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Many studies report that IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[2] The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar),[3] but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families.[4] Some studies have found racial differences in brain size.[5]

Others interpret these studies as having found no racially-based difference, arguing instead the the variation should be described in terms of geography.[6] Perhaps the largest single study, by Beals et al. 1984 which analyzed more than 20,000 skulls from 122 ethnically distinguishable populations, found that brain size varied with distance from the equator (r=.62). Lieberman 2001 explains "...the relationship between latitude and cranial size is an example of Bergmann's principle that crania are more spherical in cold climates because mass increases relative to surface area to conserve core temperatures...Beals, Smith, and Dodd emphasize that this relationship is independent of "race."".[7] The biogeographical variation in brain size is widely described as an evolutionary adaptation to climate. Building on the findings of Beals et al., Templer and Arikawa 2006 reported that mean national IQ is correlated with skin color and climate.

Cranial vault size and shape have changed greatly during the last 150 years in the US.[citation needed] These changes must occur by early childhood because of the early development of the vault.[citation needed] The explanation for these changes may be related to the Flynn effect.[8]

A meta-analysis found that reaction times correlates with IQ by about .30 to .50.[9] Average racial differences have been found on tests of response time.[10] Reaction time also correlates with brain volume at approximately .4.[11]

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There are several hotly debated studies which have concluded that there are race-based differences in brain size. These studies are criticized as having found no genetically racially-based difference, with critics arguing instead the the variation correlates much better in terms of geography and environment.[12][13] Perhaps the largest single study, by Beals et al. 1984 which analyzed more than 20,00 skulls from around the world, found that brain size varied with latitude of biogeographic ancestry. Lieberman (2001) explains "...the relationship between latitude and cranial size is an example of Bergmann’s principle that crania are more spherical in cold climates because mass increases relative to surface area to conserve core temperatures...Beals, Smith, and Dodd emphasize that this relationship is independent of "race."".[14] The biogeographical variation in brain size is widely described as an adaptation to climate.

Cranial vault size and shape have changed greatly during the last 150 years in the US.[citation needed] These changes must occur by early childhood because of the early development of the vault.[citation needed] The explanation for these changes may be related to the Flynn effect.[15]

Several studies report that IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[16] The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar),[17] but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families.[18]

A meta-analysis found that reaction times correlates with IQ by about .30 to .50.[19] Average racial differences have been found on tests of response time, although it is also argued that some of these differences can be explained by cultural phenomena.[20]

It is argued by some scientists that the combination of these correlations, of race to brain size, of brain size to reaction time, and of reaction time to IQ establishes a correlation between race and IQ. This conclusion is strongly objected to by other scientists, both on the basis of the initial correlation asserted between race and brain size, and the progressively weak correlation as the studies are combined.[13]

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Many studies report that IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[21] The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar),[22] but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families.[23] Some studies have found racial differences in brain size.[24]

Others interpret these studies as having found no racially-based difference, arguing instead the the variation should be described in terms of geography.[25] Perhaps the largest single study, by Beals et al. 1984 which analyzed more than 20,000 skulls from around the world, found that brain size varied with latitude of biogeographic ancestry (r=.62). Lieberman 2001 explains "...the relationship between latitude and cranial size is an example of Bergmann's principle that crania are more spherical in cold climates because mass increases relative to surface area to conserve core temperatures...Beals, Smith, and Dodd emphasize that this relationship is independent of "race."".[26] The biogeographical variation in brain size is widely described as an evolutionary adaptation to climate.

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.[27]

A meta-analysis found that reaction times correlates with IQ by about .30 to .50.[28] Average racial differences have been found on tests of response time.[29] Reaction time also correlates with brain volume at approximately .4.[30]

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Many studies report that IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[31] The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar),[32] but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families.[33] Some studies have found racial differences in brain size,[34] while others found no racially-based difference.[35] Perhaps the largest single study, by Beals et al. 1984 which analyzed more than 20,00 skulls from around the world, found that brain size varied with latitude of biogeographic ancestry. Lieberman (2001) explains "...the relationship between latitude and cranial size is an example of Bergmann’s principle that crania are more spherical in cold climates because mass increases relative to surface area to conserve core temperatures...Beals, Smith, and Dodd emphasize that this relationship is independent of “race.”".[36] The biogeographical variation in brain size is widely described as an adaptation to climate. 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.[37]

A meta-analysis found that reaction times correlates with IQ by about .30 to .50.[38] Average racial differences have been found on tests of response time.[39]


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Many studies report that IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[40] The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar)[41], but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families.[42] Some studies have found racial differences in brain size[43]. A large study by Beals et al. 1984 found that the brain size of indigenous populations varied with latitude. Lieberman and others, who do not believe that human variation should be described in terms of races, argue that the clinal view of brain size variation is superior to a racial description.[44]. The biogeographical variation in brain size is widely described as an adapatation to climate. 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.[45]

A meta-analysis found that reaction times correlates with IQ by about .30 to .50.[46] Average racial differences have been found on tests of response time.[47]


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Many studies report that IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[48] The correlation was also found in some studies to hold true within families (where environmental factors can be considered to be similar)[49], but in one study of 36 sibling pairs essentially zero correlation between brain size and IQ was found when comparing within families.[50] Some studies have found racial differences in brain size[51]. A large study by Beals et al. 1984 found that the brain size varied with latitude, pointing out that the racial correlation was much lower than correlation with climate. [52]. The biogeographical variation in brain size is widely described as an adaptation to climate (Lieberman, 2001). 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.[53]

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IQ has a moderate correlation with various measures of brain size and performance on elementary tests of response time.[1] For example, a 2005 meta-analysis found that brain size correlates with IQ by a factor of approximately .40 among adults.[54] Reaction times correlate with IQ by about .30 to .50.[55] Studies have shown racial differences in both brain size[56] and tests of response time.[57] 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.[58]

  1. ^ a b c d e f g Neisser et al. 1996
  2. ^ McDaniel 2005; see also Bartley et al. 1997; Pennington et al. 2000; Posthuma et al. 2002; Rushton and Osborne 1995; Thompson et al. 2001
  3. ^ Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994
  4. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=18335
  5. ^ see Neisser 1997, p. 80
  6. ^ see Lieberman 2001 [1], Table 1
  7. ^ see http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Lieberman2001CA.pdf especially references to the work of Beals et al, 1984
  8. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  9. ^ Grudnik and Kranzler 2001
  10. ^ see Race and intelligence (Average gaps among races)#Reaction time
  11. ^ Wickett et al. 2000
  12. ^ Neisser 1997
  13. ^ a b Cite error: The named reference lieberman was invoked but never defined (see the help page).
  14. ^ see http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Lieberman2001CA.pdf especially references to the work of Beals et al, 1984
  15. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  16. ^ McDaniel 2005; see also Bartley et al. 1997; Pennington et al. 2000; Posthuma et al. 2002; Rushton and Osborne 1995; Thompson et al. 2001
  17. ^ Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994
  18. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=18335
  19. ^ Grudnik and Kranzler 2001
  20. ^ see Race and intelligence (Average gaps among races)#Reaction time
  21. ^ McDaniel 2005; see also Bartley et al. 1997; Pennington et al. 2000; Posthuma et al. 2002; Rushton and Osborne 1995; Thompson et al. 2001
  22. ^ Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994
  23. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=18335
  24. ^ see Neisser 1997, p. 80
  25. ^ see Lieberman 2001 [2], Table 1
  26. ^ see http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Lieberman2001CA.pdf especially references to the work of Beals et al, 1984
  27. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  28. ^ Grudnik and Kranzler 2001
  29. ^ see Race and intelligence (Average gaps among races)#Reaction time
  30. ^ Wickett et al. 2000
  31. ^ McDaniel 2005; see also Bartley et al. 1997; Pennington et al. 2000; Posthuma et al. 2002; Rushton and Osborne 1995; Thompson et al. 2001
  32. ^ Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994
  33. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=18335
  34. ^ see Neisser 1997, p. 80
  35. ^ see Lieberman 2001 [3], Table 1
  36. ^ see http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Lieberman2001CA.pdf especially references to the work of Beals et al, 1984
  37. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  38. ^ Grudnik and Kranzler 2001
  39. ^ see Race and intelligence (Average gaps among races)#Reaction time
  40. ^ McDaniel 2005; see also Bartley et al. 1997; Pennington et al. 2000; Posthuma et al. 2002; Rushton and Osborne 1995; Thompson et al. 2001
  41. ^ Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994
  42. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=18335
  43. ^ see Neisser 1997, p. 80
  44. ^ see http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Lieberman2001CA.pdf especially references to the work of Beals et al, 1984
  45. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  46. ^ Grudnik and Kranzler 2001
  47. ^ see Race and intelligence (Average gaps among races)#Reaction time
  48. ^ McDaniel 2005; see also Bartley et al. 1997; Pennington et al. 2000; Posthuma et al. 2002; Rushton and Osborne 1995; Thompson et al. 2001
  49. ^ Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994
  50. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=18335
  51. ^ see Neisser 1997, p. 80
  52. ^ see http://www.ssc.uwo.ca/psychology/faculty/rushtonpdfs/Lieberman2001CA.pdf especially references to the work of Beals et al, 1984
  53. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
  54. ^ McDaniel 2005
  55. ^ Grudnick and Kranzler 2001
  56. ^ see Neisser 1997, p. 80 for a consensus statement
  57. ^ see Race and intelligence (Average gaps among races)#Reaction time
  58. ^ Gravlee et al. 2003a, Gravlee et al. 2003b; Jantz and Jantz 2000, Jantz 2001
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