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The Neuron- Up Close and Personal

The Question of Intelligence




What if we look just at absolute magnitude of these brains?

This refers to the total size of a brain of a certain species, with no reference to body size or neuronal activity. If the organization of the brain as a whole is irrelevant, then total brain size seems an obvious candidate for use as an estimate of total information-processing capacity. If we used this as a comparison method, we would find that the largest brain sizes and highest brain weights are found in porpoises, elephants, and whales, followed by man (Figure 396- Kuhlenbeck). Whale brains weigh generally between 4000-7000 g, elephant brains around 4000-5000 g, dolphin brains around 1700 g, and human brains weigh between 1300-1700 g. Of course, remember that variations in brain weight within a species are quite considerable.

From this information, can we speculate that whales, with the largest total brain size, are therefore the most intelligent species? Let us look at a study reported by Kuhlenbeck (1973) with regards to intelligence and brain size. Studies of brains of "outstanding" or "genius" (link- what is genius? What is outstanding?) human individuals have been interpreted to show some statistical correlation between high brain weight and intellectual capacity. However, in individual cases, a person with a low brain weight around 1017g was highly gifted while another with a brain of 1800g was extremely mentally handicapped. In addition, one of the highest recorded human brain weights, mentions Kuhlenbeck, is said to have reached 2850g and this person was reported to be "an epileptic affected with idiocy" (Kuhlenbeck, 1973, 732). How does this affect our use of absolute magnitude of brain size to correlate with intelligence?

For another example, the average weight of a "typical" (link-what is typical?) adult male is +- 1400 while an adult female brain weight averages at +- 1300. Does this mean that males are more intelligent, more advanced than female humans? If we correlated large brain size with increased intelligence, then we would have to assume this comparison, yet on a whole it has not been documented that males are any more intelligent than females.

Thus, it seems that statistical correlation of brain weight and "superior intellectual ability" remains rather inconclusive. Therefore, perhaps we should find another method for comparing brain sizes and structures of various species.

Well, what about brain size versus body size?

Huh? Can we start over?