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Individual differences |
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Human skulls can be classified into three main categories based on cephalic index:
- dolichocephalic: long and thin
- brachycephalic: short and broad
- mesocephalic: intermediate length and breadth
There exist several indices other than the cephalic index that are meant to measure certain attributes of the head, as well.
Scientific research throughout history Edit
In 1764, Louis-Jean-Marie Daubenton published a noteworthy contribution to craniometry: Mémoire sur les differences de la situation du grand trou occipital dans l’homme et dans les animaux (which translates as Memoir on the Different Positions of the Occipital foramen in Man and Animals). Six years later, Pieter Camper, distinguished both as an artist and as an anatomist, published some lectures containing an account of his craniometrical methods, and these may be fairly claimed as having laid the foundation of all subsequent work. That work has been described above as anthropological, but as the studies thus defined are very varied in extent, it is necessary to consider the subdivisions into which they naturally fall.
In the first place, (omitting further reference to the artists), it has been explained that the measurements were first made with a view to elucidating the comparison of the skulls of men with those of other animals. This wide comparison constitutes the first subdivision of craniometric studies. It is further remarkable that among the first measurements employed angular determinations occur, and indeed the name of Camper is chiefly perpetuated in anthropological literature by the facial angle invented by that artist-anatomist.
Camper's work followed the lines of 18th century racial theories, where his measurements of facial angle were used to liken the skulls of non-Europeans to those of apes.
In the 19th century the names of notable contributors to the literature of craniometry quickly increased in number. While it is impossible to analyse each contribution, or even record a complete list of the names of the authors, it must be added that for the purposes of far-reaching comparisons of humans to other animals, craniometric methods were used by Paul Broca in France and by T. H. Huxley in England.
Broca and Huxley cultivated similar comparative racial fields of research, but to these names that of Anders Retzius of Stockholm must be added. The chief claim of Retzius to distinction rests on the merits of his system of comparing various dimensions of the skull, and of a classification based on such comparisons.
The misuse of data obtained from craniometry has been compared to phrenology as a pseudoscience. The apparent scientific support of craniometric theories for racism was used to the support the racist ideologies, and ultimately genocidal policies, of the Nazi party. The uses that racist ideologues and even reputable scientists made of craniometric measurements and conclusions have been thoroughly discussed by Stephen Jay Gould in The Mismeasure of Man (1981).
However, brain volume data and other craniometric data is used in mainstream science to compare modern-day animal species, and to analyze the evolution of the human species in archeology.
Racial difference in brain size Edit
In his 1839 Crania Americana, anthropologist Samuel George Morton reported that the mean cranial capacity of the skulls of Whites was 87 in³ (1,425 cm³), while that of Blacks was 78 in³ (1,278 cm³). Based on the measurement of 144 skulls of Native Americans, he reported a figure of 82 in³ (1,344 cm³).
Morton's work has been criticized by Stephen Jay Gould, who alleged in his 1981 book The Mismeasure of Man that Morton was guilty of fudging data and "overpacking" the skulls with filler. Gould writes that the differences are "trivial", but J. Philippe Rushton (1996) responds that a difference of only 1 cubic inch (16 cm³) equates to millions of neurons.
In 1988, J. S. Michael remeasured a random sample of Morton's skulls and concluded that Morton had made very few errors. J. Philippe Rushton (1989) additionally reanalyzed Gould's retabulation, concluding that Morton had shown a pattern of decreasing brain size proceeding from East Asians, Europeans, and Africans.
In 1873, Paul Broca found the same pattern by weighing brains at autopsy. Other historical studies showing a Black-White difference in brain size include Bean (1906), Mall, (1909), Pearl, (1934) and Vint (1934).
In his controversial 1995 work Race, Evolution, and Behavior, J. Philippe Rushton reported an average endocranial volume of 1,415 cm³ for "Orientals" [sic] , 1,362 for Whites, and 1,268 for Blacks. When adjusted for average body size, the differences become more pronounced; i.e., the encephalization quotients (EQ) display greater differences than do absolute brain sizes (Jerisen, 1973, 2000; Rushton, 1991). Rushton (1991) found an EQ of 7.26 for East Asians as compared to 6.76 for Caucasians. Differences in brain size between Asians and Europeans sometimes do not appear until adjusted for body size (Rushton, 1997). In some cases Europeans averaged higher absolute brain sizes than East Asians but lower relative brain sizes when adjusted for body size (Rushton, 1994).
Other studies that have shown similar patterns in average brain size include Ho et al. (1980), who measured 1,261 brains at autopsy, and Beals et al. (1984), who measured approximately 20,000 skulls, finding the same East Asian → European → African pattern. Other studies have shown the same pattern in average head size, including Rushton (1992), Rushton (1994), and the National Collaborative Perinatal Project  (described by Broman, Nichols, Shaugnessy, & Kennedy, 1987) which collected anthropometric data, including head measurements and IQ, on approximately 35,000 children from 1959 to 1974 (although the study began with over 50,000 subjects, some attrition occurred as with many longitudinal studies). Analyses of the data found the East Asian → White → Black pattern in head size and IQ at 4 months, 1 year, and 7 years of age.
East Asian brains have greater width and breadth (i.e., are more brachycephalic) and are more spherically shaped than those of Europeans, which are more so than those of Africans. Africans tend to have longer and narrower (more dolichocephalic) brains (Beals et al., 1984; McShane, 1983; Rushton & Ankney, 2000). Beals et al. proposed that the longer and narrower African brain evolved for better heat dissipation in a warmer climate, while East Asians and Europeans evolved comparatively shorter and wider brains for thermoregulatory purposes in a cooler climate. Rushton & Ankney (2000, pp. 612-613) question the thermoregulatory hypothesis, instead positing that brachycephalization and sphericalization allow for greater brain size. At the same time, Rushton and Ankney believe it is possible that the need to thermoregulate in Africa may have selected against increasing brain size.
Rushton and Ankney (2000) found a pattern of descending prognathism, glabella size, postorbital constriction, and temporal fossae in African, European, and East Asian skulls and propose that these structures shrank over the course of evolution to allow greater brain size.
Rushton has been accused by other researchers of misrepresenting the data. When they have reanalyzed the data, Zack Cernovsky et al. argue that many of Rushton's claims are incorrect.
Cranial vault size and shape have changed greatly during the last 150 years in the US. These changes must occur by early childhood because of the early development of the vault. The explanation for these changes may be related to the Flynn effect.
See also Edit
- This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.ca:Craniometria
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