The Errors of the Old Physical Anthropology

A reply to Vincent Sarich's article 'In Defense Of The Bell Curve'
(The Skeptic Vol.3 No.3:84-93)


Jeremy Genovese

Jeremy welcomes comments - send them to him at jgenovese@prodigy.net


Vincent Sarich's (1995) defense of The Bell Curve is at its heart a defense of the core ideas of the old physical anthropology that were in vogue until the middle of this century. These ideas include thecorrelation of brain size and intelligence, the existence of discrete racial taxons, and the necessity of ranking these taxons into a hierarchy.

There is no doubt that cranial capacity has increased substantially over the course of the evolution of the genus Homo. And noanthropologist doubts that this increase in brain size is related to the evolution of culture, a strategy of adaptation to the environment based on learned behaviors and symbolic communication (language).But paleoanthropologists often bemoan the fact that brains rarely fossilize, leaving them only with the occasional endocast and the crude statistic of cranial capacity as the data for making inferences about brain evolution (Tobias 1971). These data tell us little about the changes in the organization of the brain.

The phylogenetic increase in brain size is significant. But Sarich blurs the distinction between this fact a very different question. What is the significance of nonpathologic variation in brain size among modern Homo sapiens? The idea that brain size and intelligence are correlated has been marginalized in modern science not only as a result of revulsion at Nazi anthropology but also because this line of research has yielded so little of value.

Sarich's argument that people with bigger brains are, on the average smarter by virtue of those bigger brains(84) rests largely on Van Valen's 1974 paper 'Brain Size and Intelligence in Man'. Van Valen argued that all previous studies of the relationship between brain size and intelligence were really attempts to correlate imperfect measures of brain size (linear dimensions of the head, head circumference etc.) with imperfect measures of intelligence (IQ tests,grades and subjective evaluations). Of the eight studies Van Valen thought suitable the highest correlation was r=0.22. He speculated (that is he guessed) that if you could correlate brain size and intelligence directly the r value would be 0.3. Van Valen's paper was highly tentative and he did not present his results as anything more than speculation.

At this point it is worth remembering some basic facts about the meaning of correlation. Both Sarich and Van Valen use the correlation coefficient r rather than the coefficient of determination (R2). A standard work on regression tells us the relationship between the coefficient of determination, R2, and the estimate of the correlation coefficient, r, is straightforward:

R2=r2 [ie r squared]

This equality suggests a possible problem with r, which is a commonly used measure of strength of association. That is, r can inflate the importance of the relationship between X and Y. For instance, a correlation of .5 implies to the unwary reader that one-half of Y is being explained by X, since a perfect correlation is 1.0. Actually, though, we know that r=.5 means that X explains only 25% of the variation in Y (because r2=.25), which leaves fully three-fourths of the variation in Y unaccounted for. (The r will equal R2 only at the extremes, when r=+1 or 0.) By relying on r rather than R2, the impact of X on Y can be made to seem much greater than it is. Hence, to assess the strength of the relationship between the independent variable and the dependent variable, the R2 is the preferred measure (Lewis-Beck 1983 p. 25).

Thus the empirical study cited by Van Valen that show the highest correlation of 0.22 tells us that only 5% of the variation in intelligence can be explained in terms of head size. Two of the other empirical studies cited by Van Valen show r values of 0.08 which would mean that less than 1% of the variation in intelligence can be explained in terms of head size. These are not impressive results. The MRI study by Andreasen et. al. (1993) was much more moderate in its conclusion than Sarich indicates. The authors emphasized the modest nature of the relationships (132) they found. The authors did not confuse causation with correlation and they cautioned that this study does not permit any specific inferences concerning the influence or nature versus nurture on either brain growth or intelligence (133).

Do ethnic groups differ in brain size? Body size correlates very strongly with brain size. In table one I have regressed head circumference against stature for all available samples from anthropometric tables collected by NASA(1978). Head circumference is an imperfect measure of brain size, but it is the most widely used craniometric statistic, employed by pediatricians to evaluate brain growth in children. Stature is but one of several ways of assessing body size. Acknowledging these limitations, and making no judgments about causation, we see that 71% of the variation in head circumference can be explained in terms of variation in stature. In table two I have divided head circumference by stature to show fractional units of head circumference per unit of stature. To facilitate comparison I have transformed these values into Z scores using the arithmetic mean of the means. Notice that sample 10, Black enlisted Air Force Women, has a Z score of 2.44, that is over 2 SD above the mean. Bantu miners, sample 52, have a Z score of 0.51 above the mean and also higher than many European population. Sample 78 of white South Africans have a Z score of -0.71!

Sarich tells us with respect to the difference between American Whites and Blacks, the one good brain size study we have (Ho, et al., 1980) indicates a difference between them of about 0.8 SD(88). But in fact this study confirmed something found in almost all studies of brain weight and cranial capacity: The differences in brain size between men and women within the same ethnic group are greater than the differences between people of the same sex from different ethnic groups. Table three shows the findings of Ho and his colleagues for mean body height and mean body height. If Sarich's claims were true we would expect women to be less intelligent than men irrespective of ethnicity. Broca and other traditional craniometricians endorsed the idea of superior male intelligence linked to larger male brains (Russett 1989). It is more likely that most of the variation in brain size in modern humans can be explained by body size.

An even more fundamental issue raised by Sarich is the existence of races. Sarich is correct in pointing out that human variation is continuous and not discrete, but he claims we are justified in treating continuous variation as discrete the way we assign names to colors on the continuous light spectrum. One problem with this argument is that we know that the lines between so-called races are arbitrary and have been repeatedly redrawn through out history. On page 275 of The Bell Curve Hernstein and Murray (1995) make a curious observation that casts doubt on their whole enterprise. Here they tell us that the term Latino embraces people with highly disparate cultural heritages and a wide range of racial stocks. Many of these groups are known to differ markedly in their social and economic profiles. Add to that the problem of possible language difficulties with the tests, and generalizations about IQ become especially imprecise for Latinos.

At this point the careful reader is justified in asking why these caveats don't apply to the other ethnic categories used in The Bell Curve? East Asians include peoples speaking many different languages from many different cultures with divergent histories. African Americans constitute a hybrid population carrying genes from many different West African peoples as well as Europeans and Native Americans.

The unified category white is in some respects a recent invention. Psychometric and anthropological literature published before World War II almost always broke European populations into smaller ethnic distinctions. In this earlier literature it is not uncommon to read about the Nordic, Alpine and Mediterranean races or to see tables showing the IQ scores of different European immigrants to the United States. One such table appearing in a 1941 psychology text is reproduced here as table four (Garrett).

Sarich suggests that the existence of races is almost self evident. But when we look at how race has been constructed in the popular mind and in the law we find only a system of folk taxonomy. Human variation is a legitimate area of scientific study. But the term race with its connotation of Platonic typology is not a suitable framework for this study. Certainly some of the variation in our species is the result of adaptation to local selective forces and barriers to gene flow do exist. These barriers include geographic isolation and cultural differences. But people travel and cultures change. Humans are a wide-ranging species and gene flow between disparate populations has been an important characteristic of our evolution (Wolpoff 1980). Barriers to gene flow are continuously being breached and reconfigured. Ethnic group is a better term to describe interbreeding populations that resist gene flow through geographic isolation or mating rules. Ethnic groups have shifting boundaries, they come into existence and they fuse and dissolve into other populations. The term ethnic group allows us to recognize that these groups may have different gene frequencies than other such groups without making the mistake of casting these differences as the permanent features of some racial type.


Tables

Editor's Apology: Sorry, but I didn't have an HTML editor that did tables when I prepared this page, and I don't have time to code it up now,
so these are presented without formatting.


Table I

STATURE HEAD CIR

3 WAS PILOTS 1942 164.80 55.20
4 AAF NURSES 161.30 54.70
5 WAC SEPARATEE1946 162.22 55.16
6 WAF BASIC TR 1952 162.74 54.59
7 AIR FORCE WMN '68 162.10 54.87
8 WAF-NURSE OFCRS 162.77 55.20
9 ENLISTED WAFS/W 161.92 54.61
10 ENLISTED WAF/B 161.30 55.83
13 AIR TRAFFIC CNTRL 176.67 57.90
15 A.A.F. CADETS '42 176.30 57.00
16 A.A.F. GUNNERS '42 172.50 56.50
17 USAF BASIC TR '52 174.09 56.30
18 USAF FLY PRSNL'50 175.56 57.03
19 USAF SURVEY 1965 175.28 56.26
20 OFFICERS- - -1965 177.10 57.47
21 ENLISTED MEN'65 174.72 56.64
23 BASIC TRAINEE '65 175.07 55.88
24 NAVY FLYERS '64 177.64 57.54
25 USAF FLY PRSNL '67 177.34 57.52
26 STUDENT PLT '67 177.52 57.33
27 RATED PILOTS'67 177.39 57.67
28 SDT NAVIGAT '67 177.95 57.40
29 RTD NAVIGAT '67 176.99 57.38
30 ARMY SOLDIERS '66 174.52 56.11
31 NAVY ENLISTED '66 175.33 55.94
32 NAVY DIVERS '72 176.22 57.02
33 MARINE ENLIST '66 174.56 56.13
34 ARMY AVIATORS '59 176.52 57.12
36 ARMY AVIATORS '70 174.56 56.31
39 LAW ENFORCE OFFCR 178.07 57.50
46 JAPANESE CIV WMN 153.20 54.50
48 NATO SURVEY-60/61 170.22 55.86
49 TURKISH MIL'60 169.31 55.16
50 GREEK MILIT '61 170.50 55.65
51 ITALIAN MIL'61 170.62 56.51
52 BANTU MINERS 168.75 56.09
53 FRENCH ARMY 172.37 56.45
54 FRENCH PILOTS 175.60 56.75
55 FRENCH STUD PILOT 174.28 56.21
56 FRENCH NAVY I 171.64 55.92
57 FRENCH NAVY II 173.64 56.37
59 GERMAN AVIATORS 176.66 57.04
60 GERMAN 20 YR OLDS 175.80 57.00
61 GERMANS/25-40 YRS 174.50 57.30
62 CANADIAN MILIT'64 175.05 57.75
65 ROYAL ARMOR CORP 174.05 57.08
66 ROYAL AIR FORCE 177.44 57.67
67 RAF AIRCREW 176.96 57.94
68 RCAF PILOTS 177.44 57.30
69 RCAF NAVIGATORS 176.68 57.25
70 NEW ZEALAND AIRF 176.95 57.65
71 AUSTRALIAN CADETS 176.60 57.70
72 AUSTRALIAN RATED 176.80 58.30
73 CZECH LUMBERMEN 168.20 55.90
75 LATIN AMERICANS 167.00 55.00
77 FRENCH YOUNG MEN 171.99 56.64
78 SOUTH AFRICANS 175.31 56.75
79 JAPANESE CIV MEN 165.30 56.50
80 JAPANESE AIRFORCE 165.89 56.33
81 JAPAN AF PILOTS 167.35 56.52
82 JAPAN AF NAVIG 165.68 56.37
83 JAPANESE PILOTS 166.89 56.38
84 THAI MILITARY 163.40 54.00
85 VIETMAN MILITARY 160.43 54.07
86 R.O.K.A.F. PILOTS 168.66 55.97
87 KOREAN FORCES-65 165.20 54.40
90 IRANIAN MILITARY 166.85 55.29
91 AUSTRAILAN ARMY69 173.74 55.88

Head circumference regressed against stature for available NASA
(1978) samples.
r = 0.85 R2 = 0.71


Table II

HEAD CIR STATURE HC/STAT Z-score

3 WAS PILOTS 1942 55.20 164.80 0.334951 0.87
4 AAF NURSES 54.70 161.30 0.33912 1.45
5 WAC SEPARATEE1946 55.16 162.22 0.340032 1.58
6 WAF BASIC TR 1952 54.59 162.74 0.335443 0.94
7 AIR FORCE WMN '68 54.87 162.10 0.338495 1.37
8 WAF-NURSE OFCRS 55.20 162.77 0.339129 1.46
9 ENLISTED WAFS/W 54.61 161.92 0.337265 1.19
10 ENLISTED WAF/B 55.83 161.30 0.346125 2.44
13 AIR TRAFFIC CNTRL 57.90 176.67 0.32773 -0.15
15 A.A.F. CADETS '42 57.00 176.30 0.323313 -0.77
16 A.A.F. GUNNERS '42 56.50 172.50 0.327536 -0.17
17 USAF BASIC TR '52 56.30 174.09 0.323396 -0.75
18 USAF FLY PRSNL'50 57.03 175.56 0.324846 -0.55
19 USAF SURVEY 1965 56.26 175.28 0.320972 -1.09
20 OFFICERS- - -1965 57.47 177.10 0.324506 -0.60
21 ENLISTED MEN'65 56.64 174.72 0.324176 -0.64
23 BASIC TRAINEE '65 55.88 175.07 0.319187 -1.34
24 NAVY FLYERS '64 57.54 177.64 0.323914 -0.68
25 USAF FLY PRSNL '67 57.52 177.34 0.324349 -0.62
26 STUDENT PLT '67 57.33 177.52 0.32295 -0.82
27 RATED PILOTS'67 57.67 177.39 0.325103 -0.51
28 SDT NAVIGAT '67 57.40 177.95 0.322563 -0.87
29 RTD NAVIGAT '67 57.38 176.99 0.324199 -0.64
30 ARMY SOLDIERS '66 56.11 174.52 0.32151 -1.02
31 NAVY ENLISTED '66 55.94 175.33 0.319055 -1.36
32 NAVY DIVERS '72 57.02 176.22 0.323573 -0.73
33 MARINE ENLIST '66 56.13 174.56 0.321551 -1.01
34 ARMY AVIATORS '59 57.12 176.52 0.323589 -0.73
36 ARMY AVIATORS '70 56.31 174.56 0.322582 -0.87
39 LAW ENFORCE OFFCR 57.50 178.07 0.322907 -0.82
46 JAPANESE CIV WMN 54.50 153.20 0.355744 3.79
48 NATO SURVEY-60/61 55.86 170.22 0.328164 -0.08
49 TURKISH MIL'60 55.16 169.31 0.325793 -0.42
50 GREEK MILIT '61 55.65 170.50 0.326393 -0.33
51 ITALIAN MIL'61 56.51 170.62 0.331204 0.34
52 BANTU MINERS 56.09 168.75 0.332385 0.51
53 FRENCH ARMY 56.45 172.37 0.327493 -0.18
54 FRENCH PILOTS 56.75 175.60 0.323178 -0.78
55 FRENCH STUD PILOT 56.21 174.28 0.322527 -0.88
56 FRENCH NAVY I 55.92 171.64 0.325798 -0.42
57 FRENCH NAVY II 56.37 173.64 0.324637 -0.58
59 GERMAN AVIATORS 57.04 176.66 0.32288 -0.83
60 GERMAN 20 YR OLDS 57.00 175.80 0.324232 -0.64
61 GERMANS/25-40 YRS 57.30 174.50 0.328367 -0.06
62 CANADIAN MILIT'64 57.75 175.05 0.329906 0.16
65 ROYAL ARMOR CORP 57.08 174.05 0.327952 -0.11
66 ROYAL AIR FORCE 57.67 177.44 0.325011 -0.53
67 RAF AIRCREW 57.94 176.96 0.327419 -0.19
68 RCAF PILOTS 57.30 177.44 0.322926 -0.82
69 RCAF NAVIGATORS 57.25 176.68 0.324032 -0.66
70 NEW ZEALAND AIRF 57.65 176.95 0.325798 -0.42
71 AUSTRALIAN CADETS 57.70 176.60 0.326727 -0.29
72 AUSTRALIAN RATED 58.30 176.80 0.329751 0.14
73 CZECH LUMBERMEN 55.90 168.20 0.332342 0.50
75 LATIN AMERICANS 55.00 167.00 0.329341 0.08
77 FRENCH YOUNG MEN 56.64 171.99 0.329321 0.08
78 SOUTH AFRICANS 56.75 175.31 0.323712 -0.71
79 JAPANESE CIV MEN 56.50 165.30 0.341803 1.83
80 JAPANESE AIRFORCE 56.33 165.89 0.339562 1.52
81 JAPAN AF PILOTS 56.52 167.35 0.337735 1.26
82 JAPAN AF NAVIG 56.37 165.68 0.340234 1.61
83 JAPANESE PILOTS 56.38 166.89 0.337827 1.27
84 THAI MILITARY 54.00 163.40 0.330477 0.24
85 VIETMAN MILITARY 54.07 160.43 0.337032 1.16
86 R.O.K.A.F. PILOTS 55.97 168.66 0.331851 0.43
87 KOREAN FORCES-65 54.40 165.20 0.329298 0.08
90 IRANIAN MILITARY 55.29 166.85 0.331375 0.37
91 AUSTRALIAN ARMY69 55.88 173.74 0.32163 -1.00

MEAN= 56.38 171.59 0.33
SD= 1.04 5.83 0.01

Z transformations for head circumference to stature ratios for
available NASA (1978) samples.



Table III

No. of Cases Mean Body Height / cm Mean Brain Weight / g

White Males 414 175 1392
Black Males 225 173 1286
White Females 388 162 1252
Black Females 218 162 1157

Brain weight and stature from Ho et. al (1980).




Table IV

Nationality No. Av. IQ

Polish Jews 75 102.80
Swedes 232 102.10
English 213 100.70
Russian Jews 627 99.50
Germans 190 98.50
Lithuanians 468 97.40
Irish 214 95.90
British Canadians 115 93.80
Russians 90 90.00
Poles 227 89.60
Greeks 270 87.60
Italians 350 85.80
French Canadians 243 85.30
Portuguese 671 82.70

Mean IQs of children of immigrant groups from a 1941 psychology text
(Garrett).



Bibliography

Andreasen, N. C., M. Flaum, V. Swayze, D. D. OLeary, R. Alliger, G.
Cohen,J. Erhardt, and W. T. C. Yuh. 1993. Intelligence and Brain
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Garrett, H. 1941. Great Experiments In Psychology. New York:
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Hernstein, R. J. and C. Murray. 1995. The Bell Curve New York: Free
Press.

Ho, K. C., U. Roessmann, J. V. Straumfjord, and G. Monroe. 1980.
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Lewis-Beck, M. S. 1980. Applied Regression. Beverly Hills: Sage.

NASA. 1978. Anthropometric Source Book: Vol. 2. A Handbook of
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Van Valen, L. 1974. Brain Size and Intelligence in Man. American
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Wolpoff, M. 1980. Paleoanthropology. New York: Knopf.

 

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