Title page & Abstract

Introduction

Methods

Discussion
of Methods

Table

Results

Figure 3

Discussion

References

Although our thesis is a new one, concern with brain size is very ancient, From the time of Aristotle, who noted that "of all animals, man has the largest brain in proportion to his size," the relationship between brain weight and body weight has been calculated for various vertebrate species and related to the question of the comparative intelligence of these species. The early work of Perrault (1613-1688), Vicz-d'Azyr (1748-1794), and Cuvier (1769-1832) on this question has been reviewed by Cole (16) and Coleman (17). Considerable attention was devoted to it by Manouvrier and Dubois at the end of the 19th century, as summarized by Anthony (1). In recent years, the relationship of brain weight and body size and its significance for intelligence has been considered in detail by Jerison (44, 45).

The relationship of brain size to body weight across different vertebrates is not a simple function. It is an exponential function with an exponent close to 0.66 depending on the group of animals under consideration. Furthermore, it is necessary to construct at least two different equations, one for cold-blooded vertebrates and another for warm-blooded vertebrates, since values for the latter are somewhat more than 1 log decade greater than those of the former for animals of the same weight.

We noticed that the graphic representation of brain weight as a function of body weight was strikingly similar to the graphic representation of basal metabolism as a function of body weight. On logarithmic axes, cold-blooded and warm-blooded vertebrates lie along two separate lines with similar slopes (approx 0.66) and with y intercepts that differ by somewhat more than 1 decade, no matter whether the equations represent brain weight (45) or basal metabolism (36) as a function of body weight. The great similarity of the functions suggested that they might reflect a simple underlying relationship of size of the nervous system to basal metabolism.

The possibility of a relationship between brain size and body metabolism has been considered before. Benedict (8) briefly discussed the role of the brain in controlling metabolism and concluded that it cannot be demonstrated that brain size is the controlling factor in metabolism. Based on blood circulation and brain weights of "lower" animals, the German neurologist Kestner (48) concluded erroneously that about 40% of the oxygen consumption may be attributed to the brain. Finally, Crile (19), on the basis of detailed measurements of the organs of many vertebrates, came to a conclusion similar in some respects to the one considered here

We found a law, so fundamental that it embraces insects, fish, reptiles, birds, rodents, ungulates, and carnivores, but not higher apes and man. This law is expressed by the ratio between the weight of the brain of an animal and the number of calories produced by that animal in 24 hours. We found that 1 gram of brain is required to produce 12,115 small calories in 24 hours.