204 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



its green carpet of "wise turf" which in some form clothes by far the 

 greater part of the land of the globe. 



The kind of developmental reaction of which this is but a single 

 example must clearly have had influence on bodily features other 

 than bones and horns, teeth and claws, speed and strength; and one 

 of the most striking has been on intellectual development and the 

 size and shape of brain. 



We do not, and perhaps can never, know the quality of the mate- 

 rial of which the brains of fossil creatures was made, for we have no 

 instrument to pierce the veil of time as the spectroscope has pene- 

 trated the abysm of space. But we are even now learning something 

 about their shapes and convolutions, and more about their mass in 

 its relation to the size of the bodies controlled; from the time of 

 the earliest Ordovician fishes, through the history of the amphibia, 

 reptiles, birds, and mammals, up to man himself. 



The brain of those gigantic if somewhat grotesque reptiles, the 

 dinosaurs, the tyrants of Mesozoic time, is relatively tiny. In Diplo- 

 docus, 80 feet in length and 20 tons in weight, the brain was about 

 the size of a large hen's egg. It is true that there was a big supple- 

 mentary sacral ganglion which may have taken chief charge of 

 locomotion and helped to secure coordination throughout the hinder 

 part of its huge length and bulk; but of true brain there was not 

 more than a quarter of an ounce to control each ton of body and 

 limb; and we begin to understand why they lost the lordship of 

 creation. 



The proportion of brain to body improved in those reptiles which 

 took to flying, possibly in relation to their acquisition of warm blood, 

 and in the birds evolved from reptiles; but it is only in mammals 

 that a marked advance is seen. Here the brain of IJintatherium, a 

 great rhinoceroslike animal of Eocene date, weighing 2 tons, was 

 about the size of that of a dog. This proportion of half a pound 

 of brain to each ton of body shows how far the mammals had gone, 

 and still had to go. 



A 12-stone man of the present day has about 3I/2 pounds of brain — 

 an amount not far short of half a hundredweight per ton. 



Even though we can know nothing of its material, this steadfast 

 growth in the guiding principle, through the millions of centuries 

 that have gone to its development, is surely one of the most remark- 

 able conclusions that we owe to geology. Of all the wonders of the 

 universe of which we have present knowledge, from the electron to 

 the atom, from the virus and bacillus to the oak and the elephant, 

 from the tiniest meteor to the most magnificent nebula, surely there 

 is nothing to surpass the brain of man. An instrument capable of 

 controlling every thought and action of the human body, the most 



