Tuesday, April 28, 2009

Howdy, cousin!

The New York Times is running an article on the current status of the Hobbit people. But not Frodo or his kin. No, these are the ones which have stirred so much controversy and speculation in the world of paleoanthropology. These are Homo floresiensis, the Little People of Flores.

Six years ago, scientists digging in a cave on the tiny island of Flores in Indonesia discovered the not-quite-fossil remains of a creature that was not-quite-human-as-we-understand-it. Bones from a total of nine individuals were uncovered and are now the subject of curiosity, examination, skepticism, and profound wonder.

They look human, or at least, they look like primates. They had opposable thumbs, forward facing eyes, and cheekbones. They stood upright. They walked on two legs. They weren't monkeys. They weren't apes. They might have been human, or they might not have been.

By human, I mean the species Homo sapien. To the best of our knowledge and the fossil record, modern humans showed up in Africa around 150,000 to 250,000 years ago. From there, beginning around 75,000 years ago, we left Africa and slowly but surely colonized the rest of the world. We reached Australia 50,000 years ago, and the earliest evidence we have for modern humans in Indonesia is around 40,000 years old.

So, are the Little People of Flores human, or are they another hominid species? We may be alone now, but the world used to be filled with our sibling and cousin species.

Here's what we know:

In the Liang Bua cave on the island of Flores in Indonesia, an archeological expedition discovered the remains of nine different individuals. The oldest of these remains was 94,000 years old. The youngest was 17,000 years old. There is no one, complete skeleton. There is only one complete skull and one other lower jawbone. The rest of the remains are a collection of very incomplete bones, but these very incomplete bones have some very startling anomalies.

First, at their best determination, the anthropologists concluded that the individuals they found averaged three and a half feet in height. The one skull had a brain case that would have held a brain only one-third the size of a normal modern human's. Neither the complete skull nor the intact lower jaw had evidence of a chin. Even the most inbred of aristocrats can still lay claim to a chin, however receding it might be.

The upper arm bone was closer in its shape to an ape than it was to a human. The same is true of the wristbones, the collarbone, and the shoulder blade. The foot bones lacked the structure necessary to form an arch, meaning the feet would have been completely flat. Finally, the premolar has non-human features, like a double root.

What can explain this? Sure, we could say they were a completely unknown species of hominid, but that's an extraordinary claim in need of extraordinary proof. This is where the controversy comes in.

Begin with the most conservative possibility. The remains belong to modern humans, and there are reasonable explanations for each of the strange anomalies found in their anatomy. The most noticeable difference is their height.

Three and a half feet is, in human terms, tiny. It's how tall a four year old girl might be. It's shorter than someone with achondroplasia, the most common form of dwarfism in humans. It's shorter than the average height of the African Pygmies, who stand about four feet ten inches tall. While there are adult humans shorter than that – the shortest person on Earth is He Pingping of Monglia, and he's two and a half feet tall – their lack of height is considered a disability.

Could they have been children? Before puberty, the ends of the long bones have a section, a plate, of cartilage, which is tough and flexible. This allows the bones to grow in length during childhood. When a person reaches the end of puberty, these plates become bone, and the growth of the long bones stops. In all the recovered bones, the growth plates were bone, not cartilage. These were not children.

Could they have been dwarfs? There are many causes of dwarfism – some genetic and some environmental. Each type of dwarfism comes with certain features. For instance, achondroplastic dwarfs have normal-sized torsos and short limbs. They also have handsome facial features and skulls slightly larger than normal.

However, there is no currently known form of dwarfism that includes all the different features found in the remains of the Little People of Flores. Perhaps it could be a completely unknown form of dwarfism, but that is another extraordinary claim, and it will require its own extraordinary evidence. Set it aside for now.

Perhaps these are modern humans who became small through a process known as insular dwarfing. Insular dwarfing takes place when a mammalian species finds itself isolated on an island. With a finite amount of space, food, water, and other resources, the pressures of selection favor smaller individuals. The individuals who survive to have children are themselves smaller than the last generation. Over the course of many generations, the population becomes significantly smaller.

My favorite example of this is the pygmy mammoth. While there are no more mammoths at all anymore, we know that when they did exist, they mostly stood about 14 feet tall and weighed around 20,000 pounds. But, on the Channel Islands off the coast of California, there was a subspecies of mammoth that was only four-and-a-half to seven feet tall and weighed, at most, 2,000 pounds. Surely this could have happened to humans.

It has. There are human populations in the world – the African Pygmies, the Maylasian Semang, and Bengali Andamanese – which are much smaller in stature than average, but even they stand about four and a half feet tall. The Little People of Flores are a foot shorter.

Another indication that Homo floresiensis was not subject to insular dwarfism is their brain size. In the known cases of insular dwarfism, the size of the brain was not affected. Homo floresiensis had a far smaller brain than modern humans.

So, they are not children. They are not individual;y dwarfs, and they are not a subspecies of insular dwarf humans. What about their brains?

That leads us to our next argument. Perhaps the individuals found in Luang Bua were people with very small brains – a medical condition called microcephaly. There are features of microcephaly that simply do not appear in the one intact skull. Further more, microcephaly is a very rare condition, showing up in less than one person in ten thousand. Fossil remains are rare enough. Only about one creature in a million has the luck to be fossilized after death. The possibility of a fossil skull being an example of a rare disorder like microcephaly is astronomical.

So, if it's not microcephaly, what is it? One-third the size of modern humans sounds pitiful in comparison, and it is, if you're talking about human cognition. But that one-third is actually about the same size as a chimpanzee's brain, and no one ever said chimpanzees didn't have it on the ball. A human with one-third the average brain wouldn't survive a week. A chimpanzee does just fine.

That brain size is also comparable to Homo habilis, the Tool-Making Man, a distant ancestor of Homo sapien.

There is no absolute here. There are very few bones of the same kind that survived from multiple individuals. We could be looking at some very aberrant humans. However, the likelihood of each of these individuals spread over 77,000 years each possessing some rare mutation beggars the imagination. It's far more reasonable to assume that all nine shared a set of characteristics which set them apart from Homo sapiens.

What does this tell us? I believe it tells us that our family tree is far more varied than we expected, and that stranger things await us still. I believe, from the evidence at hand, that the remains found in Liang Bua represent a previously unknown hominid species, one that survived almost until historic times. This species, it appears, emerged from the hominid line sometime after Homo habilis and possibly before or concurrent with Homo erectus. It may indeed be an insular dwarf species, but one that is not human. It may even be the source of local folk tales regarding the Ebu Gogo, small hairy people who lived in the jungle of the island and avoided human beings

What a wonderful damn world this is.