456 The American Naturalist. [June, 



nection between the intricate metamorphoses in these cells and 

 the external phenomena of heredity, and more than this, to 

 realize that the heredity theory of the future must rest upon a 

 far more exact knowledge than we enjoy at present of the his- 

 tory of the reproductive cell both in itself and in the influ- 

 ence which the surrounding body cells have upon it. 



These advances affect the problem of life and protoplasm, 

 whether studied by the physician, the anthropologist or the 

 zoologist, thus concentrating into one focus opinions which 

 have been formed by the observation of widely different classes 

 of facts. As each class of facts bears to the observer a differ- 

 ent aspect and gives him a personal bias, the discussion is by 

 no means ironical, and it is our privilege to live through one 

 of those heated periods which mark the course of every revo- 

 lution in the world of ideas. Such a crisis was brought about 

 by the publication of the theory of Darwin, in 1858, and after 

 subsiding has again been roused by Weismann's theory of 

 heredity, published in 1883. 



This is the situation I have ventured to present to you as 

 Cartwright lecturer, not, of course, without introducing some 

 conclusions of my own, which have been derived from verte- 

 brate palaeontology, but which I shall direct mainly upon 

 human evolution. 



So far as theories need come before us now, remember that 

 Lamarck (1792) attributed evolution to the hereditary trans- 

 mission to offspring of changes (acquired variations) caused 

 by environment and habit in the parent. Darwin's latest 

 view was that evolution is due to the Natural Selection of such 

 congenital variations as favored survival, supplemented bythe 

 t ransmi8sion of acquired variations. Weismann entirely denies 

 the transmission of acquired variations or characters, and 

 attributes evolution solely to the natural selection of the indi- 

 viduals which bear the most favorable variations of the germ 

 or reproductive cells. We must, therefore, clearly distinguish 

 between " congenital variations " which are part of our inherit- 

 ance and " acquired - variations " which are due to our life- 

 habits ; the question is, Are the latter transmitted ? 



