AMERICAN NATURALIST A BI-MONTHLY JOURNAL DEVOTED TO THE ADVANCEMENT OF THE BIOLOGICAL SCIENCES VOLUME LVI NEW YORK THE SCIENCE PRESS AMERICAN NATURALIST VOL. LVI. January February No. 642 THE ORIGIN OF VARIATIONS SYMPOSIUM AT THE THIRTY-NINTH ANNUAL MEETING OF THE AMERICAN SOCIETY OF NATURALISTS, TORONTO, DECEMBER 29, 1921 VARIATION IN UNIPARENTAL REPRODUCTION PROFESSOR H. S. JENNINGS THE JOHNS HOPKIN'S UNIVERSITY DARWINISM left the origin of variations the unsolved problem. Give us inherited variations, it said, and we can explain adaptation, by natural selection. But this was the omission of 99 per cent., if not 100 per cent., of the problem of evolution. Are we in better case to-day? Has the experimental study of genetics given us some solid knowledge of the origin, the causes, of variation? Have we learned that the obvious differences observable everywhere among individuals are the foundations of evolution? Or that they are not? Are slight quantitative fluctuations the material out of which evolution is made? Have we discovered that extensive saltations are the steps in evolution? Or that less extensive mutations, qualitative or chemical changes, that may be minute or large, are that by which evolution is constituted? Do we know the origin of such saltations, mutations? Have we found that the present constitution of the organism predetermines in some way the course of further change; or that an élan vital is driving the organism to unfold in a definite way, like a flower; that evolution is orthogenesis? Do we comprehend the nature and causes of such a push to unfold, and of the direction in which it tends? Have we found perhaps, as at least one investigator maintains, 5 |