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Two neuroscientists say that a now-extinct race of humans had big eyes, child-like faces, and an average intelligence of around 150, making them geniuses among Homo sapiens.
We have seen reports of Boskop brain size ranging from 1,650 to 1,900 cc. Let’s assume that an average Boskop brain was around 1,750 cc. What does this mean in terms of function? How would a person with such a brain differ from us? Our brains are roughly 25 percent larger than those of the late Homo erectus. We might say that the functional difference between us and them is about the same as between ourselves and Boskops.
Expanding the brain changes its internal proportions in highly predictable ways. From ape to human, the brain grows about fourfold, but most of that increase occurs in the cortex, not in more ancient structures. Moreover, even within the cortex, the areas that grow by far the most are the association areas, while cortical structures such as those controlling sensory and motor mechanisms stay unchanged.
Going from human to Boskop, these association zones are even more disproportionately expanded. Boskop’s brain size is about 30 percent larger than our own—that is, a 1,750-cc brain to our average of 1,350 cc. And that leads to an increase in the prefrontal cortex of a staggering 53 percent. If these principled relations among brain parts hold true, then Boskops would have had not only an impressively large brain but an inconceivably large prefrontal cortex.
Even if brain size accounts for just 10 to 20 percent of an IQ test score, it is possible to conjecture what kind of average scores would be made by a group of people with 30 percent larger brains. We can readily calculate that a population with a mean brain size of 1,750 cc would be expected to have an average IQ of 149.
This is a score that would be labeled at the genius level. And if there was normal variability among Boskops, as among the rest of us, then perhaps 15 to 20 percent of them would be expected to score over 180. In a classroom with 35 big-headed, baby-faced Boskop kids, you would likely encounter five or six with IQ scores at the upper range of what has ever been recorded in human history.
First of all claiming they were smarter than us requires extraordinary evidence (which there is none).
Thirdly, brain size and intelligence don't show perfect correlation.
Even if brain size accounts for just 10 to 20 percent of an IQ test score, it is possible to conjecture what kind of average scores would be made by a group of people with 30 percent larger brains. We can readily calculate that a population with a mean brain size of 1,750 cc would be expected to have an average IQ of 149.
As I recall, Neanderthals had much bigger brains than us, but still e.g. their tools were rather undeveloped in comparison to H. sapiens tools of the time..
Secondly, a brain 30% larger than the average human brain uses something like 200 - 300% more energy. Somehow, I don't see this as a winning combination in times of energy scarcity.
The portrayal of "Boskops" in the Discover excerpt is so out of line with anthropology of the last forty years, that I am amazed the magazine printed it. I am unaware of any credible biological anthropologist or archaeologist who would confirm their description of the "Boskopoids," except as an obsolete category from the history of anthropology.
[UPDATE (2010-01-04): I have heard from Amos Zeeberg, the Web editor at Discover. He writes that the excerpt was intended to run identified as a "controversial idea, but that context didn't come across as intended." The web page has been changed to make that context clear, and to link to my discussion here. I think it's great that he responded so quickly, although I think that this case is not controversial, it's non-science. ] Besides that, the authors make several questionable statements about the relative sizes of parts of the brain and their relation to cognition and behavior in ancient hunter-gatherers.
IQ of fossils
We have no credible way of estimating the IQ of a fossil skull. The excerpt claims:
Even if brain size accounts for just 10 to 20 percent of an IQ test score, it is possible to conjecture what kind of average scores would be made by a group of people with 30 percent larger brains. We can readily calculate that a population with a mean brain size of 1,750 cc would be expected to have an average IQ of 149.
First of all, there never was any human population with a 1750 cc average brain size.
Now, taking the counterfactual: A regression equation within a population can predict an expected value for an individual within that population. But in population genetics, the average IQ that we would predict for a population with a 1750 cc average, depends on how the brain got to be that size. Natural selection on intelligence or brain size would have altered the relation that holds within humans. Nor do we know whether the present-day correlation would have characterized any ancient population -- or indeed most living human populations. The current value in Europeans may be an artifact of Holocene genetic changes.
The authors do not list the specific regression that they use, or its source. The correlation relates to the proportion of variance explained by the relation of brain size and intelligence is irrelevant to this prediction. What we want to know is the slope of the regression. The prediction here would require a slope of 0.14, assuming it had been derived from a population with a mean male volume of 1400 cc and an average IQ of 100. That's a higher slope than I've seen reported in any analysis of the brain size - IQ relationship.