race

OK, so I can't say it's not "brain science" because measuring skulls is as close to brain science as anthropology ever gets. But it just shouldn't be that hard to measure volume. It's a simple physical fact.

Sure, there are complexities in measuring the volume of an object with a complicated shape and holes, like a human skull. But this is not one of the world's great mysteries. Seal the holes, fill the skull with beads or shot or something, and pour it into a graduated cylinder. Junior high stuff.

Samuel Morton became famous in the mid 19th century as an empirical scientist for measuring the skulls of people from different parts of the world. Stephen Jay Gould claimed, first in Science in 1978 [1] and later in his book The Mismeasure of Man [2], that Samuel Morton fudged his data on skull volumes. In Gould's telling, Morton began with a strong bias toward finding that Caucasians were the superior race and made several choices in measurement and reporting statistics that tended to confirm this bias. Gould's biggest claims, in a statistical sense, were fairly obscure statistical points about the tabulation of averages and treatment of subpopulations as compared to major race groups. One claim, however, was more memorable than all the rest -- the notion that Morton used seed to measure the skulls and packed it in harder with his thumb to increase the measured volume of "White" skulls.

Most people probably suppose Gould to have been an expert on the Morton collection, but in fact he never examined or measured the crania himself. A new paper in PLoS Biology by Jason Lewis and colleagues [3] accomplishes what no one else did in the succeeding 30 years (despite one earlier attempt): they checked Gould's facts. They find that again and again, Gould misstated the evidence or simply made stuff up.

This is an important paper. The authors wrote in an even tone and lay out the facts in a very straightforward way. As a reader, I can't see how they managed to keep their cool. Some of Gould's mistakes are outrageous, with others it is hard for me to believe that the misstatements were not deliberate misrepresentations.

For example, let's take the story about pushing seed into the skulls. Here is a paragraph from Lewis and colleagues, with direct quotes from Gould:

Gould famously suggested that Morton's measurements may have been subject to bias: “Plausible scenarios are easy to construct. Morton, measuring by seed, picks up a threateningly large black skull, fills it lightly and gives it a few desultory shakes. Next, he takes a distressingly small Caucasian skull, shakes hard, and pushes mightily at the foramen magnum with his thumb. It is easily done, without conscious motivation; expectation is a powerful guide to action” [5]. While Gould offers this as only a “plausible scenario,” and did not remeasure any crania, subsequent authors have generally (and incorrectly) cited Gould as demonstrating that Morton physically mismeasured crania (e.g., [15]).

In other words, Gould made up the whole thing. It was an utter fabulation. It is disgraceful that later authors have cited this idea as fact.

When Lewis and colleagues examined Morton's numbers they found that there had been no bias in the direction Gould claimed. Measurements from seed had greater error than those from lead shot, in part (as Morton himself had written) because he employed an assistant for seed measurements early on, but later did these personally with shot.

Moreover, Lewis and colleagues systematically remeasured the volumes of a sample comprising half of the skulls Morton measured, and found no systematic bias, with the few deviations in Morton's data actually in the direction opposite his supposed bias.

With numbers like these, it is natural to wonder exactly where Gould came up with his idea that Morton's numbers were fudged. Here's how: Gould fudged his own numbers! I'm quoting here a long passage from the paper, because it is essential to understand Gould's full perfidy.

Gould also performed his own analysis of Morton's cranial capacity data and came to the conclusion that “there are no differences to speak of among Morton's races” ([1], italics in original). For Morton's 1839 seed-based measurements, Gould claims that Morton's Native American average capacity is artificially depressed by his inappropriate use of a straight mean (taking the average of each individual specimen in the entire sample) rather than a grouped mean (first taking the average of each Native American population subsample, then calculating the mean of those means), since the former is sensitive to differences in sample sizes between “large headed” populations and “small headed” populations. In fact, the grouped mean for Morton's Native American dataset is 79.9 in³, almost identical to the straight mean of 80.2 in³ (Dataset S3). So Morton's use of a straight mean actually slightly increased his Native American average. Gould's calculation of a higher Native American average (83.8 in³) is entirely a function of Gould omitting 34 crania (of 144) as coming from populations with samples of n

Gould's reanalysis of Morton's 1849 shot-based data resulted in a Native American mean capacity of 86 in³ rather than Morton's original 79 in³ [1]. Gould obtained his new average by again taking the group mean of Native American populations with four or more crania. But Gould also applied an additional restriction: he only included Native American crania that Morton had also previously measured with seed. This restriction is entirely arbitrary on Gould's part, as Morton's publications and analyses for his seed- and shot-based measurements are completely separate (1839 versus 1849), and Gould did not apply this restriction to the other groups he reanalyzed in Morton's shot-based data. If this restriction is lifted, Gould's Native American average would be reduced to about 83 in³, considerably below his reported 86 in³ (Dataset S3).

Here is the most sympathetic reading I can give to these facts. Gould systematically selected data from Morton's tables that tended to inflate the measured volumes of Native American crania. He did so by averaging some group means instead of overall means (although Lewis and colleagues show that Morton himself had used group means for many comparisons, contrary to Gould's claims), by excluding some small-skulled groups entirely (claiming sample size as a criterion), and by omitting crania that had not been measured in the earlier, seed-based analysis. There is no logical reason for these choices other than selection bias -- Gould began with a conclusion about Morton's unconscious motivations, and worked to confirm that conclusion by selecting some data and omitting contrary data.

Anyway, you can see why I find this outrageous. Gould used the well-documented work of a long-dead man to make an argument that unconscious bias is widespread in science. He posed as a concerned critic, but thereby cast doubt on the validity of the scientific enterprise. He picked volume measurement and tabulation of averages as his target, making it seem as if the simplest and most objective observations -- the Junior High-level science methods -- were themselves subject to all-encompassing cultural biases. His paper and book are very widely read and cited by people who will never examine the primary evidence. Gould owed us a responsible reading and trustworthy reporting on that evidence. In its place, he made up fictional stories, never directly examined the evidence himself, and misreported Morton's numbers.

This stuff really ticks me off. I don't think that Gould's errors can be written off as "unconscious bias". Reading back over his 1978 article, I cannot believe that Science published it.

The new paper is open access ("The Mismeasure of Science: Stephen Jay Gould versus Samuel George Morton on Skulls and Bias"), and I think that everyone should read it. The text is easy to follow, and the authors include clear answers to common questions about Morton's work and beliefs. It is a very suitable article for assignment in classes. They note that the basic issue here (endocranial volume of different groups) is largely explained by ecogeography -- the authors mention climate explicitly, but I would add body size and life history as parameters that covary with climate. Measurement of endocranial volume was cutting edge science in 1840, but I repeat, this is simple stuff.

References

Blaine Bettinger (the Genetic Genealogist) writes that some commercial test offerings are trying to sort out a way to tell you how Neandertal you are:

Once [the Max Planck] study came out, I knew it was only a matter of time before companies began offering tests that examined the percent of Neanderthal contribution to a test-taker’s genome.

This is one of the stickiest places to be a blogger. Bettinger links to a testing company's information on its product (including promotion of "Neandertal themed art" for the customer, sold at their Las Vegas gallery). Others have linked to Bettinger, drawing more attention.

I think that as a scientist, more promotion is the last thing I should be giving this company. So I won't be naming or linking to their advertising.

Ironically, the promotional material does not make any false statements of fact. The material makes it perfectly clear that the product does not test any gene variants that scientific research has shown may have come from Neandertals. Instead, the product reports on gene variants that we don't know about from Neandertals.

Huh?

You may wonder how a company can market such a product as a "Neanderthal Index". Since "Neanderthal Index" is not a scientific concept, a company can claim whatever it wants.

So what is it? According to the material, the Neanderthal Index is computed from (a very few) STR alleles shared with "archaic" populations. Those "archaic" populations aren't Neandertals, they're Basques, Turks, Syrians, and other living people. Anthropologists do not call these people "archaic", so this is not a scientific concept either. Nobody has demonstrated that the listed populations are more or less Neandertal-like than any other living people. Most of the differences between these living populations emerged during the last 10,000 years.

You'd do better putting calipers on your skull and measuring your cephalic index. At least that would tell you whether some real phenotype is Neandertal-like.

I don't imagine that customers beating down the doors for this product. I think it exists as a way of bringing attention -- Neandertals are in the headlines. That's a big reason to not give them any attention. The test has nothing whatsoever to do with Neandertals as we scientifically understand them.

Can you tell that I'm disgusted by this?

Here in my lab, we're in a very good position to say that no test today can accurately report on your individual proportion of Neandertal ancestry. Until we have characterized a broader set of gene trees than we have so far, we are really not able to give any answer about how similar any person's genome is to Neandertals. We can't say yet how heterogeneous the human population is today in its ancestry from different parts of the world during the Late Pleistocene. For the past thirty years most working geneticists completely ignored the possibility of such heterogeneity, we are only just beginning to investigate it seriously.

This kind of thing may not be why the FDA is looking to regulate personal genomics. Neandertal ancestry is not directly relevant to health. But if customers buy tests like this thinking that they are learning about Uncle Thag, just how much misinformation will they accept from other tests that purport to tell them something more important?

Oh, good grief!

[post UPDATED]

I have had an unusual number of hits the past few days, so I went through my logs looking for the source. Turns out people are reading my 2008 review of the "Boskops race"("The 'amazing' Boskops").

Over 10,000 people have read that post since the New Year began. That post has always gotten a recurring readership, because of a 2008 book by Gary Lynch and Richard Granger, Big Brain: The Origins and Future of Human Intelligence.

Evidently the book is about to come out in paperback. And Discover magazine, which gave the book a fairly positive review on its release, has now reprinted an excerpt detailing the wondrous features of the Boskops race ("What Happened to the Hominids Who Were Smarter Than Us?"). Someone copied the whole thing to Richard Dawkins' website. And people reading the excerpt are trying to find out more about this fantastic story, and finding my blog.

Well, to all those seeking the light of paleoanthropology, welcome!

To those who have linked the post: I want to let you all know that your links have directed more than 10,000 people to find some actual true information about the "Boskop race". Good work out there!

What can I do to update people, now that this story is spreading once again? My original post gives a short history, but was not based on a real review of the book. I was just trying to get some accurate information out there.

Now I have read the excerpt, and much (but not all) of the Boskop-related text in the book (courtesy of Amazon).

It's worse than I feared. The excerpt actually presents 1920's-era anthropology as if it were the state of our knowledge about Boskop and the "Boskop race" today. I have not found any passages in the book or chapter notes that contradict the excerpt's portrayal. I cannot find references or citations of post-1940 research on skeletal remains or archaeology from southern Africa. There's no hint of what happened after archaeologists began to use radiocarbon dating, nor do we hear even the identity of any specimens, except for the original (and fragmented) Boskop skull itself.

How can this be? From the book's notes, it appears that the authors didn't find any information on these topics:

One of the oddities in the Boskop story is the disconnect between the rich trove of references from the early twentieth century, and the paucity of references after that time (Lynch and Granger 2008: 218).

I find that very sad, because there is a much richer trove of references after 1958. Archaeologists have developed a deep understanding of the chronology and material culture of LSA and later hunter-gatherers around the Cape and northward. Skeletal biologists have studied the health status, demography, and morphology of Holocene and earlier peoples. Some have even examined the endocranial volumes of southern African skeletal samples, and have tested the hypothesis of trends in brain size over time.

All this work shows a very different picture than that sketched by Lynch and Granger.

I'm going to be very measured, because while I am often snarky, I rarely come straight out and write that something is bunk. 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.

The "inconceivable" prefrontal cortex

We know little about the relative sizes of cortical areas in fossil hominins. The excerpt claims that the prefrontal area of a Boskop must have been "inconceivably large"

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.

First of all, there was never any human population with an 1750 cc average brain size.

Again, the example is a misapplication of regression, in this case an among-species regression. The excerpt appears to assume that the evolution of relative prefrontal area among human populations must have followed the same disproportionate pattern of increase as that between humans and chimpanzees. Prefrontal cortex volume is larger, relative to brain size, in humans compared to other primates. But this relation is not very much larger in humans -- recent estimates range from less than 10 to 30 percent compared to chimpanzees (Holloway 2002, Schoenemann et al. 2005). Even if some ancient humans had a second burst of expansion, again as great as that on the hominin lineage leading from apes to us, their prefrontal volume would hardly be "inconceivably large".

And there's no reason at all to assert such a second, bonus expansion of prefrontal area in ancient humans. The prefrontal area ought to scale close to the total brain size, as it does within living people.

Science fiction

The authors actually cite and discuss Loren Eiseley's Immense Journey, which I discussed in my earlier post. Eiseley was a naturalist/anthropologist/science writer, and a very popular essayist -- he's the kind of person we could use more of today. But his reflections on the "Boskop people" were a fictional trope -- and were already, in 1958. He was a great writer, but relying on Eiseley for up-to-date information on anthropology is like relying on Truman Capote as an authority on crime.

Suppose that we take the "Boskops" story just as a science fiction fairy tale -- a story showing that evolution is not synonymous with progress, as the authors imply. I still conclude that much of the other information about brain size in the excerpt is questionable or false.

The authors speculate:

Our big brains give us such powers of extrapolation that we may extrapolate straight out of reality, into worlds that are possible but that never actually happened.

That's Boskop, all right. Extrapolated straight from worlds that never happened!

References:

Broom R. 1918. The evidence afforded by the Boskop skull of a new species of primitive man (Homo capensis). Anthropol Pap Am Mus Nat Hist 23 (2):63-79.

Brothwell DR. 1963. Evidence of early population change in central and southern Africa: Doubts and problems. Man 63:101-104.

Dart R. 1923. Boskop remains from the south-east African coast. Nature 112:623-625.

Dubow S. 1996. Human origins, race typology and the other Raymond Dart. African Studies 55:1-30.

Henneberg M, Steyn M. 1993. Trends in cranial capacity and cranial index in Subsaharan Africa during the Holocene. Am J Hum Biol 5:473-479.

Holloway RL. 2002. How much larger is the relative volume of area 10 of the prefrontal cortex in humans? Am J Phys Anthropol 118:399-401. doi:10.1002/ajpa.10090

Pycraft WP. 1925. On the calvaria found at Boskop, Transvaal, in 1913, and its relationship to Cromagnard and Negroid skulls. J Roy Anthropol Inst 55:179-198.

Schauder DE. 1963. The anthropological work of F. W. FitzSimons in the Eastern Cape. S Afr Archaeol Bull 18:52-59.

Semendeferi K, Armstrong E, Schleicher A, Zilles K, Van Hoesen GW. 2001. Prefrontal cortex in humans and apes: a comparative study of Area 10. Am J Phys Anthropol 114:224-241.

Singer R. The Boskop "race" problem. Man 58:173-178.

Singer R. 1962. Presidential Address 1962: The South African Archaeological Society: The future of physical anthropology in South Africa. S Afr Archaeol Bull 17:205-211.

Stynder DD, Ackermann RR, Sealy JC. 2007. Craniofacial variation and population continuity in the South African Holocene. Am J Phys Anthropol 134:489-500. doi:10.1002/ajpa.20696