Fig. 114.—August Weismann, Born 1834.
Permission of Charles Scribner's Sons.
Weismann, the Man.—The man who for more than forty years has been elaborating this theory (Fig. 114) is still living and actively at work in the University of Freiburg. August Weismann was born at Frankfort-on-the-Main in 1834. He was graduated at Göttingen in 1856, and for a short time thereafter engaged in the practice of medicine. This line of activity did not, however, satisfy his nature, and he turned to the pursuit of microscopic investigations in embryology and morphology, being encouraged in this work by Leuckart, whose name we have already met in this history. In 1863 he settled in Freiburg as privat-docent, and has remained connected with the university ever since. From 1867 onward he has occupied the chair of zoölogy in that institution. He has made his department famous, especially by his lectures on the theory of descent.
He is a forceful and interesting lecturer. One of his hearers in 1896 wrote: "His lecture-room is always full, and his popularity among his students fully equals his fame among scientists."
It is quite generally known that Weismann since he reached the age of thirty has been afflicted with an eye-trouble, but the inference sometimes made by those unacquainted with his work as an investigator, that he has been obliged to forego practical work in the field in which he has speculated, is wrong. At intervals his eyes have strengthened so that he has been able to apply himself to microscopic observations, and he has a distinguished record as an observer. In embryology his studies on the development of the diptera, and of the eggs of daphnid crustacea, are well known, as are also his observations on variations in butterflies and other arthropods.
He is an accomplished musician, and during the period of his enforced inactivity in scientific work he found much solace in playing "a good deal of music." "His continuous eye trouble must have been a terrible obstacle, but may have been the prime cause of turning him to the theories with which his name is connected."
In a short autobiography published in The Lamp in 1903, although written several years earlier, he gives a glimpse of his family life. "During the ten years (1864-1874) of my enforced inactivity and rest occurred my marriage with Fräulein Marie Gruber, who became the mother of my children and was my true companion for twenty years, until her death. Of her now I think only with love and gratitude. She was the one who, more than any one else, helped me through the gloom of this period. She read much to me at this time, for she read aloud excellently, and she not only took an interest in my theoretical and experimental work, but she also gave practical assistance in it."
In 1893 he published The Germ-Plasm, A Theory of Heredity, a treatise which elicited much discussion. From that time on he has been actively engaged in replying to his critics and in perfecting his system of thought.
The Mutation-Theory of De Vries.—Hugo de Vries (Fig. 115), director of the Botanical Garden in Amsterdam, has experimented widely with the growth of plants, especially the evening primrose, and has shown that different species appear to rise suddenly. The sudden variations that breed true, and thus give rise to new forms, he calls mutations, and this indicates the source of the name applied to his theory.
In his Die Mutationstheorie, published in 1901, he argues for the recognition of mutations as the universal source of the origin of species. Although he evokes natural selection for the perpetuation and improvement of variations, and points out that his theory is not antagonistic to that of natural selection, it is nevertheless directly at variance with Darwin's fundamental conception—that slight individual variations "are probably the sole differences which are effective in the production of new species" and that "as natural selection acts solely by accumulating slight, successive, favorable variations, it can produce no great or sudden modifications." The foundation of De Vries's theory is that "species have not arisen through gradual selection, continued for hundreds or thousands of years, but by jumps through sudden, through small transformations." (Whitman's translation.)
The work of De Vries is a most important contribution to the study of the origin of species, and is indicative of the fact that many factors must be taken into consideration when one attempts to analyze the process of organic evolution. One great value of his work is that it is based on experiments, and that it has given a great stimulus to experimental studies. Experiment was likewise a dominant feature in Darwin's work, but that seems to have been almost overlooked in the discussions aroused by his conclusions; De Vries, by building upon experimental evidence, has led naturalists to realize that the method of evolution is not a subject for argumentative discussion, but for experimental investigation. This is most commendable.