Looking at the Absolute Magnitude of the Brain

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 (go to brain/body size chart). Whale brains weigh generally between 4,000-7,000 g, elephant brains around 4,000-5,000 g, dolphin brains around 1,700 g, and human brains weigh between 1,300-1,700 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" 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 1,017 g was highly gifted while another with a brain of 1,800 g was extremely mentally handicapped. In addition, one of the highest recorded human brain weights is said to have reached 2,850 g 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 brain weight of a "typical" adult male is +- 1,400 g while an adult female brain weight averages at +- 1,300 g. Does this mean that males are more intelligent and 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.

Don't forget that there are multiple methods for studying the brain and its relationship to behavioral complexity. Let's take an indepth look at the other methods, which include:

• measuring brain size versus body size
• measuring cortical folding
• measuring neocortex
• measuring volume of gray matter versus volume of nerve cells
• looking at specific brain structures