It’s been a little over a year and a half now since scientists announced the discovery of the most controversial fossil in the field of human origins: Homo floresiensis a k a the Hobbit. Scientists found bones of a diminutive hominid on the Indonesian island of Flores, and estimated that it lived there as recently as 12,000 years ago. It stood about as high as a normal three year old human child and had a brain the size of a chimpanzee’s. But its bones were also found with stone tools.
The scientists declared the bones were not human. Instead, they belonged to a species of their own–one that branched off from much older hominids. Later, the scientists offered brain scans and more bones to bolster their case.
I’ve been chronicling the adventures of Homo floresiensis, trying to keep an eye out for new developments. My hobbit posts can be found here. In recent months the scientific reports have tapered off. That may be in part because of the ugly spat between rival paleoanthropologists over access to the bones and the site where they were found. Critics have been putting together attacks against the creation of a new species (most think the bones are from human pygmies, perhaps with birth defects). But those critical papers are slow in coming out.
Today we have the latest development in the hobbit wars, a critical paper from a team of American and British scientists and a response from the original team of scientists. They appear in the journal Science. I wish I could report some big surprising news, but these papers seem to be circling around two of the same questions that scientists have been asking for some time.
The new critical report comes from Robert Martin of the Field Museum in Chicago and his colleagues. The fact that Martin is not happy with the initial reports on Homo floresiensis is no secret. As I wrote last October, he was already working on his response back then, and Kate Wong at Scientific American offered some details in March. It’s still illuminating to look at his detailed comments in print.
There are two points to Martin’s complaint.
1. They picked the wrong human brain for their comparison. From the start, some critics argued that the hobbit was just a human with a case of microcephaly, a birth defect that produces a dramatically shrunken brain. Dean Falk of Florida State University led the effort to scan the brain case of Homo floresiensis, and for a point of comparison, she chose cast of a brain case of a microcephalic in the collection of the American Museum of Natural History. She concluded that the hobbit brain case looked less like that of a human microcephalic and more like the brain of Homo erectus, a six-foot tall hominid that appeared in Indonesia perhaps 1.8 million years ago.
Martin and his colleagues did a little detective work and discovered that the skull belonged to one Jakob Moegele, a German boy who died at age ten. Studying the original skull, they argued that it was a poor choice for a comparison. Moegele was a child, while the Hobbit was an adult. What’s more, his cranial capacity (272 cc) was very small for a microcephalic. Martin and his colleagues offered some sketches of a skull and two preserved brains of microcephalics that they claim are more similar to the Hobbit.
2. You can’t get a Hobbit by shrinking down Homo erectus. Lots of mammals have evolved from bigger to smaller–even elephants can become miniature. And by comparing related species of different sizes, scientists have gotten a rough idea of how their bodies change as they shrink. It turns out that bodies shrink faster than brains. As a result, small mammals have bigger brains relative to their bodies than big animals.
Martin and his colleagues used various formulas for brain and body dwarfing to predict what would happen if Homo erectus shrank down to Hobbit size. They found that its brain would have been far bigger than the actual size of Homo floresiensis’s fossil suggests. In fact, in order to get down to the Hobbit’s tiny brain, Homo erectus’s body would have to shrink down to a gram!
“We conclude,” Martin and his colleagues write, “that LB1 [the Hobbit fossil skull] was not an insular dwarf and may have been a microcephalic modern human.”
In the same issue of Science, Falk and her colleagues responded to both points.
1. Our scans beat your sketches. Falk and company point out a lot of shortcoming in the sketches Martin offers. The brain drawings lack crucial details about their structure, and the skull drawings are not accompanied by any information about what they look like inside. “Without this evidence,” Falk and company write, “the assertions of Martin et al remain unsubstantiated and difficult to address in further detail.”
2. Who said anything about a dwarf Homo erectus? Falk and her colleagues point out that while the brain had a Homo erectus-structure, they wrote that it “is too small to be attributed to normal dwarfing on H. erectus and further showed that its relative brain size is consistent with those of apes/australopithecines.” Australopithecines were an early wave of hominid species that lived from about 4.5 million to 2.5 million years ago. They could walk upright, but they were short and had brains not much bigger than a chimpanzee’s. And there’s no clear evidence from the fossil record that they ever left Africa. Homo erectus is among the earliest hominids to be found out of Africa.
That’s it. Frankly, I had a feeling of deja vu reading this material. Last October, I wrote about another attack in Science. Those critics had microcephalic brains of their own to show, but Falk argued that they also failed to analyze the brains in a consistent way. I wondered then, and I wonder now, why the editors of Science don’t make sure that everyone agrees on the ground rules for comparing these brains before they publish? Otherwise both sides just squabble about methods and presentation, rather than about meatier matters.
The problem may be that in both cases Science has relegated this exchange to the “Technical Comment” section, where reports are much shorter than normal papers. The descriptions of methods used in the research are often scant, and the comments also tend to include cryptic interpretations that cry out for more explanation. Falk and her colleagues say that the Hobbit’s brain is consistent with apes or australopithecines, not Homo erectus. Now, I’d imagine that this might imply that the Hobbit descends not from Homo erectus, but from some Australopithecine that came out of Africa. That would be huge news if true. Yet the scientists just leave us hanging with a statement that is so cryptic as to be nearly useless.
I hope that the debate doesn’t keep circling this way until someone finds a new fossil on Flores or some other Indonesian island. We hobbit junkies need a better fix.
Originally published May 18, 2006. Copyright 2006 Carl Zimmer.