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The size of the Negroid brain is significantly lower in volume than the Mongoloid or Caucasoid brain. The size of its frontal lobes are small, uncomplex, and the brain as a whole shows an unimpressive, moderate degree of fissuring (Lynn, 2006a, pp. 210-211; Rushton, 2000a, pp. 130, 133).
Converting brain volume into the number of neurons, Mongoloids average more than half a billion more neurons than Negroids (Rushton, 2000a, p. 133; Broom, 1918, p. 63-79; Howells, 1948, p. 118; Galloway, 2005, pp 31-47). The East Asians (Chinese, Koreans, and Japanese) have the highest ratio of brain to body mass, but the record for brain size goes to Russian writer Ivan Turgenev, at 2012 gms (Corballis, 1991, p. 66). The heritability of brain size is about 0.9 (Lynn, 2006a, p. 67).
The ridges ("gyri") between the groves ("sulci") at the surface of the brain greatly increase the surface area of the cerebral cortex, the outer layer of the cerebrum. Since the cerebral cortex processes information, increased brain fissures increases the percentage of the brain that is cerebral cortex and should increase intelligence without increasing the volume of the brain, although this is difficult to establish quantitatively (Baker, 1974, p. 432). Africans and some retarded people have fewer convolutions ("fissures") in the cerebral cortex of their brains, where abstract thought is performed (Broca, 1858, cited by Rushton, 2000a, p. 106).
There are many other physical properties of the brain that are also associated with greater intelligence. More intelligent brains show faster nerve conduction, less glucose utilization in positron emission tomography [PET scans], faster reaction times, faster inspection times, faster speeds in general, greater circumference and volume, smaller standard deviation in reaction times, greater variability in EEG [electroencephalogram] measures, shorter white matter T2 relaxation times, and higher gray-white matter contrast with magnetic resonance imaging [MRI] (Miller, 1994d). The thickness of the three outer layers (the supragranular layer) of the cerebral cortex (the six outer layers), increases from lower animals to man (Corballis, 1991, p. 67). The supragranular layer is 15% thinner in blacks than in whites (Vint, 1934). The nerves in blacks are reported to be larger (Burmeister, 1853).
The prefrontal area typically constitutes 29% of a man's brain (Herrick, 1956, p. 385). The human neocortex is over three times as large as expected for a primate matched for body size (Passingham, 1982). Compared to Eurasians, in Africans the back of the brain is more developed and the front less developed (Broca, 1858, cited by Rushton, 2000a, p. 106; Bean, 1906; Levin, 1997, p. 105). This is noticeable in the more sloping forehead of Africans and the length of their skull. Vision is processed in the back of the brain, hearing at the side, and planning and abstract thought at the front. Thus, a brain that is more devoted to one of these functions than to others will have a greater mass of brain tissue in that area and the skull shape will be expanded in that area.
A frontal lobotomy, which removes the anterior frontal area of the brain, leaves a person conscious and seemingly normal, but unable to plan and take initiative (Penfield, 1957, p. 226). That is why Africans have been compared to lobotomized Europeans (Simpson, 2003, p. 705).
Racial differences in the relative sizes of different areas of the brain are suggested by the way smoking affects the races. Compared to white smokers, American black smokers absorb 30% more nicotine per cigarette and take longer to rid their bodies of the drug (Dr. Nora Volkow, "News Release," National Institute on Drug Abuse, Jan., 20, 2006). Numerous studies have demonstrated significant racial differences in the metabolism of tobacco-related products (Wilson, S.E., "Study Examines Racial Differences Among Children To Environmental Tobacco Smoke Exposure Cincinnati Children's Center for Environmental Health," Mar. 15, 2005). Since different neurotransmitters in the brain take up nicotine at different rates, this implies that blacks and whites have significant differences in the relative sizes of different areas of the brain. African Americans have much lower slow wave brain activity during sleep than do Caucasians, which also suggests structural differences in the brain ("Slow Wave Activity During Sleep Is Lower In African-Americans Than Caucasians," Science Daily, June 13, 2007).
Thus, in our journey to become human, our brain not only increased in size, but certain portions, such as the frontal lobes, the cerebral cortex, and its supragranular layer, increased disproportionately. Also, the sulci and gyri increased and deepened. Other parts, such as the olfactory bulb, devoted to smell, have increased less than proportionately. These changes were greater in Eurasians than in Africans.
Researchers have found that certain regions of the brain responsible for intelligence are highly heritable, including language areas (such Broca's area and Wernicke's area) and the frontal region (which plays a large role in abstract reasoning) (Thompson, 2001).
Converting brain volume into the number of neurons, Mongoloids average more than half a billion more neurons than Negroids (Rushton, 2000a, p. 133; Broom, 1918, p. 63-79; Howells, 1948, p. 118; Galloway, 2005, pp 31-47). The East Asians (Chinese, Koreans, and Japanese) have the highest ratio of brain to body mass, but the record for brain size goes to Russian writer Ivan Turgenev, at 2012 gms (Corballis, 1991, p. 66). The heritability of brain size is about 0.9 (Lynn, 2006a, p. 67).
The ridges ("gyri") between the groves ("sulci") at the surface of the brain greatly increase the surface area of the cerebral cortex, the outer layer of the cerebrum. Since the cerebral cortex processes information, increased brain fissures increases the percentage of the brain that is cerebral cortex and should increase intelligence without increasing the volume of the brain, although this is difficult to establish quantitatively (Baker, 1974, p. 432). Africans and some retarded people have fewer convolutions ("fissures") in the cerebral cortex of their brains, where abstract thought is performed (Broca, 1858, cited by Rushton, 2000a, p. 106).
There are many other physical properties of the brain that are also associated with greater intelligence. More intelligent brains show faster nerve conduction, less glucose utilization in positron emission tomography [PET scans], faster reaction times, faster inspection times, faster speeds in general, greater circumference and volume, smaller standard deviation in reaction times, greater variability in EEG [electroencephalogram] measures, shorter white matter T2 relaxation times, and higher gray-white matter contrast with magnetic resonance imaging [MRI] (Miller, 1994d). The thickness of the three outer layers (the supragranular layer) of the cerebral cortex (the six outer layers), increases from lower animals to man (Corballis, 1991, p. 67). The supragranular layer is 15% thinner in blacks than in whites (Vint, 1934). The nerves in blacks are reported to be larger (Burmeister, 1853).
The prefrontal area typically constitutes 29% of a man's brain (Herrick, 1956, p. 385). The human neocortex is over three times as large as expected for a primate matched for body size (Passingham, 1982). Compared to Eurasians, in Africans the back of the brain is more developed and the front less developed (Broca, 1858, cited by Rushton, 2000a, p. 106; Bean, 1906; Levin, 1997, p. 105). This is noticeable in the more sloping forehead of Africans and the length of their skull. Vision is processed in the back of the brain, hearing at the side, and planning and abstract thought at the front. Thus, a brain that is more devoted to one of these functions than to others will have a greater mass of brain tissue in that area and the skull shape will be expanded in that area.
A frontal lobotomy, which removes the anterior frontal area of the brain, leaves a person conscious and seemingly normal, but unable to plan and take initiative (Penfield, 1957, p. 226). That is why Africans have been compared to lobotomized Europeans (Simpson, 2003, p. 705).
Racial differences in the relative sizes of different areas of the brain are suggested by the way smoking affects the races. Compared to white smokers, American black smokers absorb 30% more nicotine per cigarette and take longer to rid their bodies of the drug (Dr. Nora Volkow, "News Release," National Institute on Drug Abuse, Jan., 20, 2006). Numerous studies have demonstrated significant racial differences in the metabolism of tobacco-related products (Wilson, S.E., "Study Examines Racial Differences Among Children To Environmental Tobacco Smoke Exposure Cincinnati Children's Center for Environmental Health," Mar. 15, 2005). Since different neurotransmitters in the brain take up nicotine at different rates, this implies that blacks and whites have significant differences in the relative sizes of different areas of the brain. African Americans have much lower slow wave brain activity during sleep than do Caucasians, which also suggests structural differences in the brain ("Slow Wave Activity During Sleep Is Lower In African-Americans Than Caucasians," Science Daily, June 13, 2007).
Thus, in our journey to become human, our brain not only increased in size, but certain portions, such as the frontal lobes, the cerebral cortex, and its supragranular layer, increased disproportionately. Also, the sulci and gyri increased and deepened. Other parts, such as the olfactory bulb, devoted to smell, have increased less than proportionately. These changes were greater in Eurasians than in Africans.
Researchers have found that certain regions of the brain responsible for intelligence are highly heritable, including language areas (such Broca's area and Wernicke's area) and the frontal region (which plays a large role in abstract reasoning) (Thompson, 2001).
