We have hesitated in choosing this title because it is identical with that of Bergson's masterly work. Bergson was perhaps the most eminent philosopher to build his philosophical views in part on the basis of biological evolutionism. The biological knowledge which was available in Bergson's time is however now out of date. Our present understanding of evolution is rather different from his. This is as it should be. Science is cumulative knowledge. A scientist works to make the knowledge whith which he started obsolete. In a very real sense he works to make his own work obsolete as well. In so far as a philosophy has science as one of its components, or supports, philosophy must be rethought, reconstructed, and reformulated from the vantage point of each generation. If all conclusions based on scientific knowledge of a half century ago were still valid, this could only mean that the study of the evolution of life is no longer profitable. Such however is not the case.