Saturday, May 27, 2006

Hunting Hobbits

In a hole in the ground there lived a hobbit. ~ J. R. R. Tolkien

Homo floresiensis, also known as “the hobbit”, has become a contentious issue as some scientists are arguing that the fossil hominid is a diseased Homo erectus, not a dwarf version.

It's hardly surprising that such an interesting group of bones would cause controversy. Just about any new hominid find gets the anthropologists into an uproar. For example, Donald Johanssen, discoverer of Lucy, and Richard Leakey were on opposite sides when it came to the discussion of the human family tree. Leakey felt a skull he had found was an earlier human ancestor than Johanssen's Lucy. When that key fossil in the Leakey case was found to have been incorrectly dated, the debate cooled for a while, but that didn't change Leakey's mind much, and a team led by his wife, Maeve, more recently discovered a fossil that raised most of the questions all over again.

It's easy to understand why there is so much debate. We have literally tons of dinosaur remains; we have mammoths coming out of our ears; the La Brea tar pits have enough bones of sabre-tooth cats and other animals to fill a bunch of zoos were they suddenly to come to life. But when it comes to human ancestors, the record is considerably more sketchy. This is relatively easy to understand. For one thing, there weren't near as many hominids and early humans running around as there were woolly mammoths. Second, early hominids were often dinner for various predators, which meant the bones were getting crunched up and scattered about. There was far less liklihood of a hominid's or an early Homo's bones to be thoughtfully laid out in a stream bed for some enterprising graduate student to dig up a few hundred thousand years later.

As a result, anthropologists tend to do a lot of theorizing based on the discovery of a few teeth or a skull cap. When they find a significant portion of a skeleton, well, they tend to go a little nuts. According to some scientists, this is what has happened to Peter Brown and Mike Norwood, discoverers of Homo floresiensis. Brown and Norwood, as noted, theorize that the so-called “hobbit” is a down-sized version of Homo erectus. He got small because his ancestors ended up stranded on an island, so they got smaller to adapt to the limited food supply and space.

There is good evidence for this sort of thing occurring in the animal world. Pygmy mammoths have been found in places that were cut off by water from the mainland after regular-sized mammoths arrived. Pygmy dinosaurs have been discovered in similar sorts of areas in Romania. It's natural to expect natural selection to operate in favor of downsizing animals when food and space is at a premium. And, of course, pygmy humans exist today, although for different reasons, but their existence shows that human groups can come in all sizes. Some experts, however, are casting doubts on whether “the hobbit” is, in fact, a miniaturized erectus.

The debate is about the size of floresiensis' brain. Even allowing for dwarfism, the brain appears to be too small. According to a team led by Robert Martin, the skull found in Indonesia is actually microcephalic, a known medical condition that causes an abnormally small brain. The discoverers, of course, hotly debate this, pointing out that they have found other small bones and tools. Surely they couldn't have found an entire tribe of microcephalics. If, by some extraordinary chance they had, such a group would be incapable of making the tools the excavators found.

The problem is that, while more bones have been found, there's only one skull, and based on the size of its brain relative to the predicted size of a dwarfed human, it would be microcephalic. What is needed, then, are more skulls or, at least, parts of skulls of sufficient completeness to determine the size of the brain.

Easy for me to say. Hominid skulls are scarcer than hen's teeth anyway, as I've said. In a small population (numbers, not stature) they'll be even harder to find.

It will be interesting to see what, if any, further discoveries are found in Indonesia. The case on Homo floresiensis is not closed and may turn out to be a fascinating look at evolution at work. There is still work that can be done investigating the indigenous population of the area to see if a connection can be found from the small-statured (but not abnormally so) local inhabitants and their possible tiny ancestors.

But I do hope that they stop calling the little devil “the hobbit.” I keep expecting them to find elves next.

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