Page:Popular Science Monthly Volume 26.djvu/26

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16
THE POPULAR SCIENCE MONTHLY.

the class of mammals, exclusive of man, was as 1 to 186. My own observations accord very closely with those of Leuret. I found that in the prairie-wolf the proportion between the brain and the body was as 1 to 220; in the wild cat, as 1 to 158; and in the rat, as 1 to 132.

If these figures teach anything at all, it is that there is no definite relation existing between the intelligence of animals and the absolute or relative size of the brain. It is true that, taking the data collected by Leuret as the basis, there is a well-defined relation between the mental development and the brain, as regards the several classes of vertebrate animals; for in fishes, the lowest, the brain is but one 5,668th part of the body; in reptiles, the next highest, it is one 1,321st part; in birds, next in the ascending scale, it is one 212th part; and in mammals, the highest of all, one 186th part. There is, therefore, beginning with the lowest class, a regular ascent in the volume of the brain till it reaches the maximum in mammals.

But, when we look at the relation as it exists between the different orders and genera of any one class, we can not say that there is any such variation in the degree of mental development as we should expect to find if the brain were the only source of the intelligence, and some members of the very lowest class have relatively larger brains than certain animals of the very highest. Thus, the brain of the bass is to the body as 1 to 523, while in the horse it is but as 1 to 700, and in the ox as 1 to 750. If the relative size of the brain is to be taken as an indication of the degree of intelligence, we must regard the bass as a more intellectual animal than either the horse or the ox. The lizard has a brain which bears the high proportion to the body of 1 to 180. This is greater than that existing in the fox, the dog, the sheep, and several other mammals. The canary-bird and the Arctic sparrow have brains proportionately larger than those of any other known animals, including man, and yet no one will contend that these animals stand at the top of the scale of mental development. Man, who certainly stands at the head of the class of mammals, and of all other animals, so far as mind is concerned, rarely has a brain more than one fiftieth the weight of the body, a proportion which is much greater in several other mammals, and is, as we have seen, exceeded by many of the smaller birds.

Even in absolute weight, independent of any relation to the rest of the body, the brain of man is not the largest, being exceeded by that of the elephant and the whale. But, when we inquire into the matter of the absolute and relative quantity of gray nerve-tissue, we find that in this respect man stands preeminent; and it is to this fact that he owes the great mental development which places him so far above all other living beings, for it is the gray tissue which originates mind—the white, as is well known, serving only for the transmission of impressions and impulses. Unless regard is paid to this point, we should certainly fall into serious error in determining the relation