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Corrections to a paper on race and sex differences in brain size and intelligence
Abstract
This paper presents two corrections to an earlier paper by Rushton (Personality and Individual Differences, 11, 785–794, 1990). The first is to the equation used to calculate cranial capacities from externally measured head sizes. Eleven millimeters should be subtracted from head length and width for fat and skin around the skull. When the subtractions are made the cranial capacities for the different races are about 200 cm3 smaller than previously reported, although the significant rank ordering of Mongoloids > Caucasoids > Negroids is preserved. The second correction is to the statement that there are no sex differences in brain size when body size variables are controlled. Two recent studies using large data sets show that after covariance adjustment for body size, women's brains average 100 g lighter and 110 cm3 smaller than men's. These findings are best understood from the perspective of human evolution.
... While conceding``conceding``that there might be a very modest relation between head size and measured intelligence'' (p. 119), K&O speci®cally challenged the ®ndings of Black±White dierences in cranial size estimated from external head measures (by Jensen, 1994;Jensen & Johnson, 1994;Lynn, 1990Lynn, , 1993Rushton, 1992Rushton, , 1993Rushton, , 1994Rushton & Osborne, 1995). K&O claimed signi®cant errors in the published results, and reported that although American Whites have greater head height than American Blacks, Blacks have greater head length and greater head circumference. ...
... 261± 264), although they reported there was no obvious way of subtracting for fat and skin. Subsequently, Rushton (1993) and K&O (1998) amended Eqs. (3)±(6) by subtracting 11 mm for fat and skin around the skull, and Jensen and Johnson (1994, p. 319 , Table 6) modi®ed Lee and Pearson's Eqs. ...
... (1) and (2) using both White and East Asian military samples. Rushton (1993) found results within 25 cm 3 (less than 2% dierence) from those obtained using the panracial equations. Further, K&O's use of the Ainu Eqs. ...
We provide a case by case examination of Kamin and Omari’s critical review (South African Journal of Psychology, 1998, 28, 119–128) concluding that race differences in head size were too small to explain their differences in IQ. Although Kamin and Omari make several valid points and identified an “anomalous” finding in two samples (that Blacks averaged greater head circumference than Whites), in the main their review is highly misleading. We find, among other things, that Kamin and Omari: (1) ignored the relation between brain size and IQ established by magnetic resonance imaging and the race differences in brain size established by MRI, autopsies, and endocranial volume; (2) erred in attributing to arithmetic errors and uncontrolled differences in sex ratio the differences in head size found from birth to age seven in the National Collaborative Perinatal Project; (3) neglected data showing that young Black girls mature faster than White girls which explains why Black girls sometimes average cranial sizes equal to or greater than their White age peers; and (4) seized upon ad hoc “alternative” findings and explanations for particular studies. When the principle of aggregation is employed and data averaged across the numerous studies, the race differences in average cranial capacity clearly emerge. New analyses in this article also confirm that whereas Blacks average proportionately longer heads, Whites and Asians average proportionately wider and higher heads, which explains why different equations for estimating cranial volume sometimes produce different results. We conclude that brain volume bears a strong relation to cognitive ability, and that increasing encephalization over evolutionary time led to progressively more spherically shaped heads with corresponding increases in head width and head height.
... The second (Rushton, 1992) demonstrated that even after adjusting for the effects of body size, sex, and military rank in a stratified random sample of over 6,000 U.S. Army personnel, the average cranial capacity of East Asians, Whites, and Blacks were 1,416, 1,380, and 1,359 cm 3 , respectively. The third study (Rushton, 1993) reanalyzed a set of anthropometric data originally published by Melville Herskovits (who concluded there were not race differences in cranial capacity) and found Whites averaged a cranial capacity of 1,421 and Blacks, 1,295 cm 3 . The fourth study (Rushton, 1994) analyzed data obtained on tens of thousands of people from around the world collated by the International Labor Office in Geneva, Switzerland. ...
... Brain and endocranium sexual dimorphism Since Raisman and Field (1971) demonstrated that the brain could be a sexually dimorphic structure, this issue has been extensively addressed in several studies (DeLacoste-Utamsing and Holloway, 1982;Ankney, 1992;Rushton, 1993;Lynn, 1994). However, this was not always done from an objective point of view (Swaab and Hofman, 1984;Hofman and Swaab, 1991), and frequently abusive conclusions were drawn about dierences in intelligence between sexes based on morphological evidences. ...
Human phylogenetic history is directly related to brain evolution. But many biologic processes related to the appearance of this complex organ are unknown, mainly due to the fact that it is an organ composed of soft tissue, which is not sensitive to the fossilization processes. Hence, to infer human brain evolution it is essential to study the indirect evidences it leaves in the cranial bones, such as the endocranial size (cranial capacity) and shape. In this sense, the hominid fossil record has an important cranial representation in relation to other bones. However, in order to interpret the information the cranium provides about the brain it shelter and infer evolutive theories, it is vital to understand the relationship between the brain and the endocranial vault. In this PhD, modern human endocranium and brain growth and development will be characterized from a morphometric point of view, with the aim of defining how these two structures interact and correlate throughout maturation from birth to adulthood. This body of knowledge will be applied to enlighten our interpretations of the different indirect evidences we have about the human brain evolution. In this way, the present thesis research will not only contribute to our understanding of brain evolution in the human lineage, but it will also assist future medical research that investigate human brain and cranial growth and development trajectories. In order to answer these questions two data bases were created: one of them consisting of computed tomographic (CT) images to study bone structure maturation, and the other one consisting of magnetic resonance (MR) images to quantify ontogenetic changes in the soft brain tissue. These data bases contain individuals in a range from birth to the age of 31. The data was analysed by means of geometric morphometric techniques, which allow the statistic separation of size and shape changes throughout ontogeny, in this particular case. The results showed that the brain and endocranium present a close ontogenetic relationship from birth to the first adolescence (approximately to the age of 10 in females and 12.5 in males). From this time onwards the brain starts loosing volume (mainly gray matter due to neuronal rearrangements), and therefore, the close relationship between brain cortex and endocranial vault gradually diminishes, at the same time that the brain modifies its shape. For this reason, brain shape changes from adolescence onwards are not rejcted in endocranial regions. An important contribution was the construction of accurate and precise brain / endocranial volume (BV/ECV) ratio formulas dependent of sex, age and endocranial size, which may serve to extract better information from cranial data. A third main subject of this PhD was the study of asymmetric patterns in both brain and endocranium. In this sense, it was shown that the brain macroscopic asymmetries and the endocranial petal pattern are not the same for the different periods analysed, and they even change their trajectories through ontogeny. Hence, the adult asymmetric patterns are not the same than in the sub-adults. Finally, sexual dimorphism was investigated in both structures, and the characterization of growth and development divergences between females and males could be done through heterochonic processes. Growth and development of the brain and its surrounding bony endocranial tissue could be characterized in the human species, with the aid of 3D medical images and new geometric morphometric techniques specially developed for this study. New information about the ontogenetic relationship between these two structures was discovered,
constituting an important tool that will enlighten human studies about brain evolution.
... Cranial volume was calculated according to the formula: (7.884*(head length À11)+10.842)*((head width À11) À1593.96))); units in mm [37]. Data for infant mortality (i.e. ...
Secular increase in human height and performance occurred in Europe throughout the 20(th) century despite the temporally worsening access to nutrients during and after WWII. This pattern is paradoxical under the assumption of the major impact of pre- and post-natal growth conditions for determination of adult size and human capital.
We examined the anthropometric parameters of Estonian girls born between 1938 and 1953, and measured around the age of 17 (n = 1475). This period involved two opposite trends in the economic and epidemiological situation: increasing birth-time economic hardships during the war and particularly in the post-war period, and decreasing infant mortality (a proxy of disease burden) after 1947.
Height of girls was negatively affected by the number of siblings and positively by parental socioeconomic position, but these effects were weaker than the secular trend. Leg length (an indicator of pre-pubertal growth conditions) was independent of age and birth date while all other traits, including measures of performance (cranial volume, lung capacity and handgrip strength) showed acceleration. The best predictor of size at age 17 was, in most cases, infant mortality in the year when the girls were aged 11.
Reduction of disease burden during pubertal growth can override effects of resource shortage at birth. Our results also support the idea that increasing efficiency of pathogen control can contribute to the secular increase in cognitive abilities, i.e., the Flynn effect, and that epidemiological transition is the main driver of secular increase in human capital.
© The Author(s) 2015. Published by Oxford University Press on behalf of the Foundation for Evolution, Medicine, and Public Health.
... The second (Rushton, 1992) demonstrated that even after adjusting for the effects of body size, sex, and military rank in a stratified random sample of over 6,000 U.S. Army personnel, the average cranial capacity of East Asians, Whites, and Blacks were 1,416, 1,380, and 1,359 cm 3 , respectively. The third study (Rushton, 1993) reanalyzed a set of anthropometric data originally published by Melville Herskovits (who concluded there were not race differences in cranial capacity) and found Whites averaged a cranial capacity of 1,421 and Blacks, 1,295 cm 3 . The fourth study (Rushton, 1994) analyzed data obtained on tens of thousands of people from around the world collated by the International Labor Office in Geneva, Switzerland. ...
The culture-only (0% genetic-100% environmental) and the hereditarian (50% genetic-50% environmental) models of the causes of mean Black-White differences in cognitive ability are compared and contrasted across 10 categories of evidence: the worldwide distribution of test scores, g factor of mental ability, heritability, brain size and cognitive ability, transracial adoption, racial admixture, regression, related life-history traits, human origins research, and hypothesized environmental variables. The new evidence reviewed here points to some genetic component in Black-White differences in mean IQ. The implication for public policy is that the discrimination model (i.e., Black-White differences in socially valued outcomes will be equal barring discrimination) must be tempered by a distributional model (i.e., Black-White outcomes reflect underlying group characteristics).
... Summarized in Table 1 are the 50th percentile measures of stature, head length, and head breadth, separated by sex, taken directly from Jurgens et al. (1990). From these I derived cranial capacity (CC) using equations from Lee and Pearson (1901, p. 235) modified to subtract 11 mm for fat and skin around the skull (Rushton, 1993). ...
Recent studies have shown that even after correcting for body size, significant sex and race differences exist in brain size whether estimated from weight at autopsy, from endocranial volume, or from external head measurements. In this study, cranial capacities are calculated from external head measurements reported for 40 samples from a 1990 review of ergonomically important body measurements compiled by the International Labour Office in Geneva. The measurements had been gathered over the previous 30 years from tens of thousands of men and women aged 25 to 45 years. After adjusting for the effects of stature and race, 14 male samples averaged 1,362 cm3 and 14 female samples averaged 1,201 cm3. After adjusting for the effects of stature and sex, 6 East Asian samples averaged 1,308 cm3, 18 European samples averaged 1,297 cm3, and 4 African samples averaged 1,241 cm3.
... The results again confirm the racial differences. Rushton (1991 Rushton ( , 1992 Rushton ( , 1993 Rushton ( , 1994) and Rushton and Osborne (1995) carried out a series of studies estimating brain size this way from five large archival data sets. In the first of these studies, Rushton (1991) examined head size measures in 24 international military samples collated by the U.S. National Aeronautics and Space Administration and after adjusting for the effects of body height, weight, and surface area, found that the cranial capacity for East Asians was 1460 and for Europeans it was 1446 cm 3 . ...
A review of the world literature on brain size and IQ by Rushton [Rushton, J. P. (1995). Race, evolution, and behavior: a life history perspective. New Brunswick, NJ: Transaction] found that African-descended people (Blacks) average cranial capacities of 1267 cm3, European-descended people (Whites) 1347 cm3, and East Asian-descended people (East Asians) 1364 cm3. These brain size differences, containing millions of brain cells and hundreds of millions of synapses, were hypothesized to underlie the race differences on IQ tests, in which Blacks average an IQ of 85, Whites 100, and East Asians 106. The validity of the race differences in brain size, however, continues to be disputed. In the present study, the race differences in brain size are correlated with 37 musculoskeletal variables shown in standard evolutionary textbooks to change systematically with increments in brain size. The 37 variables include cranial traits (such as jaw size and shape, tooth size and shape, muscle attachment sites, and orbital bone indentations), and postcranial traits (such as pelvic width, thighbone curvature, and knee joint surface area). Across the three populations, the “ecological correlations” [Jensen, A. R. (1998). The g factor. Westport, CT: Praeger] between brain size and the 37 morphological traits averaged a remarkable r = .94; ρ = .94. If the races did not differ in brain size, these correlations could not have been found. It must be concluded that the race differences in average brain size are securely established. As such, brain size-related variables provide the most likely biological mediators of the race differences in intelligence.
... Cranial capacities were calculated for each person from the following two equations (Lee & Pearson, 1901): For males, where CC is cranial capacity and L and W are length and width in millimeters and 11 mm is subtracted for fat and skin around the skull. These equations give comparable results for different racial groups very similar to those derivable from Lee and Pearson's (1901) " panracial " equation, which also takes head height into account (see Rushton, 1993). The measurement descriptions are from Appendix B in Osborne (1980) and include muximum heud length (Column 21, the distance in millimeters between the glabella and the furthest point on the midline on the back of the head measured with a spreading caliper), maximum head breadth (Column 22, the greatest transverse distance in millimeters of the head, usually found over the parietal bone, measured with a spreading caliper), standing height (Column 24, inches in stocking feet), and weight (Column 25, pounds in street clothes without shoes). ...
Data from 236 pairs of twins (472 individuals) aged 13 to 17 years were used to examine genetic and environmental factors influencing cranial size, an indirect estimate of brain volume. Measures were taken of zygosity, head lenght, head breadth, age, sex, race, height, and weight for 187 males and 285 females, 222 Whites and 250 Blacks. Cranial size was estimated from head length and head breadth using standard equations. Group differences were found. Cranial capacity increased over age 13 to 17 from 1,233 cm3 to 1,279 cm3. After adjusting for the effects of age and body size, boys averaged 1,290 cm3 and girls 1,229 cm3, Whites averaged 1,269 cm3 and Blacks 1,251 cm3. Intraclass correlations were calculated and models fitted of proportionate genetic and environmental contributions to variance. Depending on particular corrections for body size, heritabilities for the sample as a whole ranged from 38% to 51% with 6% to 20% due to common environment and from 42% to 52% due to unique (nonshared) environmental factors, including error variance. The proportionate contributions did not vary systematically by sex and the seemingly higher range of heritabilities estimated for Whites than for Blacks (47% to 56% against 12% to 31%) and the lower range of common environment effects for Whites than for Blacks (28% to 32% against 42% to 46%) did not differ significantly. In conclusion, it is indicated that genetic factors are required to account for the phenotypic variance in cranial capacity and that further research is required on whether environmental factors exert more influence in Black populations than in White populations.
... However, given the very small within-race correlation of brain size and intelligence, and very small (trivial) Mongoloid-Caucasoid differences in IQ and in brain capacity, it would be irresponsible to draw any strong conclusions. More recently, Rushton (1993) has revised his work on sex differences in brain size and intelligence. There are many problems with this line of research (e.g., all the above correlations are for brain measurements statistically corrected for overall body size). ...
Psychology is distinguished from its brethren sciences of biology and sociology in that its main concern is with behavioral and mental processes of the individual (Zimbardo, 1992). Traditional study of personality and intelligence has focused on individual differences--searching for traits or relatively stable characteristics along which people differ (Eysenck & Eysenck, 1985; Howard, 1993). This line of research is based on the assumption that an improved scientific understanding of the nature of psychological functions can be achieved only by taking into account information about overall levels of performance and between-subjects variability and covariability. While the emphasis in individual differences research has been on multivariate procedures, experimental psychology has been almost exclusive in its focus on univariate designs. Multivariate research is closely linked to the development of psychological measuring instruments which are widely used in educational, industrial, and clinical settings. More recently, psychobiological explanations of personality and ability constructs have been sought (e.g., Zuckerman, 1991), opening the way for more sophisticated understanding of the neuropsychological and neuroendocrinological mechanisms underlying personality and ability traits. Hence, it is possible to claim that studies of intelligence and personality based on these combined approaches have made a more significant contribution to our social life in general than many other areas of psychological research (cf. Goff & Ackerman, 1992).
This chapter discusses the race differences in g and the Jensen Effect. It highlights that black-white IQ differences are more pronounced on highly g-loaded tests than on low g-loaded tests, g being the general factor of intelligence. Black-white differences on the g-factor occur regardless of whether testing is performed in the United States, in South Africa, or in the Netherlands. Further, it is found that the Lynn-Flynn effect may not be a Jensen Effect. The chapter also reviews the evidence for the default hypothesis-that genetic and cultural factors carry the same weight in causing black-white IQ differences, as they do in causing individual differences within each race. The chapter concludes by highlighting the robustness of the Spearman-Jensen hypothesis-that the more g-loaded a test is, the larger is the race difference-implying that a scientific understanding of the individual, group, or developmental differences depends on understanding the nature of g.
Reviews recent research which estimates racial differences in cranial capacity by measuring head dimensions of living persons. The authors describe errors in published reports and present findings that American Whites have greater head height than American Blacks, but that Blacks have greater head length and greater head circumference. Estimates of cranial capacity are determined by racial differences in head shape. Possible relations between head size and measured IQ are so small that they cannot possibly explain racial differences in IQ. The authors discuss why, despite this, "scientific" interest in race differences in cranial capacity persists. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Rushton (Personality and Individual Differences, 9, 1009–1024, 1988) hypothesized that racial group differences exist across a range of behaviors from intelligence to social organization. Such differences were then discussed within the context of an evolutionary continuum (Negroid < Caucasoid < Mongoloid). For example, his observations that blacks compared to whites are less intelligent, physically mature more rapidly, and are more aggressive and impulsive (less law abiding) were said to support the evolutionary hypothesis. Quantitative replication of the 100 studies included in Rushton's original ‘review and evolutionary analysis’ and a meta-analysis of 100 randomly selected studies infer that any behavioral differences which do exist between blacks, whites and Asian Americans for example, can be explained in toto by environmental differences which exist between them.
An estimate of someone's IQ is a potentially informative personal datum. This study examines the association between external skull measurements and IQ scores, and uses the resulting regression equation to provide an estimate of the IQ of King Robert I of Scotland (Robert Bruce, 1274–1329). Participants were 48 relatively healthy Caucasian men (age 71–76 years) resident in Scotland. Using magnetic resonance imaging data, intracranial volume estimated from external skull length and width correlated greater than .5 (p < .001) with measured intracranial area, which correlates very highly with brain volume. IQ scores estimated from the National Adult Reading Test (NART) correlated .56 (p < .001) with measured intracranial area, and .49 (p < .01) with estimated intracranial volume based on external skull width and length. The partial correlation coefficient of this latter association was .25 (p = .09) after adjustment for measured intracranial area. Thus, actual intracranial area accounts for about 74% of the variance shared by NART and estimated intracranial volume. A cast of the skull of Robert Bruce was measured and its intracranial volume estimated. A regression equation between IQ and estimated intracranial volume, based on data from the 48 subjects, estimated the IQ of Robert Bruce at about 128 (95% confidence interval 106 to ≫ 130), i.e. almost two standard deviations above the mean. NART scores show a ceiling effect, so this estimated IQ might be an underestimate. Robert Bruce's estimated high IQ is congruent with his military, political and other intellectual achievements.
Cranial capacity, brain weight and cerebral index are important measurements in the study of racial differences. Clinically, an analysis of cranial capacity and weight exposes another aspect of growth and development and permits critical evaluation of unusually large, small, or misshapen crania.
Brain weight and cerebral index were estimated in 772 normal 18-22-year-old (320 males, 452 females) Iranian people of different socioeconomic groups, using linear dimensions of the head (using Lee-Pearson's formula) measured with spreading caliper and auricular head spanner.
Cranial capacity, brain weight and cerebral index in males were 1343.45+/-102.37cm3 (mean+/-S.D.), 1390.47+/-105.95g, and 2.17+/-0.27% respectively. Cranial capacity, brain weight and cerebral index in females were 1163.02+/-115.76cm3, 1203.73+/-119.81g, and 2.25+/-0.31% respectively.
It was shown that neurocranial volume and weight of male is higher than female. Also, the results are different from previous studies in Western countries which may be a result of racial, topodemic, and socioeconomic variations. Finally, we propose the new "cerebral quotient" for anthropometric measurements.
Seven hundred and two (346 non-Asian, 356 Asian) undergraduate volunteers were assessed in a confidential laboratory setting on levels of interpersonal sexual behavior (e.g., petting, intercourse), intrapersonal sexual behavior (e.g., fantasy, masturbation), and sociosexual restrictiveness (e.g., lifetime number of partners, number of "one-night stands"). The purpose was to examine possible differences in sexual behavior between Asian and non-Asian Canadian university students and to determine the association between North American residency and the sexual behavior of Asians. The role of gender on sexual behavior both across and within ethnic groups was also examined. Statistical analyses revealed that Asian students were significantly more conservative than non-Asian students on all measures of interpersonal sexual behavior and sociosexual restrictiveness. Significant differences were also noted between Asian and non-Asian students on most measures of intrapersonal sexual behavior. With the exception of two fantasy items, length of residency in Canada was unrelated to interpersonal sexual behavior, intrapersonal sexual behavior, or sociosexual restrictiveness among Asians. Although gender differences were substantial for intrapersonal sexual behaviors such as fantasy and masturbation, no significant gender differences were found for measures of interpersonal sexual experience, with the exception of reported number of one-night stands.
The international literature on racial differences is reviewed, novel data are reported, and a distinct pattern is found. People of east Asian ancestry and people of African ancestry average at opposite ends of a continuum, with people of European ancestry averaging intermediately, albeit with much variability within each major race. The racial matrix emerges from measures taken of reproductive behavior, sex hormones, twinning rate, speed of physical maturation, personality, family stability, brain size, intelligence, law abidingness, and social organization. An evolutionary theory of human reproduction is proposed, familiar to biologists as the r-K scale of reproductive strategies. At one end of this scale are r-strategies, which emphasize high reproductive rates; at the other end are K-strategies, which emphasize high levels of parental investment. This scale is generally used to compare the life histories of widely disparate species, but here it is used to describe the immensely smaller variations among human races. It is hypothesized that, again on average, Mongoloid people are more K-selected than Caucasoids, who are more K-selected than Negroids. The r-K scale of reproductive strategies is also mapped on to human evolution. Genetic distances indicate that Africans emerged from the ancestral hominid line about 200,000 years ago, with an African/non-African split about 110,000 years ago, and a Caucasoid/Mongoloid split about 41,000 years ago. Such an ordering fits with and explains how and why the variables cluster.
Differential K Theory is proposed to help systematize individual and group differences in life histories, social behaviour and physiological functioning. K refers to one end of a continuum of reproductive strategies organisms can adopt, characterized by the production of very few offspring with a large investment of energy in each. At the opposite extreme is the r-strategy in which organisms produce a large number of offspring but invest little energy in any one. Between-species comparisons demonstrate that these reproductive strategies correlate with a variety of life history traits including: litter size, birth-spacing, parental care, infant mortality, developmental precocity, life span, intelligence, social organization and altruism. As a species, humans are at the K end of the continuum. Some people, however, are postulated to be more K than others. The more K a person is, the more likely he or she is to come from a smaller sized family, with a greater spacing of births, a lower incidence of DZ twinning, and more intensive parental care. Moreover, he or she will tend to be intelligent, altruistic, law-abiding, behaviourally restrained, maturationally delayed, lower in sex drive and longer lived. Thus diverse organismic characteristics, not otherwise relatable, are presumed to covary along the K dimension. Group differences are also hypothesized, such that, in terms of K: higher socio-economic > lower socio-economic; and Mongoloids > Caucasoids > Negroids.
The substance of this paper was a thesis for the London D. Sc. degree; it was shown to Professor Pearson, at whose suggestion considerable modifications were made, and a revision undertaken with a view to publication. In order to deal exactly with the problem of evolution in man it is necessary to obtain in the first place a quantitative appreciation of the size, variation, and correlation of the chief characters in man for a number of local races. Several studies of this kind have been already undertaken at University College. These fall into two classes, (i) those that deal with a variety of characters in one local race, and (ii) those which study the comparative value of the constants from a variety of races.
The brain size of hominids has increased approximately threefold during the evolution of the hominids fromAustralopithecus toHomo sapiens. It is proposed that the principal reason for this increase is that larger brains conferred greater intelligence, and greater
intelligence conferred a selection advantage.
A number of anthropologists have difficulty accepting this thesis because they believe that brain size is not associated with
intelligence in man. Evidence is reviewed, and new evidence from two studies is presented, to show that brain size as measured
by head size is positively correlated with intelligence as measured by intelligence tests. On two recent samples statistically
significant correlations of .21 and .30 were obtained between estimates of brain size and IQ. It is considered that brain
size is positively associated with intelligence in man and that this is the major reason for the increase in brain size of
the hominids during the last 3.2 million years.
This paper presents a theory of the intelligence of the Mongoloids consisting of three linked sub-theories. The first concerns the psychometric features of Mongoloid intelligence and proposes that Mongoloids are characterised by high general intelligence (Spearman's g), high visuospatial abilities and low verbal abilities. Mongoloid abilities also display slow maturation in infancy and early childhood. It is proposed that this pattern of abilities cannot be explained in environmental terms and should be regarded as substantially genetically programmed. The second sub-theory presents an evolutionary explanation for this pattern of abilities in Mongoloids, whereby it is proposed that the extreme cold of the ice ages acted as a selection pressure for increases in Spearman's g and the visuospatial abilities. The low verbal abilities and slow maturation rates are interpreted as by-products of these adaptations. The third sub-theory presents a neurological model for the Mongoloid brain in which it is proposed that cortex devoted to the visuospatial abilities was expanded at the expense of the cortex devoted to the verbal abilities. The implication that there exists a negative correlation between the visuospatial abilities and the verbal abilities is considered in the concluding part of the paper and shown to be correct.
It is widely believed that human brain size and intelligence are only weakly related to each other. Using magnetic resonance imaging, we show that larger brain size (corrected for body size) is associated with higher IQ in 40 college students equally divided by high versus average IQ, and by sex. These results suggest that differences in human brain size are relevant to explaining differences in intelligence test performance.
Racial differences exist on numerous heritable behaviour traits such that Caucasoids fall between Mongoloids and Negroids. Across samples, ages, and time periods, this pattern is observed on estimates made of brain size and intelligence (cranial capacity=1448, 1408, 1334 cm3., brain weight=1351, 1336, 1286 g; IQ scores=107, 100, 85); maturation rate (age to walk alone, age of puberty, age of death); personality and temperament (activity level, anxiety, sociability); sexual restraint (gamete production, intercourse frequency, size of genitalia); and social organization (marital stability, mental health, law abidingness). These observations may be explained in part in terms of gene-culture coevolutionarily based r/K reproductive strategies.
Cranial capacities (cm3) were calculated from external head measurements of male military personnel. For 24 international samples totalling 57,378 individuals collated in 1978, after adjusting for the effects of height, weight, and total body surface area, Mongoloids also average 1460 cm3 and Caucasoids averaged 1446 cm3. Another way of expressing the relationship is in terms of an “encephalization quotient” derived from the regression of cranial capacity on general body size, on which Mongoloids also averaged higher than Caucasoids.
Cain and Vanderwolf (Personality and Individual Differences 11, pp. 777–784, 1990) commit a Grand Type II Error in denying the relation between the variables juxtaposed in the title of this rejoinder. This reply (a) presents 20 studies showing a positive correlation between brain size and IQ, one of which used magnetic resonance imaging to scan the brain, (b) re-examines whether the races differ in brain size from data not previously presented including a reanalysis of a 1930 study using external head measurements and a 1984 study of endocranial volume and confirms that the ranking is Mongoloids &62; Caucasoids &62; Negroids, (c) suggests that when the appropriate brain-body allometric regressions are taken into account, sex differences in brain size disappear while race differences remain, and (d) explains the evolution of brain size, intelligence and race from a broad-based r / K life-history perspective.
The issue of whether human populations differ in brain size remains controversial. Cranial capacities were calculated from external head measurements reported for a stratified random sample of 6,325 U.S. Army personnel measured in 1988. After adjusting for the effects of stature and weight, and then, sex, rank, or race, the cranial capacity of men averaged 1,442 and women 1,332 cm3; that of officers averaged 1,393 and enlisted personnel 1,375 cm3; and that of Mongoloids averaged 1,416, Caucasoids 1,380, and Negroids 1,359 cm3.
Although it has long been known that women have absolutely smaller brains than men, it is widely thought that relative brain size, that is, brain size corrected for variation in body size, does not differ between the sexes. However, by reanalyzing a large data set on brain mass of black and white men and women, I show that, after correcting for body height or body surface area, men's brains are about 100 g heavier than female brains in both racial groups. This remarkable result leads to fascinating questions about the relation between brain size and intelligence, and about the evolution of brain size in humans.
A critique is presented of that portion of Rushton's theory on the role of race in heritable behavior that deals with race, brain size, and intelligence. The critique is based on an examination of all of the evidence that Rushton cited, as well as additional evidence. We find that the methods employed and data obtained by the cited studies are seriously flawed. Additional studies not cited by Rushton suggest a different ordering of brain size than that concluded by him. Strained logic, a failure to take into account alternative explanations, and contrary data seriously limit Rushton's effort. We conclude that there is no credible evidence to support Rushton's claimed relation between race, brain size, and intelligence.
The relationship between brain size and intelligence was investigated in two ways. Cranial capacity was measured in people with known IQs. A very small correlation was found between cranial capacity and intelligence; but this was shown to be the result of the confounding effects of height. A large series of brains was also investigated, data being obtained on occupation from the case notes. When the effects of body height and weight were controlled for, it was possible to demonstrate a statistically significant, but very slight, relation between brain size and occupational group.
There is increasing evidence that mammalian behavior patterns are basically female and that male patterns are induced by the action of the sex hormone testosterone on the brain of the newborn animal. Past studies supporting this view are discussed and new experimental evidence is presented. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Results from a synthesis of correlations between psychometric intelligence and two physical traits, head size and body size, are reported. Within-family studies are reviewed for evidence of pleiotropy, the effect of a single genetic factor on two traits. Studies are also reviewed to determine whether prenatal effects bias twin studies, leading to underestimates of genetic influence. An N-weighted mean partial correlation (controlling height) of .10 between intelligence and head size was found. Using a method developed by Van Valen (1974), the correlation of intelligence and brain size was estimated as .29 based on all the intelligence/head-size studies of adults and adolescents, and .44 based on studies measuring intelligence with IQ tests. The N-weighted mean partial correlations (controlling age) of intelligence and height were .18 for children and .22 for adults. The within-family studies indicated that pleiotropy may contribute to the correlation of intelligence with head size and to the correlation of intelligence with body size. Prenatal effects are not an important source of bias in twin studies or for heritability estimates based on them.
ATTENTION has recently been drawn1 to the indications that spatial ability-the ability to create, maintain and mentally transform a visual image1,2-has an X-linked recessive mode of inheritance in Caucasians1,3-8, with males having a proportionately greater facility1,9-12. At first glance, this result seems paradoxical in that such a presumably adaptive trait would not be expected to be transmitted on a recessive allele. If past selection pressures were exerted primarily on males, however in whom the spatial allele is co-dominant, the paradox would be resolved satisfactorily.
Analysis of 1,261 adult subjects, ages 25 to 80 years, showed that there is a positive relationship between the brain weight and the body dimensions. The brain weight, however, increases at a slower rate than the body dimensions. There is indication that only a small portion of the brain varies with variation in the body dimensions. Among parameters, the brain weight correlates best with the body surface area, followed by the body height and body weight. The brain weight is related to the body weight partly because it increases with increasing height. When adjusted to body dimensions, the brain weight is greater for white men than for black men and for white women than for black men. Our study also shows that the loss of brain mass proceeds at a slightly faster rate than loss of body mass.
The anthropometry of the American Negro Analysis of brain weight: I and II
- M J Herskovits
- K.-C Ho
- U Roessmann
- J V Straumtjord
- G Monroe
Herskovits, M. J. (1930). The anthropometry of the American Negro. New York: Columbia University Press. Ho. K.-C., Roessmann, U., Straumtjord, J. V. & Monroe, G. (1980). Analysis of brain weight: I and II. Archives of Pathology and Laboratory Medicine, 104, 635-645.
Retardufion in young children
- S H Broman
- P L Nichols
- P Shaughnessy
- W Kennedy
Broman, S. H., Nichols, P. L., Shaughnessy, P. & Kennedy, W. (1987). Retardufion in young children. Hillsdale, NJ: Erlbaum.
Physical correlates of human intelligence Biological approaches to the study of human intelligence
- A R Jensen
- S N Sinha
Jensen, A. R. & Sinha, S. N. (1993). Physical correlates of human intelligence. In Vernon, P. A. (Ed.), Biological approaches to the study of human intelligence. Norwood, NJ: Ablex.
Analysis of brain weight: I and II
- K C Ho
- U Roessmann
- J V Straumtjord
- G Monroe
Ho. K.-C., Roessmann,
U., Straumtjord,
J. V. & Monroe, G. (1980). Analysis of brain weight: I and II. Archives of
Pathology and Laboratory Medicine, 104, 635-645.
The anthropometry of the American Negro
- M J Herskovits
Herskovits,
M. J. (1930). The anthropometry of the American Negro. New York: Columbia University Press.
Race, brain size, and intelligence
- Rushton
Analysis of brain weight: I and II
- Ho
Biological factors and psychometric intelligence: A review
- Johnsom
Anthiopometric Source Book: Vol. 2. A handbook of anthropometric data
- United States National Aeronautics and Space Administration