Edited by Jennifer Reiling, Editorial Assistant.
Opinions regarding the weight of the brain being an index of intelligence
have fluctuated within wide limits. Before the days of cerebral localization
there were many physiologists who believed that an individual's intelligence
was directly proportionate to the total weight of the encephalon. A large
brain meant large mentality. As the encephalon began to be more closely investigated
and the post-mortem records were more carefully compared, it was discovered
that large brains were not always possessed by those who exhibited the highest
intelligence. In fact some of the greatest thinkers in the world were the
owners of brains much below the average in absolute weight and size. This
apparently upset the earlier physiologic dicta in regard to mind activity
being dependent on the physical brain. The discussion at once assumed two
aspects. Some physiologists frankly declared that mind was not solely a product
of brain function, but that it was an entity dependent for its manifestation
on the brain, but nevertheless quite separate and distinct from the latter.
Scalpel and alembic might analyze the brain, but they could do nothing to
explain the mind. These views characterized the metaphysical physiologists.
The materialistic physiologists, on the other hand, took the ground that the
mind was solely and in toto a product of brain activity,
and that accordingly it must follow that a large mind necessarily presupposes
a large brain. In attempting to harmonize their views with the apparently
contradictory observation that many of the most intelligent men were the possessors
of undersized brains, these physiologists were again divided into two camps,
as it were; some taking the ground that the cellular richness of the cortex,
including its convolutional development, was the real indicator of intelligence
irrespective of the total brain weight, while others maintained that the total
brain weight was the potential indicator though not necessarily the actual
one. The latter insisted that a large brain represented large capacity for
mentalization, and that the brain, like the muscles, was capable of development,
and the greater that development so much greater will be the resulting mentalization.
Its potentiality, according to these physiologists, rather than its manifested
activity is what is shown in its total weight.
BRAIN WEIGHT AS INDEX OF INTELLIGENCE.. JAMA. 1999;282(7):616F. doi:10.1001/jama.282.7.616