It has been a controversial question whether the natural selection principle has, to some extent, a necessary or a contingent, a causal or a random character. In this paper I advance an argument based on several prominent theoretician of evolution for the extrinsic random character of the processes of natural selection since they are permeated by external chance factors—climatic, atmospheric, geological, and even astronomical. At the same time, I consider that natural selection, as the principal mechanics of evolution, is a causal mechanics. The apparent tension that the former present can be dissolved if one agrees that in evolution the causal factors are probabilistic whereas the chance is objective. In order to reformulate the natural selection principle I will apply Suppes probabilistic theory of causality as the formal apparatus. By doing this I intend to provide some support to the thesis that principle of Darwin’s theory of evolution is a probabilistic principle