IT WAS the evolutionary find of the century: a diminutive human-like fossil that called into question basic assumptions about the origin of our species. No, not Homo floresiensis, aka the hobbit, discovered in Indonesia a decade ago this September. This troublemaker, an equally tiny member of the human lineage 鈥� the hominins 鈥� was unearthed some 80 years earlier. The discovery in 1924 of the Taung child astonished and unsettled researchers because it didn鈥檛 fit their picture of human evolution. It came from a continent few thought was key for human evolution: Africa.
No one now doubts that Africa was the cradle of humanity 鈥� the idea goes back to Darwin after all 鈥� but early in the 20th century most researchers believed we evolved in Eurasia. The Taung child was the first fossil to challenge that orthodoxy. And Raymond Dart, an anthropologist at the University of Witwatersrand in Johannesburg, South Africa, earned himself an academic mauling for placing his discovery in a brand new hominin category he named Australopithecus (鈥渟outhern ape鈥�). It would take his critics several decades to admit they were wrong.
But could they have been right about Eurasia after all? Recently, some prominent researchers have come round to the idea that hominins may have left their African cradle much earlier than we thought and undergone critical evolutionary transitions further north. There are even whispers that one of the most important evolutionary events of all 鈥� the appearance of our genus, Homo 鈥� may have occurred under Eurasian rather than African skies. And the catalyst behind this radical rethink? That pesky little hobbit.
Advertisement
From the beginning, the hobbit, like the Taung child, did not fit the standard picture of human evolution (). Some of the remains found on the Indonesian island of Flores were just 18,000 years old. So the hobbit was alive at least 10,000 years after every other hominin except our own species had become extinct. The one relatively complete skeleton belonged to an individual who was barely 1 metre tall. Bone fragments suggested other hobbits were even shorter. Then there was the skull. The cranial volume of the single hobbit skull found so far is around 420 cubic centimetres, about one-third the size of a modern human鈥檚. Yet stone tools found with hobbit bones suggested that the hominin was capable of sophisticated behaviour. 鈥淚t drove me nuts in 2003,鈥� says Peter Brown at the University of New England in Armidale, Australia, who led the team that made the discovery. 鈥淲hat do you compare a unique small-bodied, small-brained hominin dated to only 18,000 years with?鈥�
Some felt the answer was obvious. Some modern humans are born with unusual diseases that arrest growth of the cranium. The hobbit skull could have belonged to one such individual and, in fact, be human (New 杏吧原创, 14 October 2006, p 17).
Robert Martin at the Field Museum in Chicago is a proponent of this idea. He points out that hominin brains have gradually got bigger throughout our lineage鈥檚 evolutionary history. If the 18,000-year-old hobbit was really a product of human evolution, it should have had a skull roughly the same size as ours, he says. Instead it is similar to one of Dart鈥檚 australopiths, which went extinct about 1.2 million years ago. The body size is also unusual, he adds, but then again some human populations today are small. 鈥淭he most likely explanation for that small brain is a pathology 鈥� especially considering we only have the skull from one individual,鈥� says Martin. Unusual asymmetries in the hobbit skull also suggest that there was something unhealthy about this individual, according to two more supporters of the idea, Robert Eckhardt at Pennsylvania State University in University Park and Maciej Henneberg at the University of Adelaide, Australia.
For Dean Falk at Florida State University in Tallahassee, this kind of scepticism is no more than a repeat of the reception that greeted Dart in the 1920s. Having studied scans of the hobbit skull to work out the shape of its brain, she concludes that H. floresiensis is indeed a new species because of its tiny skull 鈥� not in spite of it (). Any unusual asymmetry is simply down to crushing during burial. But she accepts that this interpretation attracts criticism because it threatens the orthodoxy. 鈥淭he moment the first Homo floresiensis paper was published there was a vociferous group of scientists screaming 鈥榥o, no, no鈥�,鈥� she says. 鈥淚t was the same old story as Taung 鈥� things haven鈥檛 changed.鈥�
Falk鈥檚 work suggests H. floresiensis is closely related to a larger extinct hominin called Homo erectus, which we know lived in Indonesia between about 1.7 million and 550,000 years ago. With evidence of 840,000-year-old stone tools on Flores, it is possible that a population of H. erectus arrived on the island around that time and became isolated there. Animals often shrink when isolated on islands, so that may partly explain the hobbit鈥檚 small size.
It is another point on which Martin begs to differ. 鈥淭here is simply no good precedent for island dwarfism affecting brain size in any primate,鈥� he says. The debate continues to rage. 鈥淚t鈥檚 very acrimonious,鈥� says Falk.
Meanwhile, Brown and others have shifted their attention below the hobbit鈥檚 neck. There may be only one skull, but there is a veritable treasure trove of bones belonging to at least four hobbits. These show a consistent pattern of features, and together they indicate that hobbits had shoulders, wrists, limb proportions and feet that are, if anything, even more bizarre than the contentious skull (). 鈥淭here were just so many primitive features that the hobbit team began to talk seriously about Homo floresiensis being derived from something more primitive than Homo erectus,鈥� says William Jungers at Stony Brook University in New York, who led some of the analyses. According to Brown, somewhere towards the very top of the list of the hobbit鈥檚 likely recent ancestors is one of Dart鈥檚 australopiths.
This idea borders on the incendiary. It is one thing to declare the hobbit a valid species and break the cardinal rule that hominin brains get bigger over time. But to go further and suggest the tiny hominin evolved directly from an australopith threatens the decades-old central narrative of the human evolutionary story.
鈥淭he idea that the 鈥榟obbit鈥� evolved directly from an australopith threatens the central narrative of human evolution鈥�
鈥淲e鈥檙e taught that Australopithecus only ever lived in Africa 鈥� that鈥檚 textbook,鈥� says Falk. Conventional wisdom suggests the australopiths evolved in Africa about 4 million years ago and died out there 2.8 million years later. Perhaps it was their short legs that discouraged them from making the long trek out of Africa. Certainly it wasn鈥檛 until the taller members of our own genus appeared, right towards the end of the australopith age, that hominins began to explore the wider world.
Out of Africa, then back again?
The hobbit remains hint at an alternative. Perhaps an australopith did manage to escape Africa before the Homo genus evolved, and perhaps it survived long enough in Eurasia to evolve into the hobbit.
If so, shouldn鈥檛 we have found some fossil evidence for these ancient Eurasian australopiths by now? Not necessarily, says Brown. Environmental conditions in East and South Africa favoured preservation of human fossils in a way that conditions across Asia did not, he says. For Martin, however, the very idea of Eurasian australopiths is untenable. 鈥淚 can鈥檛 understand my colleagues,鈥� he says. 鈥淭hey are incredibly careful to stamp all over suggestions of anything remotely out of the ordinary in human evolutionary thought, and yet some of them swallow this notion completely. There鈥檚 not a scrap of fossil evidence to support this idea.鈥�
That鈥檚 not entirely true, though. There is one site in Eurasia that could fit with the idea that australopith-like hominins made it out of Africa. What鈥檚 more, there are hints that these enigmatic Eurasian australopiths did more than evolve into the hobbits found on Flores: they may have given rise to our own genus.
In 1991, researchers excavating the medieval town of Dmanisi, Georgia, in the Caucasus came across the earliest hominin remains found outside Africa so far. There is still some debate over exactly where the 1.77-million-year-old Dmanisi hominins fit in the human evolutionary tree, but most would classify them as H. erectus. Their age and primitive features suggest they were among the earliest members of this species, implying that H. erectus wasted little time in leaving the East African region in which it first appeared perhaps 1.87 million years ago. Conventional thinking has it that this was the first time a hominin ventured out of Africa, with Dmanisi offering a unique snapshot into the very moment that humans went global.
Then, in 2011, came surprising news from Dmanisi that challenged this picture. Continued excavations had found evidence that the Georgian site was first occupied at least 1.85 million years ago 鈥� essentially at the same time that H. erectus appeared in East Africa. This led David Lordkipanidze of the Georgian National Museum in Tbilisi and his colleagues to consider an extraordinary alternative human history. H. erectus could have evolved in Eurasia, they say. If so, the fossils at Dmanisi are not a snapshot of the first hominin migration north out of Africa, but rather catch H. erectus in the act of migrating south into the land of its forefathers (). 鈥淚t has to be a feasible idea,鈥� says Lordkipanidze.
More broadly, the new dates of occupation at Dmanisi mean that H. erectus could have evolved from an australopith that left Africa around or before the 2-million-year mark. Falk says her work on the hobbit skull is consistent with this view. The similarities she identified between its brain shape and that of H. erectus could be explained if both arose from a common ancestor in Eurasia, rather than the hobbit being descended from H. erectus.
While the Dmanisi fossils add extra spice to the hobbit story, when it comes to understanding our own evolution it鈥檚 the H. erectus story that really matters. 鈥淚 think Homo erectus is the first hominin for which you can make a case that it belongs to our genus, Homo, without having to explain away any important exceptions,鈥� says Bernard Wood at George Washington University in Washington DC. A more primitive species, Homo habilis, often placed in our genus, may not belong there or be a direct ancestor, he adds (). Crucially, H. erectus is often seen as the direct ancestor of our species. So if it evolved in Eurasia before moving into Africa where our species evolved about 200,000 years ago, modern humanity is arguably the product of both an African and a Eurasian cradle (see diagram).
Wood stresses that the evidence from Flores and Dmanisi is compatible with these radical new ideas rather than strongly supporting them. The fossil evidence from Eurasia is still meagre. That won鈥檛 change until researchers accept the possibility that australopiths made it into Eurasia and birthed our genus there, and start looking for evidence. 鈥淯nless we open our minds to the possibility that some of that innovation happened outside Africa, we鈥檒l never find it,鈥� he says.
However, the African fossil record is also surprisingly silent on the origin of H. erectus. 鈥淭here鈥檚 a difficult gap between 2 and 3 million years ago in East Africa where the material is incredibly fragmentary,鈥� says Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. During this time interval, when H. erectus was evolving, 鈥渢here is nothing that screams erectus鈥� in the African fossil record. It鈥檚 an absence that certainly could be explained if this pivotal species evolved outside the continent, he says.
Nevertheless, Spoor is not convinced this is what happened. 鈥淚t鈥檚 an interesting exercise to think of an early pre-Homo erectus migration out of Africa, but there鈥檚 really no hard evidence in the form of fossils or stone tools to support it,鈥� he says. He studies hominin skulls, and still thinks the hobbit is best seen as a dwarfed species that evolved from something like H. erectus, not one that descended from a common ancestor of them both. 鈥淥thers have called this kind of thing 鈥�X-Files palaeontology鈥�. It does smell a little like that.鈥�
鈥淥thers have called this kind of thing 鈥榅-Files palaeontology鈥�. It does smell a bit like that鈥�
Despite the considerable problems with the African fossil record, Wood thinks that it will be tough to get researchers to take Eurasian alternatives seriously 鈥� perhaps, ironically, because Dart and his successors did such a good job of building up the African story. 鈥淭he struggle to get people to talk about Eurasia wouldn鈥檛 necessarily be as hard as Dart found it to get people thinking about Africa in the first place, but it would certainly be a similar kind of fight,鈥� says Wood.
Eckhardt, Henneberg and Martin take a different view. They think that Wood underestimates the power of a seductive new twist in the tale of human evolution, even with a lack of supporting fossil evidence. They suggest that the true modern-day Darts are not those struggling to get people thinking about the Eurasian australopith idea, but those fighting to oppose it.
What both sides can agree on is that there will be important academic clashes in the years ahead as new fossils come to light that either support or refute the ideas that were let loose when the hobbit was unearthed. With those tussles looming on the horizon, it is not surprising that Raymond Dart鈥檚 name is mentioned so frequently 鈥� after all, he triumphed in the end.
鈥淚t took Dart 30 years to be vindicated,鈥� says Eckhardt. 鈥淲e鈥檙e only coming up on year 10 since the finds on Flores.鈥� Keep watching to find out which way the fossil evidence falls.
This article appeared in print under the headline 鈥淥ur Asian origins鈥�
