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Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 9, 4932-4937, April
25, 2000 Brain size does not predict general cognitive ability
within families http://www.pnas.org/cgi/content/abstract/97/9/4932
P. Thomas Schoenemann*,, Thomas F. Budinger, Vincent M. Sarich§,
and William S.-Y. Wang * Department of Anthropology, University
of Pennsylvania, Philadelphia, PA 19104-6398; Center for Functional
Imaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
§ Department of Anthropology, University of California, Berkeley,
CA 94720; and Department of Electronic Engineering, City University
of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, and Department
of Linguistics, University of California, Berkeley, CA 94720
Hominid brain size increased dramatically in the face of apparently
severe associated evolutionary costs. This suggests that increasing
brain size must have provided some sort of counterbalancing adaptive
benefit. Several recent studies using magnetic resonance imaging
(MRI) have indicated that a substantial correlation (mean r =
0.4) exists between brain size and general cognitive performance,
consistent with the hypothesis that the payoff for increasing
brain size was greater general cognitive ability. However, these
studies confound between-family environmental influences with
direct genetic/biological influences. To address this problem,
within-family (WF) sibling differences for several neuroanatomical
measures were correlated to WF scores on a diverse battery of
cognitive tests in a sample of 36 sibling pairs. WF correlations
between neuroanatomy and general cognitive ability were essentially
zero, although moderate correlations were found between prefrontal
volumes and the Stroop test (known to involve prefrontal cortex).
These findings suggest that nongenetic influences play a role
in brain volume/cognitive ability associations. Actual direct
genetic/biological associations may be quite small, and yet still
may be strong enough to account for hominid brain evolution.
To whom reprint requests should be addressed at: Department of
Anthropology, 325 University Museum, University of Pennsylvania,
33rd and Spruce Streets, Philadelphia, PA 19104-6398.
E-mail: ptschoen@sas.upenn.edu |
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