Academic journal article Canadian Journal of Experimental Psychology

Brain Size Matters: A Reply to Peters

Academic journal article Canadian Journal of Experimental Psychology

Brain Size Matters: A Reply to Peters

Article excerpt

Abstract Peters (1993) claimed that published research on brain size and IQ is flawed because it did not meet his list of "minimum conditions" that (a) subjects should be matched for height, weight and age, (b) analyses should be conducted separately within sex, (c) subjects should not vary in prenatal and nutritional history, (d) people with IQs appreciably below the population mean of 100 should not be studied, and (e) brain size measures should be done "blind". However, these "conditions" have either been met or are unnecessary and/or inappropriate. We show, contrary to Peters' claims, that (a) brain size is related to mental abilities, (b) brain size varies by sex and race, and (c) mental abilities vary by sex and race. Finally, we suggest that brain size constraints on behavioural complexity may be best understood from an evolutionary perspective.

Resume Peters (1993) a pretendu que la recherche publiee sur la correlation entre la dimension du cerveau et le QI n'etait pas valide car elle ne repondait pas aux exigences de sa liste de conditions minimales, a savoir (a) qu'il faudrait jumeler les sujets en fonction de leur taille, de leur poids et de leur a@ge; (b) que les analyses devraient se faire pour les gens d'un me@me sexe; (c) que les sujets devraient avoir des antecedents prenatals et de nutrition semblables; (d) qu'il faudrait exclure des resultats des tests les personnes dont le QI est substantiellement inferieur a la moyenne de 100 estimee pour la population generale; et, (e) que la mesure de la dimension du cerveau devrait se faire de maniere objective. Toutefois, ces conditions ont ete satisfaites ou sont inutiles et/ou inappropriees. Nous demon-trons, contrairement aux avances de Peters, que: (a) la dimension du cerveau a un rapport avec les facultes intellectuelles; (b) la dimension du cerveau varie selon la race et le sexe; et, (c) les facultes intellectuelles varient selon la race et le sexe. Enfin, nous suggerons que l'influence de la dimension du cerveau sur la complexite du comportement peut e@tre mieux comprise d'un point de vue tenant compte de I ' evolution.

In a reply to Lynn (1993) about brain size and IQ, Peters (1993) charged bias and questionable motives to dismiss relations first established over 100 years ago. Peters (1993) claimed that studies of brain size are confounded by systematic bias, including "racial bias", over and above normal measurement error. Peters (1993) also conjectured that uni-directional measurement errors may exist and so he dismissed Rushton's (1992) analyses showing race and sex differences in cranial capacity in 6,325 u.s. military personnel. Consequently, Peters claimed that such studies must be done "blind", i.e., the person doing the measurement should not know the race of the subject being measured.

Peters did not note, although it was made clear in Rushton's (1992) paper, that (1) Rushton neither made the measurements nor knew who did, and (2) measurements were made to determine proper helmet sizes not brain sizes (i.e., they were done "blind", as the measurers were unaware of the use that Rushton would make of their data). The East Asian/European/African differences that Rushton (1992) found in cranial capacity (cm'Symbol not transcribed'3) using external head measurements are similar to those found by Beals, Smith, and Dodd (1984) who estimated cm'Symbol not transcribed'3 from endocranial volume, and by Ho, Roessmann, Straumfjord, and Monroe (1980) who weighed brain mass (grams) at autopsy. Does Peters believe that Ho et al. "leaned" on their scales, when weighing brains of European-Americans, by just enough to produce the same difference caused by "extra snug" measurements supposedly made by those measuring heads of African-Americans? Regardless, it is implausible that the "racial bias" alleged by Peters would also produce findings that East Asians have relatively larger brains than do Europeans.

Allometric and nutritional factors

Peters (1993) misstates when and why it is appropriate to correct for variation in body size (e. …

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