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作者：Anonymous 在 罕见奇谈 发贴, 来自 http://www.hjclub.org
Race differences
Rushton (1995) reviewed 100 years of scientific literature and found that across a triangulation of procedures, brains of East-Asians and their descendants average about 17 cm3 (1 in3) larger than those of Europeans and their descendents whose brains average about 80 cm3 (5 in3) larger than those of Africans and their descendents. Although critics can pick outliers to show counter-examples and suggest opposite trends (as could critics of a statement that men are, on average, taller than women) the aggregated data are clear (see Rushton, 1995, for full discussion of alleged counter examples).
Consider the following statistically significant comparisons. Using brain mass at autopsy, Ho et al. (1980) summarized data for 1,261 adults (see above) and reported a sex-combined difference between 811 European- Americans with a mean of 1,323 g (sd = 146) and 450 African-Americans with a mean of 1,223 g (sd = 144). Using endocranial volume, Beals et al. (1984, page 307, Table 5) analyzed 20,000 crania and found sex-combined brain cases differed by continental area. Excluding Caucasoid areas of Asia (e.g., India) and Africa (e.g., Egypt), 19 East Asian populations averaged 1,415 cm3 (sd = 51), 10 European groups averaged 1,362 cm3 (sd = 35) and 9 African groups averaged 1,268 cm3 (sd = 85). Using external head measure- ments, Rushton (1992) found, in a stratified random sample of 6,325 U.S. Army personnel, measured in 1988 to determine head size for fitting helmets, Asian-Americans, European-Americans, and African-Americans averaged 1,416, 1,380, and 1,359 cm3, respectively (see also, Rushton, 1994).
Globally, racial differences in brain size parallel those found in measured intelligence. Europeans in North America, Europe and Australasia have mean IQs of around 100. For East Asians, measured in North America and in Pacific Rim countries, means range from 101 to 111. Africans living south of the Sahara, African-Americans and African-Caribbeans (including those living in Britain), have mean IQs of from 70 to 90 (Lynn, 1991). Elementary speed of information processing in 9- to 12-year-olds, in which children decide which of several lights stands out from others, show that racial differences in mental ability are pervasive. All children can perform the tasks in less than 1 s, but more intelligent children, as measured by traditional IQ tests, perform the tasks faster than do less intelligent children. Japanese and Hong Kong children have faster decision times (controlling for movement time) than do British and Irish children who have faster decision time than South African Black and African-American children (Jensen, 1993; Jensen & Whang, 1993; Lynn, 1991).
Evolutionary considerations
Metabolically, the human brain is an expensive organ. Representing only 2% of body mass, the brain uses about 5% of basal metabolic rate in rats, cats, and dogs, about 10% in rhesus monkeys and other primates, and about 20% in humans. Thus, from an adaptationist perspective, unless large brains substantially contributed to evolutionary fitness (defined as increased survival of genes through successive generations), they would not have evolved.
Paradoxically, Peters (1993) cited Haug (1987) to refute speculations about the significance of differences in brain size across individuals, sex, or race , even though Haug (1987, p.135) reported a correlation of r = 0.479 (n = 81, p < .001) between number of cortical neurons and brain size including both men and women in the sample. Haug's analysis showed that a person with a brain size of 1,400 cm3 has, on average, 600 million fewer cortical neurons than an individual with a brain size of 1,500 cm3. The difference between the low end of normal (1,000 cm3) and the high end (1,700 cm3) equates to 4.200 billion neurons (a difference of 27% more neurons for a 41% increase in brain size).
Haug noted that most female data points lay above the regression line (i.e., women average more neurons for a given brain size than do men). This suggests that women’s brains are differently organized than are men’s, and so causes and results of race differences in brain size may be different from those of sex differences. Kolakowski and Malina (1974) hypothesized that differing roles of men and women during human evolution produced a sexual dichotomy in abilities. Men roamed from the home base to hunt, which would select for targeting ability and navigational skills; women were relatively sedentary. Ankney (1992, 1995) expanded on this hypothesis to argue that selection for such abilities also selected for relatively larger brains in men and that it may require more brain tissue to process spatial information.
Rushton (1995) provided an evolutionary hypothesis for why East Asians have the largest brains. The currently accepted view of human origins posits a beginning in Africa some 200,000 years ago, an African/non-African split about 110,000 years ago, and a European/East Asian split about 40,000 years ago (Stringer & Andrews, 1988). Evolutionary selection pressures were different in the hot savanna where Africans evolved than in the cold arctic where East Asians evolved. According to Rushton (1995), the further north the populations migrated, out of Africa, the more they encountered cognitively demanding problems of gathering and storing food, gaining shelter, making clothes, and raising children during prolonged winters. As the original African populations evolved into Europeans and East Asians, they did so in the direction of larger brains, greater intelligence, slower rates of maturation, and other traits that differentiate these populations.
Conclusion
The evidence is overwhelming that there are racial and sexual differences in brain size, that there are racial differences in general IQ, that there are sexual differences in verbal versus performance IQ, and that differences in mental abilities are related to differences in brain size. Peters cannot simply deny this evidence. Thus, important research questions include (1) what is responsible for the group differences, i.e., are they genetically and/or environmentally caused?, (2) does the brain size/IQ correlation indicate cause and effect ?, and (3) is there bidirectional causality such that the greater learning ability of high IQ children feeds back to produce even larger brain size?
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作者：Anonymous 在 罕见奇谈 发贴, 来自 http://www.hjclub.org |
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Race differences
