Across all the natural sciences no subject has stirred up more controversy over the last 150 years than that of the evolution of our own species, Homo sapiens.
Much of that controversy stems, of course, from the corrosive impact of the neoDarwinian synthesis on religious beliefs relating to the origins of humanity and the presumption that our species occupies a special, divinely-favoured/ordained place in the universe but it has to remembered that not all of disputes and controversies that have arisen from the study of hominid evolution have been rooted in religious belief.
Much of the early development of the science of paleoanthropology, during the second half of the 19th century and the first half of the 20th, was driven by the search for the much-fabled – and fallacious – ‘Missing Link’* between Homo sapiens and the primate ancestors we share with our closest living relatives, the Chimpanzee and the Bonobo – although the latter was not discovered until 1928 and accorded the status of a distinct species in 1933. Although early proponents of evolutionary theory took the view that humans were likely to have originated in Africa, based on the assumption that morphological similarities between ourselves and the African great apes, the Chimpanzee and Gorilla, suggested that common ancestor would be found in or close to their natural range; reports of fragmentary hominid fossils being sold by Chinese apothecaries as ‘dragon bones’ led to Asia becoming the primary focus of the search for evidence of ancestral hominid species.
* Chapters 6 and 7 of Richard Dawkins ‘The Greatest Show on Earth’ pick apart the fallacious reasoning that to often accompanies talk of ‘missing links’ and intermediate/transitional fossils with chapter 7 dealing specifically with the paleoanthropological evidence for hominid evolution.
The search for early hominid fossils in China and South-East Asia produced the earliest known examples of Homo erectus, most famously in the form of ‘Java Man’ and ‘Peking Man’, and in conjunction with its African contemporary/counterpart, Homo ergaster spawned a series of taxonomic and theoretical disputes over precedence that have yet to be fully settled. Homo ergaster/erectus, according to one theory, evolved in Africa and migrated from that continent to the ‘Old World’ (Europe & Asia) around 2 million years ago, spreading as far as India, China and Java by around 1.3 million years ago. Under this theory, Homo erectus is an alternative name for Homo ergaster, i.e. they’re the same species, or a descendent o Homo ergaster, placing it on the same ancestral line of descent as Heidelberg Man (Homo heidelbergensis), which lived 400,000 – 600,000 years ago, Neanderthal Man (Homo neanderthalensis or Homo sapiens neanderthalensis) and our own species, Homo sapiens.
The alternative theory holds that Homo erectus evolved in Asia as a separate species to Homo ergaster and migrated in the opposite direction, to Africa, although the evidence for this rather sketchy. Early hominid fossils have been found in both China and the Caucasus (Georgia), the latter with a number of stone tools, both of which predate the earliest evidence for Homo ergaster (Turkana boy) and both were initially identified by some scientists as examples of Homo erectus. However its now thought that the Chinese fossil, Wushan Man, is actually that of a previously unknown non-hominid ape while the Georgian hominid, dubbed Homo georgicus appears to be an intermediate which falls in between Homo habilis and Homo ergaster/erectus, making this a possible ancestor of the Asian Homo erectus.
The moral of the story is that reconstructing the history of hominid evolution from the often fregmentary evidence we have to hand is far from being a straightforward business – unlike the Bible, there’s no easy list of ‘begats’ to work with, let alone two largely contradictory lists, which is what the New Testament actually contains. That said, the discovery of Homo erectus in Asia resulted in theories which proposed an Asian origin of Homo sapiens to predominate during the first half of the 20th century, only for these to be overturned between 1950 and 1970 thanks to the work of Richard Leakey and others and the discovery of earlier hominid and, particularly, australopithecine fossils in sub-Saharan Africa.
Today, its generally accepted that Africa is a ‘cradle of humanity’ and, in regards to our own hominid species, the dominant current theory holds that homo sapiens evolved in Africa around 200,000 years ago and that one branch of that species migrated from Africa to Asia via the coast of what is, today, the Arabian peninsula at some time between 125,000 and 60,000 years ago, reaching full behavioural modernity around 50,000 years ago. As these first anatomically modern humans spread across the planet its thought that they encountered and out-competed other, more ancient, hominid species – notably the European Neanderthals – to become the dominant species on the planet, although some scientists argue that, based on genetic evidence, that the is also evidence of interbreeeding with Neanderthals such that modern humans share about 4% of their DNA with their long extinct ‘cousins’. It has also been thought, for some time, that these same migrant humans may also have encountered and similarly out competed surviving populations of Homo erectus and they colonised Asia, although the evidence for this is extremely limited. A single fossil of the upper cranium of Homo erectus (NG6) was discovered in Indonesia in 1931 and dated at between 27,000 and 53,000 years old and, in 1996, a number of late Homo erectus sites and Ngandong, Sambungmacan and Jigar were dated to between 35,000 and 50,ooo years old.
This is the ‘Out of Africa’ hypothesis and it is not without its detractors. Some scientists, notably Milford Wolpoff, argue for an alternative multi-regional origins theory which argues that humans evolved as a species, in Africa, 2 million years ago but that subsequent evolution via archaic hominids, such as Homo erectus, through to Homo sapiens should be viewed as the development of single human species which occurred simultaneously in different regions, including Asia, Europe and Australia, via a combination of regional adaptations and gene flow between regions. An earlier proponent of multiregional theory, Franz Weidenreich, proposed, early in the 20th century, that Peking Man, a fossil Homo erectus discovered in 1891, was the direct ancestor of the Chinese race, a view that took hold in China where it rapidly became bound up in Chinese Nationalism as – allegedly – evidence of their own separate and unique development for that of the rest of the species. This view was largely debunked by a study published in 1999 by Chinese geneticist Jin Li who demonstrated that genetic diversity within the modern Chinese population was well within the bounds of that of global population, supporting the view that there was no interbreeding between early human migrants from Africa and an ‘indigenous’ Homo erectus population, a result consistent with the recent single origin, i.e. ‘Out of Africa’ hypothesis. To confuse matters further, however, a study of RRM2P4 gene data published in 2005 suggests that the Chinese, although descended from an African population, does appear to show evidence of hybridisation with older Eurasian populations with an estimated divergence time of 2 million years ago; around the time of the emergence of Homo ergaster/erectus and a result which offers some support to a limited form of the multi-regional origins hypothesis, albeit that the researchers were suitable cautious is presenting their findings:
The distribution of the Asian lineage strongly suggests an Asian origin but should not be taken as definitive proof that it did not originate in Africa.
Given the complexity of the evidence, this is not the kind of territory into which a tabloid or mid-market newspaper would be advised to insert itself, but this is nevertheless precisely what the Daily Mail did only yesterday in a piece which carried the ‘Daily Mail Reporter’ byline, which is surely the clearest possible indication that the article is being churned directly from either a press release or wire copy by a journalist who is entirely unqualified to even research the story let alone validate its conclusions:
An ancestor of modern humans may have became extinct earlier than was previously thought, throwing doubt on a key theory of human evolution.
Homo erectus, widely considered to be a direct ancestor of our own species Homo sapiens, migrated out of Africa around 1.8 million years ago.
By around 500,000 years ago it had vanished from Africa and much of Asia, but until now was thought to have survived in Indonesia until as recently as 35,000 years ago.
Early modern humans reached the region about 40,000 years ago, and so were believed to have co-existed with their ancestors.
The new research suggests this assumption was wrong, and Homo erectus disappeared long before the arrival of Homo sapiens in Asia.
Fortunately, the full paper is available via PLoS One, so we can check the Mail’s churned interpretation of its contents against what it actually says, and from paragraph 2-5, the Mail is right on the money. The paper, by Indriati et al. does indeed reassess the dating evidence for the late Home erectus sites at Ngandong, Sambungmacan and Jigar and its does arrive at a very different date, on which suggests an age of at least 143,000 years old rather than the 35-50,000 which suggested that the local Homo erectus population may have been around at the same time as Homo sapiens. This also, of course, calls in serious question the dating of the NG6 fossil which, again. seems likely to be rather older than was previously thought.
Where the Mail gets it completely wrong is in suggesting that this paper necessarily throws doubt on the validity of the ‘Out of Africa’ hypothesis, which it doesn’t, not least as it goes on to add that:
New excavations and dating analysis indicate that Homo erectus was extinct by at least 143,000 years ago, and perhaps more than 550,000 years ago.
If this is the case, it challenges the widely accepted ‘Out of Africa’ hypothesis which holds that modern humans became fully evolved in Africa before emigrating to other parts of the world.
The model predicts an overlap between Homo sapiens and older species they replaced outside Africa.
The late survival of Homo erectus in Indonesia had previously been held up as evidence supporting the theory.
Before pulling up the multi-regional hypothesis:
An alternative ‘multi-regional’ hypothesis proposes that modern humans evolved from ancestor species in Africa, Asia and Europe.
The problem is that the ‘Out of Africa’ hypothesis is in no sense dependent on there having been a Homo erectus population living in Indonesia around 35-50,ooo years ago. With or without Homo erectus in situ, a migratory population of Hom sapiens would have moved into and colonised the area, much as happen in both Australasia and the Americas. So far as Homo erectus is concerned all the revised dating evidence tells us is that whatever it was caused its extinction, we can be pretty sure that it wasn’t our most direct ancestors.
This does leave us with an interesting question in regards to the genetic evidence relating to the RRM2P4 gene in the Chinese population, if one take they view that this indicates some degree of limited interbreeding between the ‘Out of Africa’ population and an archaic hominid population that was already indigenous to Asia at the time of the migration but there are other possible explanations for this that do not rely on Homo erectus being a contemporary of Homo sapiens, the most obvious of which – given what we know of Europe and both Homo heidelbergensis and Homo neanderthalensis – being that the hominid fossil record from Asia is currently incomplete and that there may well be one of more as yet undiscovered archaic hominid species out there which provide the same temporal ‘bridge’ between Homo erectus and Homo sapiens that Homo heidelbergensis and Homo neanderthalensis provide in Europe.
Interestingly, the Dali skull, discovered Shuntang Liu in 1978, has been dated at 200,000 years old and differs sufficiently from that of Homo erectus to suggest that it may well be that of as yet unknown archaic homo sapiens, one which has the appearance of an intermediate between Homo erectus and homo sapiens but one unrelated to the Neanderthals. Similarly, the Denisova hominin, which has been dated to 41,000 years old, has been found to share a common origin with then Neanderthals and to share between 4-6% of its DNA with modern Melanesian populations in Papua New Guinea and the Bougainville Islands and is thought, from this, to have ranged widely across Eastern Asia.
What this suggests in not that the ‘Out of Africa’ hypothesis is wrong but that its as yet incomplete and that there are layers of complexity still to be discovered. Moreover it paints a picture of or distant ancestors not as genocidal maniacs wiping out any and all hominid species that dared to cross their path but as behaving much more after the fashion of more recent colonists who not only conquered new territories without wiping out entirely the indigenous population but, in some case, interbred with the locals, producing hybrid offspring. This implies that the infertility barrier, which is generally accepted as one of the hallmarks of full speciation, was not quite so complete in respect of other archaic hominids to whom we were, perhaps, more closely related than some might have previously supposed but what it doesn’t demonstrate -as yet – is that Homo sapiens evolved anywhere on the planet other than in Africa or that it left Africa any earlier than is thought to be the case by proponents of the ‘Out of Africa’ hypothesis. For this hypothesis to be genuinely called in question, what would be required is evidence of Homo sapiens living outside Africa before the date at which the migration is thought to have taken place.
As for the paper, itself, is to say the least rather technical and has nothing whatsoever to say directly on the subject of the ‘Out of Africa’ hypothesis. Rather, as indicated by its final paragraph, it raises some interesting questions as to possible origins of the recent discovered Homo floresiensis, the entire misnamed ‘Hobbit’, while suggesting that the actual residents of the newly re-dated sites might have more closely related either to Homo heidelbergensis or to the Bodo cranium, which dates to 600,000 years old and which is thought to fall somewhere between Homo erectus and Homo heidelbergensis.
If the middle Pleistocene 40Ar/39Ar ages better reflect the age of the Solo River 20 meter terrace deposits and hominins, the site of Ngandong remains a relatively late source of H. erectus; however, these H. erectus would not be the contemporaries of Neandertals and modern humans, and their chronology would widen the gap between the last surviving H. erectus and the population from Flores – whose source population has been argued to be Indonesian H. erectus; although this point is contested. Instead, the Ngandong hominins would be contemporaries of the H. heidelbergensis from Atapuerca, Spain and elsewhere in Europe, and, possibly the archaic H. sapiens specimen from Bodo (Ethiopia), which might favor arguments that they are more closely affiliated with these taxa and differ from H. erectus. Such ages for Ngandong would suggest that a series of geographically relatively isolated lineages of hominins lived during the middle Pleistocene.
For once, it has to be said that the Daily Mail cannot be blamed for reaching an erroneous conclusion. While finishing up this article, I decided to take a qucik look around, using google, to see if I could track the original source of the story and very quickly hit paydirt via Eurekaalert, which shows that that it comes from a press release issued by James Devitt, Deputy Director for Media Relations at New York University.
The press release includes the spurious claim that:
The existence of the two species simultaneously has important implications for models about the origins of modern humans. One of the models, the Out of Africa or replacement model, predicts such overlap. However, another, the multiregional model, which posits that modern humans originated as a result of genetic contributions from hominin populations all around the Old World (Africa, Asia, Europe), does not. The late survival of Homo erectus in Indonesia has been used as one line of support for the Out of Africa model.
However, findings by the SoRT Project show that Homo erectus’ time in the region ended before modern humans arrived there. The analyses suggest that Homo erectus was gone by at least 143,000 years ago—and likely by more than 550,000 years ago. This means the demise of Homo erectus occurred long before the arrival of Homo sapiens.
As already noted, the ‘Out of Africa’ hypothesis predicts such an overlap if, and only if, a hominid species existed at the same time as the Homo sapiens migration and, as such, the new dating evidence does nothing more than remove an erroneous piece of evidence that was incorporated, post-hoc, into the hypothesis on the basis that the previous, and incorrect, dating of the Indonesia sites predates the formulation of the hypothesis. The loss of Homo erectus from this picture has no effect whatsoever on the evidence from the Neanderthals not does it rule out the possibility, if not likelihood, that we are missing a hominid species or two (or even more) from our picture of human history as it relates to the continent of Asia which, after all, is a pretty big place to be looking for a few fragments of bone and, hopefully, some stone tools.
The claim here may be technically correct but it doesn’t merit the suggestion that the ‘Out of Africa’ hypothesis has been called into doubt by this one paper – that claim has all the appearance of being no more than a piece of contrived puffery which has been put forward solely for the purpose of screwing a few column inches out of the kind of journalist whose understanding of evolution comes from watching Pokemon cartoons.
What makes this all the more galling is the fact that one of the leading, if not the leading, 19th century proponents of the African origin hypothesis was the great Charles Darwin – and that fact alone may be enough to ensure that a paper that is otherwise a useful contribution to the onerous task of tidying up the evidence of human evolution is likely to be recycled by creationist fucknuts into yet another utterly false ‘Darwin was wrong’ meme.
For that reason, and for its appalling misrepresentation of the findings of this paper, the NYU press office should be thoroughly ashamed of itself.