The Geological Congress in Russia
The Geological Congress in Russia. 951 tion " leaves a very large field of determinate evolution entirely uncovered and unexplained, and there remains a tertivm quid which requires further investigation. Determinate evolution in these non-plastic structures at present strikes me as part of the mechanical necessities of development, if I may so express it. That is, given a certain primitive form, there is only one route along which it can attain a certain end, provided the intervening stages are
... ervening stages are mechanically effective. It is some such law of mechanical necessity as this which out of the conical type of reptilian teeth has evolved first the triconodont type, the tritubercular, and finally the multitubercular, and from these main stages have arisen sub-stages which are repeated and independently acquired over and over again in different branches of the mammalian class. This is not an explanation, or a theory, it is a fact yet to be understood. Organic Selection constitutes a distinct advance, and is, at least, a very useful working hypothesis, but it is by no means the conclusion of the whole matter, as Alfred Wallace maintains. We must persevere in our analysis of life processes as revealed in living organisms and in fossils with a perfectly open mind, perhaps for many decades, perhaps for another century, before we reach final conclusions in regard to the complex processes of evolution. Columbia University.