Q. SPEAKING OF ISLANDS, WHEN AN APELIKE FOSSIL WAS DISCOVERED ON THE INDONESIAN ISLAND OF FLORES IN 2003, A GREAT CONTROVERSY BROKE OUT AMONG ANTHROPOLOGISTS. SOME SAID THIS THREE-FOOT TALL SMALL- BRAINED CREATURE WAS A NEW SPECIES OF HOMINID A HUMANLIKE PRIMATE. OTHERS CLAIMED IT WAS AN EARLY HUMAN WITH A BRAIN DEFORMITY. WHY DID YOU JUMP INTO THE FRAY?
A. Because I thought it was a hominid. This thing about its being a human ancestor with a diseased brain never made much sense. The people who insisted it was a deformed early human couldnt believe that it was possible to have such a huge reduction in brain size in any hominid. Yet, its possible to get a reduction in brain size of island animals as long as the selection pressure is there. Theres nothing to stop this from happening, even among hominids.
Q. SO WHY WERE OTHER SCIENTISTS INSISTING THAT FLORES MAN WAS A DEFORMED HUMAN?
A. Because theres this idea that nature moves inexorably towards bigger brains and some people find it very difficult to imagine why if you evolved a big brain as ancient hominids had why you would ever go back to a smaller one. But evolution doesnt really care. This smaller brain could have helped this species survive better than an energy-consuming bigger one. The insects have shown us this.
Maybe the summer heat is starting to get to me, but I find this totally arrogant. Has he taken the time to read any papers by anthropologists who are critical of the Homo floresiensis hypothesis? Niven here is saying that anthropologists believe in orthogenesis!
(UPDATE 2010-07-14: Gretchen asks if I’m turning into a crank. Wow, it really must be the heat getting to me! I have to keep reminding myself that press interviews frequently misrepresent the nuances of what scientists actually say and think. And yet, this stuff is widely read and believed even among our colleagues! Anyway, I’ve toned down some of the crankiness. )
Now, everybody knows that I’ve maintained almost total neutrality about Homo floresiensis here. I’ve skewered bad arguments on both sides, and tried to explain the best points in favor of both positions. I’m not a referee, and if I thought I had something useful to say, I’d publish a paper about it. I haven’t written much about it for the last year, because I don’t think that there’s been any newsworthy progress. Still, I know that a lot of people are interested.
What I notice is that when I write about this, I have to correct a lot of false claims about what the anti-floresiensis scientists have said. Why do I so rarely have to correct false claims about what the pro-floresiensis scientists say? This is a generalization, but I’ve written enough about this to have a good impression. The media reports skeptical arguments very poorly. I think it’s a systematic problem with science writing.
With the H. floresiensis issue, the science writers have been abetted by some careless scholars. A reporter may quote a pro-floresiensis scientist who says his critics believe something totally nonsensical, and they report that uncritically. This is another example of the same. I challenge anybody to find an anti-floresiensis scholar who has written that “nature moves inexorably towards bigger brains”.
It is quite obvious that smaller brains could have evolved in some ancient humans. That’s exactly what brains have been doing in several human populations for the last 10,000 years. Brain size is under stabilizing selection, and both energetic and ontogenetic demands favor smaller ones.
What critics point out is that the selection to reduce a brain to half or a third of its initial size must have been very strong. This is selection on the brain much stronger than selection on the size of the body. There are parallels where island species have reduced in relative brain size – that is, their brains have gotten smaller disproportionately compared to their bodies. But none are known to be anything like so extreme as Homo floresiensis would have to have been.
In other words, they argue that it may be reasonable to propose selection on smaller brain but Homo floresiensis is an extraordinary case compared to other mammals. And in their opinion extraordinary claims require more than one brain.
Why is Homo floresiensis different from insects, by the way? I can think of one important thing: Flores can hold billions of any species of insect, but at most thousands of hunter-gatherers. It is hard to optimize a complex system like the brain, reducing its energy consumption while maintaining its function. That task is vastly more difficult for evolution to accomplish when it has few mutations to work with. This is pretty basic population genetics – a small population is a lot more likely to evolve by breaking stuff than it is to optimize it.