possible elements in the Darwinian story.
So now let’s go forward one century. What’s been happening in discoveries of fossils in the human lineage since then? We have Australopithecus africanus. This as we now know, but was not known at the time of its discovery, is two-plus million years old. It has an endocranial volume - that means volume inside the brain case - of 440cc which is about a third of the average of ourselves. It has small canine teeth, not large ones like an ape. It has the pelvis of a biped but it is still not completely modern. There are details in which it is not completely modern in its bipedal form. There is a picture of a skull of it, and there is an innominate bone (half a pelvis) [shows image].
Then we knew of Australopithecus (or Paranthropus - most people now refer it to a different genus Paranthropus) robustus and boisei, which are sometimes called ‘robust Australopithecines’. These are one to two million years old and are definitely a sideline. Everybody, with a couple of exceptions, admits now that that is the case - that we do have at least this one sideline in human evolution. These are skulls of them [shows image] - big robust things with crests on their heads and huge, huge jaws but flat faces.
Then we knew of Homo erectus which was discovered in Java in 1891, and other specimens have been discovered since then. This we now know ranges in age from about half a million to over a million but the exact dates at either end are still under discussion. The endocranial volume of this is 1000cc, so it is getting up well up towards the modern human range; and it has unexpectedly large brow ridges - there’s a brow ridge for you! [shows image].
And then Homo sapiens with an average cranial capacity about 1300cc (but extremely variable of course).
How human evolution looked in about 1960 was like this [shows image]. There is a stem, AA is Australopithecus africanus. There is a single branch Australopithecus robustus (boisei being related) and then the stem goes on up to HE, Homo erectus and HS, Homo sapiens. That is how it looked then.
Then we expect to find an intermediate between Australopithecus africanus, the supposed ancestor, and the next stage up supposedly Homo erectus. So it was expected to find this intermediate and it was found in 1964. It was described as a new species, Homo habilis. For the first time radiometric dating was applied to the site where it was found, Olduvai Gorge, and it was found that the specimens referred to as Homo habilis were between 1.6 and 1.8 million years old and the endocranial volume, the cranial capacity, was 650-680cc - nicely intermediate between Australopithecus africanus and Homo erectus. The foot, to quote Day and Napier, ‘indicates that bipedal walking had achieved an almost modern degree of advancement’. A nice foot skeleton was found along with all these jaws and skull fragments.
In fact, it was so intermediate between Australopithecus africanus and Homo erectus that many commentators - there are always people who are trying to put their own oar in and put their own spin on what has been discovered - didn’t accept Homo habilis as the expected intermediate species. Why not? The answer is it was considered by some that some of the specimens referred to it should actually have been classified as ‘advanced Australopithecus africanus’ and the others as ‘early Homo erectus’. These people were having a bob each way - they are intermediate, but not a new species.
How human evolution now looked was like this [shows image]. There’s the new species HH Homo habilis on the bottom right, intermediate between Australopithecus africanus and Homo erectus. You see still a nice steady evolution onward and upward, branching off at one point but essentially going from then to now in one single branch.
Then came some surprising fossils - Australopithecus afarensis. Everybody had been very happy with Australopithecus africanus until this was discovered; and it’s early - 3.0 to 3.7 million years from a site at Hadar, Ethiopia and a site at Laetoli, Tanzania. The cranial capacity was slightly less on average than Australopithecus africanus. The find included some very well preserved fossils. The famous fossil ‘Lucy’ - there’s her skeleton on the far right [shows image] - was discovered at Hadar, and a series of fossils all found together thought at the time to have been part of a single social group and known as the ‘First Family’. There were abundant other, more fragmentary, remains from Hadar. Laetoli had only some rather fragmentary remains, jaws and a fragmentary skeleton, but did show footprints embedded in volcanic ash. There is one illustrated there [shows image].
Why was this surprising? For a number of reasons: first of all, as I said everybody had been satisfied with Australopithecus africanus, but this put a new light on it. It is the first time the long time-span is mentioned. People thought evolution was steady and gradual - Darwin had almost said as much. In fact, Huxley had twitted him on it: ‘I think you are unwise to have rejected the idea that nature makes no leaps.’ And of course if nature makes leaps, then before and after the leap there must be stasis, a period of relative calm when there is little or no change. Indeed, Australopithecus afarensis had a very long time span when very little did appear to happen within it, a period of stasis. The species was widely distributed: Ethiopia and Tanzania are some 2000 kilometres apart. It had great sexual dimorphism; nobody had expected that one of our perhaps-ancestors had huge males and tiny females. And some of the facial features resembled Homo, suggesting that Australopithecus africanus was actually too specialised to be ancestral to Homo - surprising but adding a cog to the story of human evolution.
Here is how human evolution now looked [shows image]. Now you see that Australopithecus africanus has been pushed off into a side branch. But of course we must have, many people were saying, relatively few branches because after all humans are special so they must have evolved in a special way. It was still essentially onward and upward and still the one side branch, but now Australopithecus africanus has joined the robust ones on the side branch. There is Australopithecus afarensis on a now rather lengthened stem leading up to the split, and on the right-hand side of the split we still have Homo habilis, Homo erectus and Homo sapiens.
Fossil expected - well of course we have these ‘robust Australopithecines’, Paranthropus, but they need an ancestor too. Australopithecus africanus maybe, but quite suddenly we have something different. Remember that Paranthropus is one to two million years old. As I pointed out it had these huge jaws and teeth, massive check bones, sagittal crest and very flat foreshortened face - very odd-looking creatures indeed. They need an ancestor. What would you predict from this ancestor? Well, perhaps something with more jutting jaws like Australopithecus africanus and Australopithecus afarensis… and one turned up. It’s of the right age - 2.5 million years old - to be an ancestor of Paranthropus. It looks almost exactly like later Paranthropus but with a protruding snout. So we have given them an ancestor - entirely predictable. A great fuss was made when this ‘Black Skull’ was discovered; I am not sure why, because I think it was entirely to have been predicted.
More fossils expected - we can now go back in time. Australopithecus afarensis had now liberated us from the idea that we must have as short an evolutionary span as possible. We can now look backward, and what comes before that? Australopithecus anamensis, then a genus called Ardipithecus and then finally one called Orrorin. These go back to almost six million years of age. Admittedly these three are all still rather fragmentary in the fossils that we know about them, but we are beginning to get back towards the split with our nearest ape relative, the chimpanzee. [shows image] You can see in the middle, with Ardipithecus, relatively longer canines than we have seen in humans and Australopithecines, not as long as in apes but certainly getting back towards intermediate stages with apes, especially with chimpanzees. The fossils that one had expected and now predicted - there they turned up.
And more that were expected - going forwards. We have Homo ergaster found in Kenya between 1.8 and 1.5 million years, again a bit of stasis. When we compared it with Homo erectus, one of its successors, we saw smaller brows and less flattened brain case. There is a beautiful, nearly complete skeleton of an adolescent on the right [shows image], the so-called ‘Turkana boy’. What this did - but people were prepared for it now: Australopithecus africanus had been pushed off the main line - and now maybe Homo erectus. It was surprising to a lot of people that Homo erectus had these huge brow ridges and very thick, flattened skull, and Homo ergaster wasn’t quite like that. It did show that Homo erectus is more specialised and is unlikely therefore to be a human ancestor, as we had more or less deduced already. So it wasn’t too surprising by now, given the previous context.
And also more fossils that were expected - Homo heidelbergensis. Actually a lot of fossils had been discovered in the meantime, mostly rather fragmentary fossils, both in Europe and Africa between about one million and 300,000 years ago. Better specimens now began to turn up, and we began to see that these were all very much of a muchness. Maybe here, instead of having a lot of fossils preserved at one site which one could be fairly certain were all of the one species, perhaps we have a lot of fossils widespread - over Europe and Africa in this case - but all rather looking alike. The favourite hypothesis at the moment is that these are all one species which we name after the very first of them to be discovered: the Heidelberg mandible, which is illustrated there next to the bottom right [shows image]. That was discovered in 1908. It has now proved to have been the first specimen of this later species. So the story is gradually going on and on.
Everybody was very happy. We now know what happened in human evolution. Nothing will surprise us any more. Is that so? First, there is Homo georgicus. A jaw was discovered in 1993 and then a series of skulls and one skeleton from 2000 until the present day. These were intermediate between Homo habilis and Homo ergaster. Wonderful - we had expected to find an intermediate. But the surprise was where they were found. Human evolution took place in Africa, didn’t it, until finally there was the great leaving of Africa. There were at least two great leavings of Africa, but that’s the locus of human evolution.
Homo georgicus was found not somewhere in Africa but in a cold climate in the Republic of Georgia at the foot of the Caucasus - ‘at the gates of Europe’ as somebody put it. What were our ancestors doing there? Homo habilis out of Africa to become Homo georgicus, back into Africa to become Homo ergaster. It is all very strange but here are the specimens. You can see they are wonderful specimens [shows image]. With one of them, when it was discovered the film of its discovery was put immediately on the web so you could watch them scooping it out and uncovering it and pulling out the new skull and then pouring champagne.
So around the year 2000 this is how human evolution was looking. It is not onward and upward any more. We don’t have some just-not-ape scanning and looking at the distant horizon and thinking ‘I am going to get there, I am going to invent television sets.’ Instead we have lots of side branchings, things becoming extinct, things surviving - things telling me that I have only one minute left [looks nervously at Bernie, signalling madly at him]. The human evolutionary tree actually looks much more like other well-known African animals of which we have a good fossil record. The two ‘ancestors’ of the 1960 tree are both sidelines. There they are in red [shows image]. So that is a bit surprising.
In 2000 more surprising fossils were discovered. Look at this magnificent skull of Sahelanthropus tchadensis that was discovered in Chad, West Africa. What is it? How could anybody possibly still be debating what this wonderful specimen of a skull is? According to faunal comparisons with dated sites in East Africa - you can’t date a stable site, or not yet, like Koro Toro - you have to have a volcanic site like the East African sites. But by comparison with fauna at dated East African sites, it is six to seven million years old which is about the age, according to the molecular clock, when we split from chimpanzees. So what is it? It is distorted - there is a mandibular fragment, a few isolated teeth. That’s it. It has a very small cranial capacity, huge brow ridges, huge sagittal crest. It is a straight not protruding face and the point of balance seems fairly far forward, but it is distorted so I am not convinced of that myself. Short canines apparently, but what sex is it? Females have smaller canines than males anyway. What are its affinities? It could be at the base of the human stem, the base of the chimpanzee stem, even perhaps the base of the gorilla stem or perhaps part of the common ancestral stock. I don’t know yet. It’s a completely open question.
And finally fossils surprising - absolutely astonishing, so astonishing that people have gone right back to the beginnings – there is Homo floresiensis, found in Flores, eastern Indonesia. It looks like a little Australopithecine, doesn’t it? But the remains are scattered throughout the Liang Bua sequence. They are from 75,000 to 12,000 years old - where is all these millions of years? What’s an Australopithecine doing so recently? There is a fairly complete skeleton called LB1. There’s a second jaw LB6 with some associated post-cranial parts, isolated bones and teeth. It was one metre high, tiny little thing, low cranial capacity in the Australopithecine range. It has brow ridges, protruding jaws, no chin. It is not just no chin - a lot of people probably here have no chin - but it is internally buttressed like an ape or like an Australopithecine. And that’s different. It is not just a matter of being chinless. The shoulder joint has now been analysed. It lacks the rotatory ability of Homo sapiens. The wrist bones lack the full degree of expansion and contraction, specialisation of Homo sapiens. Short legs, long feet - very controversial.
Here is a couple of hypotheses about it [shows image]. The lower one is the one which I am definitely inclined to support. It’s a long isolated direct descendant of something like Homo habilis. So there was an earlier dispersal from Africa which reached Indonesia and somehow got across to Flores, which is east of the so-called Wallace’s line. Whether that existed then, I am not absolutely sure. That is what seems most likely to me. The search must now be on for what its ancestors were, where it came from.
Every one of the really surprising fossils has been vigorously denied. When the Neanderthal skull was first announced and brought in to the scheme of human evolution by Huxley and Falconer, they said it was a poor idiot. They said it was due to horse riding that it had these curved thigh bones. Rudolph Virchow who was no slouch - he was the founder of the field of paleopathology - invented a life history for this poor skull. When Pithecanthropus, which we now know as Homo erectus, was discovered, this too was thought to be anything but something intermediate between human and ape. Daniel Cunningham, a noted medic at the time, said it is unquestionably human whereas Virchow, who was still alive at that time, said no, it’s a giant gibbon. When one says it is human and the other says it’s a gibbon, something suggests to me it might be ever so slightly intermediate. Australopithecus africanus was disputed as well by the contemporaries when that too was discovered.
So why not, in the grand old tradition of denying a surprising fossil, look at what they have said about Homo floresiensis. Jacob et al. said that it is drawn from an earlier pygmy Homo sapiens population but individually shows signs of a developmental abnormality, including microcephaly. That’s a condition where people are born or develop with abnormally small brains - 400cc would be extremely small though not absolutely unknown. ‘Microcephaly’ says Bob Martin. ‘A general growth hormone defect,’ says Gary Richards. ‘Laron Syndrome,’ says Hershkovitz et al. A ‘cretin’, says Peter Obendorf at al. Cretins are people with iodine deficiency who develop with small size and usually fairly small brains but not like this. So what will next week’s pathology be, I wonder? They keep coming up with these things, everything except what is staring them in the face. Or as T.H. Huxley put it in 1890, when he commented on the denialists’ reaction to the Neanderthal discovery:
It could be and it was suggested that the Neanderthal skeleton was that of a strayed idiot; that the characters of the skull were the result of early synostosis or of late gout; and, in fact, any stick was good enough to beat the dog withall.
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Date published: 30 April 2009