Saturday 30 November 2013

The Small Problem of the Hobbit

Homo floresiensis (cast)

I'm obviously not keeping up.

Reading Becoming Human: Our Past, Present and Future a special publication by Scientific American editors, the chapter Rethinking the Hobbits of Indonesia by Kate Wong was something of a surprise.

I had assumed the so-called 'Hobbit', the diminutive hominid known to taxonomists as Homo floresiensis and to paleoanthropologists as LB1, after Liang Bua, the name of the cave it was found in in 2004 on the Indonesian island of Flores, was generally considered just that - a member of the Homo genus which had become miniaturised. Miniaturisation is common on islands, probably in response to limited resource and a generally smaller number of predators.

The problem, as I understood it, was that the cranial capacity of LB1 was only a little larger than a chimpanzee's and yet stone tools were found associated with it which showed a tool-making ability at least as advanced as H. erectus with a far larger brain. Now, whilst brain size is not absolutely correlated with intelligence, there is a noticeable increase in design and function of tools as brain size increased over human evolutionary history, so the apparent H. erectus level of tool making skill with a chimpanzee-sized brain was hard to explain.

To overcome this some researchers had proposed that, rather than a different species evolved to suit an island environment, LB1 may have been an H. erectus, or even a population of them, suffering from a medical syndrome such as:
  • Laron syndrome, a genetic disease that causes insensitivity to growth hormone.
  • Myxoedematous endemic cretinism, a condition that arises from prenatal nutritional deficiencies that hinder the thyroid.
  • Microcephalic osteodysplastic primordial dwarfism type II, a genetic disorder whose victims have small bodies and small brains but nearly normal intelligence.

Given how little we know about the Asian hominin record, there is plenty of room for surprises. What we need, of course, are more discoveries — from Flores, neighboring islands such as Sulawesi, mainland Southeast Asia or anywhere else in Asia

Robin W. Dennell; University of Sheffield, England.
But now it seems LB1 may not even be a member of the Homo genus at all, let alone a diminutive H. erectus, and whilst that explanation might answer some of the questions a different hominin surviving on a small island until possibly as recently as 12,000 years ago raises, it raises a whole lot of different ones and means we may have to revise some of our basic assumptions.

A detailed analysis by William L. Jungers of Stony Brook University has shown that LB1 had more in common with Australopithecus afarensis ("Lucy") from East Africa, and some features are even more primitive. The length of it's foot was 70 percent as long as the thighbone, the big toe was short and the fool lacked an arch. These features are closer to those of the bonobo than any known hominin or australopithecine. Although LB1 was undoubtedly bipedal, as were the australopithecines, some of the bones of the wrist and shoulder girdle are more ape-like and the pelvis is australopithecine, and yet some of the facial bones are distinctly hominin.

In this respect, LB1 is similar to early H. habilis - assumed to be the ancestor of H. erectus - in having a mixture of primitive ape-like characteristics mixed with some hominin features.

This has led some paleoanthropologists, such as Dr. Debbie Argue of the Australian National University in Canberra, to propose that LB1 branched of the hominid evolutionary tree either:
  • Between H. rudolfensis and H. habilis between 2.3 and 2 million years ago.
  • Between H. habilis and H. erectus between 2 and 1.8 million years ago.
All three of these evolved in East Africa almost certainly from an Australopithecine such as A. afarensis or A. sediba.

An analysis of the stone tools also supports this idea as they as more like the stone tools made probably by H. habilis between 1.2-1.9 million years ago, in Olduvai Gorge in Tanzania than those of later humans.

These would appear to fit with the known anatomy of LB1 but, as I said earlier, it raises a whole lot of new questions because it requires a primitive hominin to have migrated out of Africa, across Asia, or maybe round the coast, far earlier than we thought and, one assumes, with less intellect with which to adapt to the different environments on the way, and apparently without trace. Of course, that latter might be because we just haven't found any yet.

But the assumption that humans needed to evolve large brains, advanced technology and maybe even long strides before they could migrate out of Africa may not be a valid one. Indeed, if it turns out that a small early human or even an australopithecine with a chimpanzee-sized brain made it all the way to a small island in Indonesia some 2 million years ago, that assumption is false.

Biologically, provided there was a more or less contiguous environment similar to that found back home, there is no reason at all why any species shouldn't spread out of its home continent, and it may well be that, for a brief period, grasslands similar to those thought to have existed in East and South Africa at that time extended across the Middle East at least to India and probably beyond, hence the incidence of related species like rhinoceroses, elephants, big cats, etc, in Africa and Asia.

Today the oldest unequivocal evidence of humans outside of Africa comes from the Republic of Georgia, where researchers have recovered H. erectus remains dating to 1.78 million years ago. The discovery of the Georgian remains dispelled that notion of a brawny trailblazer with a tricked-out toolkit because they were on the small side for H. erectus, and they made Oldowan tools, rather than the advanced, so-called Acheulean implements experts expected the first pioneers to make. Nevertheless, they were H. erectus.

But if proponents of the new view of hobbits are right, the first intercontinental migrations were undertaken hundreds of thousands of years earlier than that— and by a fundamentally different kind of human, one that arguably had more in common with primitive little Lucy than the colonizer paleoanthropologists had envisioned. This scenario implies that scientists might locate a long-lost chapter of human prehistory in the form of a two-million-year record of this pioneer stretching between Africa and Southeast Asia if they look in the right places.

Scientific American Editors (2013-09-23). Becoming Human: Our Past, Present and Future
(Kindle Locations 2137-2145). Scientific American. Kindle Edition.

Clearly there is still a great deal to learn about the human story. The problem is in keeping up with all the new research.

Thank you for sharing!

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1 comment :

  1. On the hobbit: I think one thing scientist may be missing is that chimps and orangutans aren't just relics left over from a population that was going to become human. In the early days, and even to some extent now, they were competitors with humans, at least at the margins. Chimps are better at a set of things than humans are, and humans are better at a different set of things than chimps are. In the absence of humans, chimps would probably colonize savannas and eat meat to a greater extent than they currently do because the niche would be open to them and humans wouldn't be there to kill them. As a matter of fact, I believe I recall reading that when they're protected on reserves, chimps do colonize savannas, become more frequent tool users, etc.

    Basically, when both humans and great apes are present, they subdivide a niche, with each specializing in a portion of it. When you think about it that way, chimps are less human-like because the part of the niche that being human-like would help them fill is already occupied. The other half of that subdivision is that there is a part of the niche that humans can't use as effectively as chimps. Humans are less chimp-like than they might otherwise be, because chimps already occupy the niche that being more chimp-like would help humans fill.

    Now, put a primitive human, probably something at about the level of the Georgian Homo erectus, on an island with no great apes. The part of the great ape/human niche that humans occupied is open, but so is the part that is occupied by chimps or orangutans on the mainland. I would be surprised if the primitive humans didn't develop/redevelop some apelike characteristics. Open ecological niches get filled if there is something out there to fill it, and primitive humans would not be far from being able to fill that niche. Primitive humans colonizing the part of the ape/human niche that apes normally hold would lead to a confusing mosaic of human traits (read as advanced traits) and ape-like traits (read as primitive).

    All that seems reasonable to me. Anybody see problems with it?


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