Principles of western civilisation

I PROJECTED EFFICIENCY 45

was a remarkable essay * read before the association of German naturalists held at Salzberg in 1881, seven months after Darwin's death. The writer was Professor August Weismann, of the University of Freiburg in Breisgau. In this paper the causes which determine the duration of individual existence in various forms of life were discussed from a point of view which at once attracted notice. Hitherto the prevailing opinions as to the causes which determine the average length of individual life may be said to have run along two main lines, with which readers of Mr. Herbert Spencer’s Bzology will be familiar. According to one theory, to which Leuckart and other writers had given support, and which may be called. the theory of external control, the duration of life was to be taken as determined by the size of the individual and the complexity of its structure. Or briefly, to put it in terms used by Mr. Spencer, greater length and degree of life were to be regarded as a necessary accompaniment of greater integration.” According to the other view, which may be described as the theory of internal control, length of life was to be taken as related to the structure, and inherent chemical constitution, of the cells of which the body was composed. It was believed to be largely influenced by the rate at which the vital processes take place, inertness of habit contributing to relatively great length of life, and vzce versa. Down to the time at which Professor Weismann’s paper was published, it was admitted that there were great and unexplained difficulties in the way of both views, a large class of facts being quite

1 The Duration of Life.

2 Principles of Psychology, $172. See also Principles of Biology, §§ 31-71. cp ycholog ip 1) 3