Island of the Lost Hominids

LB1 and modern human.jpgGet to know that little skull. Scientists are going to be talking about it for centuries.

As researchers report in tomorrow's issue of Nature, the skull--and along with other parts of a skeleton--turned up in a cave on the Indonesian island of Flores. Several different dating methods gave the same result: the fossil is about 18,000 years old. (Additional bones from the same cave date back to about 38,000 years.) If all you had was the 18,000 year figure and this picture to go on, you might assume that the skull belonged to a small human child. After all, there is plenty of evidence that Homo sapiens had already been in this part of the world for 25, 000 years. But you'd be wrong.

The skull actually belongs to a previously unknown species of hominid, whose ancestors split off from our own some 2 million years ago. Homo floresiensis, as it's known, stood three feet high as an adult and had a brain less than a third the size of our own.

To understand just how mind-blowing Homo floresiensis is, you have to consider it in the context of hominid evolution. Our closest living relatives (chimpanzees and bonobos) live in Africa, and both genetic and fossil evidence indicate that the common ancestor we share with them lived in Africa as well. The oldest known hominids--those species more closely related to us than chimps or other primates--date back 6 million years. They were short, probably could walk upright, and had brains about the size of a chimpanzee--about 350 cubic centimeters. It was only about 2.6 million years ago that hominids started using stone tools, and only about 2 million years ago that species emerged that stood as tall as we do. Its brain was also bigger--850 cc. The increase in brain size may not have been all that significant, since bigger mammals tend to have bigger brains, smart or not. But shortly after this evolutionary surge, the first hominids turned up outside Africa. Homo erectus moved as far east as China and Indonesia within just a few hundred thousand years. At the very least, their migration suggests an expanding population of meat-eaters who have to seek out much bigger ranges than their ancestors.

The Asian population of Homo erectus had little, if anything, to do with our own origins. The oldest human fossils, dating back 160,000 years ago, were found in Africa, and there's a pretty good chain of evidence showing that Homo sapiens descends from hominids who stayed home on the mother continent while Homo erectus swept across Asia. For instance, African hominids underwent a massive burst of brain expansion around 500,000 years ago to close to our own capacity. Meanwhile, Homo erectus in Asia underwent a slight increase, if any. Humans only expanded successfully out of Africa about 50,000 years ago. They may have interbred with Homo erectus, but most of our genome still points back to a recent African origin.

Paleoanthropologists were first attracted to Flores when 800,000 year old tools were found on the island in 1998. Boats seem to have been essential for getting to Flores, which speaks of a pretty impressive mental capacity for Homo erectus . (On the other hand, lizards and elephants and other land animals got to the island without a boat--perhaps by swimming being swept away on logs during storms.) Researchers poked around on Flores, and last September they turned up something none of them had expected: Homo floresiensis. Homo floresiensis was not an ape--it had the signature traits of a homind, such as a bipedal anatomy and small canine teeth. But it wasn't a pygmy human, either. Pygmy brains are in the normal range of variation for our own species. What's more, the floresiensis brain wasn't just small but had a drastically different shape than ours--a shape more like the brain of Homo erectus. This and other anatomical details have led the researchers to conclude that Homo floresiensis branched off from Homo erectus and evolved into a dwarf form.

Here is case-closed proof that today's solitary existence of Homo sapiens is a fluke in the history of hominids. Even 18,000 years ago, at least one other species walked the Earth with us. Exactly how Homo floresiensis went extinct no one knows, but close to the top of the list would have to be ourselves. Neanderthals survived only a few thousand years after humans turned up in Europe, and Homo erectus seems to have disappeared from Indonesia around 40,000 years ago, just around the time humans came on the scene. Perhaps Homo floresiensis lasted longer on Flores because it was harder for humans to reach.

A dwarf hominid on an island is fascinating for another reason--islands are famous for fostering the evolution of dwarf animals, from deer to mammoths. It's possible that the small territory of islands and the lack of competition and predators favors the small. For the first time, hominids have fallen under the same rule. Islands mammals have also been shown to sometimes evolve much smaller brains, and, incredibly, the hominid brain is subject to the same rule. Homo floresiensis's brain shrank down to the smallest size ever found in a hominid. Did Homo floresiensis lose the mental capacity to use tools along the way? The researchers found stone tools in the same site where they found Homo floresiensis, but it's not clear whether Homo floresiensis made the tools, or humans used them (perhaps to kill Homo floresiensis?).

One of the most interesting questions that comes to mind with the discovery of Homo floresiensis is how far back it goes in the fossil record. Just how long did it take for a lineage of hominids to lose half their height and two-thirds of their brain? It may have taken a million years, or a few hundred thousand, or maybe less. In a commentary in Nature, Marta Lahr and Robert Foley of Cambridge point out that it only took 12-foot high elephants on Malta only 5,000 years to shrink to the size of a dog. I've always been a bit skeptical when people forecast dramatic change for our species. But if evolution can produce Homo floresiensis, who knows what a few thousand years on Mars or another solar system could take our descendants?

Update, 11/1/04: Here's a bundle of papers, interviews, and such on H. floresiensis from Nature. Much of it is free.

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Anything--anything--is possible.

By William Gruzenski (not verified) on 27 Oct 2004 #permalink

How long would it take to produce a dwarf Rotweiler that bred true? In dog years?
Is there an assumption that any fossil is representative? So that what may have been a freak driven off to the margin is assumed to be right out of the heart of the species?

By vernaculo (not verified) on 27 Oct 2004 #permalink

Thanks PZ. That makes the next question for me, as curious dilettante - how many other bands, or tribes of cousins have there been? Boy howdy.
"(perhaps to kill Homo floresiensis?)" seeming a likely interpretation, if not here certainly for the Neanderthal, and how many others?
So are we different now? Or just enjoying the peaceful aftermath of our violent successes?
Do the Bushmen of the Kalahari have the right to that moral regard?
How dispassionately can science view that extermination?

By vernaculo (not verified) on 27 Oct 2004 #permalink

Great post, Carl. Re your last paragraph, for an example a bit closer to home, I recall reading (probably in Science News) some years ago that present-day domesticated cats have brains only half the size of their wild ancestors, ca 20,000 years BP. In my more cynical moments, I wonder how much stupider people have gotten since the invention of agriculture ...

Thanks for an informative post. I was directed here by a commenter at Crooked Timber, and I suspected that this was an important breakthrough but didn't know exactly why. You've done a great job of clarifying the scientific stakes in this discovery, and I look forward to reading more of your work in the future.

By Jackmormon (not verified) on 27 Oct 2004 #permalink

I'm a little confused about their brain size. If they lost half their height, and their brain shrunk proportionally, it would be an eighth of the original size. Since they were actually a third of the previous size, weren't their brains larger than expected? Or do brains not scale like this?

This discovery is truly fascinating. Logic would lead one to believe that it shows Homo erectus survived even longer than we have thought. Which leads me to think that it might be presumptuous to name this a different species. Although I believe I read that no genetic material had been isolated yet, I assume that it eventually will be. Comparison of mitochondrial DNA with Homo erectus should provide some interesting information.

Since this homonid evolved before the end of the last ice age, would it have necessarily have been isolated by water? I am not familiar with the exact geographical changes around the island of Flores, but I thought many of the land masses of Indonesia were connected prior to the end of the ice age 15,000 years ago.

By James Bass (not verified) on 28 Oct 2004 #permalink

Quoting Douglas Theobold's 29+ evidences for macroevolution prediction 2.5 under falsification:

"...we predict that we should never find elephants on any Pacific islands, even though they would survive well there."

Apparently finding elephants on Pacific Islands would be a falsification of macroevolutionary theory.

Quoting from this blog:

"Boats seem to have been essential for getting to Flores, which speaks of a pretty impressive mental capacity for Homo erectus . (On the other hand, lizards and elephants and other land animals got to the island without a boat--perhaps by swimming being swept away on logs during storms.)"

Whoops! One can imagine how a Creationist speaker would love to add this to his arsenal. First the evolutionists say that finding elephants on a remote Pacific island would "falsify" the theory, then, when elephants are found, the explanation is that they were swimming while holding on to logs in storms. Of course! The theory of evolution has been saved again!

By George McCurdy (not verified) on 28 Oct 2004 #permalink

Look at a map. Flores is not a 'remote Pacific island'; it is part of the 'Malay Archipelago'. No biogeographer would be more surprised to find elephants on Flores than rhinos on Sumatra.

Re James Bass's post: Why would it be useful to obtain mitochondrial DNA rather than DNA from a nucleus?
Re George McCurdy's comment: What sea level changes have there been in the area over the last 1 million years? Can he suggest an alternative to swimming there for H. floresiensis? Presumably to support the theory of evolution it would be necessary to demonstate that the DNA of H floresiensis has evolved from H. erectus?

By Andrew C Ross (not verified) on 28 Oct 2004 #permalink

It is much easier to extract mitochondrial DNA, because the mitochondrial genome is very short and there are lots of copies of it in each cell. As a result it's easier to amplify mtDNA and to be assured that it hasn't suffered post-mortem damage leading. Also, there are already mtDNA studies on Pleistocene Homo sapiens and Homo neandertalensis, so it would be interesting to see how more different Homo floresiensis is to these two species.

Hi Carl

Cool write-up. A few quibbles. Current best bet on the local extinction of H.floresiensis is the volcanic detonation that wiped out the other mini-mammals on the island c. 13,000 bp. If H.sapiens did in the hobbits then why did they leave the mini-stegodons and the like?

However from what the researchers who made the find have said the stone tools found with the homs are proportionately reduced from regular erectus-style tools - hence made for little hands. No evidence is yet apparent for a violent end, as much as certain paradigms are praying for such.

The intriguing aspect of the freshness of the remains are the local legends of "ebu gogo" who are described in terms very similar to H.floresiensis. Hence the current thought that the hobbits lived on until the arrival of the Dutch. Some - even Chris Stringer in "Nature" - have gone so far as to wonder if they're still lurking around the Javanese bush.

BTW the Scientific American link you gave has a link to an interview with Peter Brown. Here's his thoughts on the tools...

[Quote]B: It's strikingly different from everything ever found with H. erectus. Apart from this short, small-brained thing surviving until 14,000 or 18,000 years ago, its association with these stone tools is the other most remarkable thing about the site. It's something the critics will take a very close look at because there are three possibilities. Either Homo sapiens, of which there is no [fossil] evidence, was making these stone tools; or this small [hominid] learned to make the stone tools from H. sapiens in some way; or it was actually making the tools itself. I think it was making the stone tools. We have the same tools going from 94,000 years ago until 18,000 or 14,000 years ago--no change in technology, no change in materials, consistent from the bottom to where the skeleton was found. So on account of the evidence, the association seems fairly clear. Maybe something else will turn up at Liang Bua in the end, but at present there is nothing. The only [hominid] we're finding in association with stone tools is this small thing.[/Quote] Quite convincing linkage between the tools and the hobbits. What a puzzle!

i was just speaking with the flouridenthies in my backyard. to quote it: WE ARE ALL HOMO-ERECTUS DONT FLATTER YOURSELVES. THE SCIENTISTS ARE ALL A BUNCH OF HACKS AFRAID TO DISSECT ANY OF US CONTEMPORANEOUSLY AND ADMIT WE'RE ALL A LITTLE DIFFERENT! I'M NO ROCK HUDSON LOOK AT ME! in which moment i cut it off telling it not to be so hard on itself, and changing its attention back to the miniature stone tools that it was showing off to me.

By mark erectus (not verified) on 30 Oct 2004 #permalink

deep fried jungle monkeys.
sounds delicious.

It's a pity they don't actually have any H.erectus DNA to compare do they? I believe they have some Neanderthal DNA (which is H. sapiens).
Wouldn't it be good if they found them living today on other islands. They'd have to keep it a big secret though & vaccinate the little guys against everything.

Viva Orang Pendek!

The name literally means 'little man' in Bahasa Indonesia (maybe the same creature as ebu gogo?)...people at my field site in Borneo claim to have seen this small man-ape in the forest from time to time, although they question themselves as to whether they have just seen a gibbon walking on the ground!

You can bet that scientists all over the Indomalayan region are going to note the locations of previously unexplored caves. Although given the condition of these bones of H. floresiensis, one needs to tread lightly (or not at all without the help of an paleontologist)! There are literally thousands of islands in the region, so there must be other bones (and possibly hominid species) awaiting discovery.