August Freidrich Leopold Weismann

views updated

August Freidrich Leopold Weismann

The German biologist August Freidrich Leopold Weismann (1834-1914) was one of the founders of the science of genetics.

August Weismann was born on Jan. 17, 1834, at Frankfurt am Main. He early showed intense interest in natural history, and while still a schoolboy he made extensive collections of butterflies, moths, beetles, and plants from the country around Frankfurt. He entered the University at Göttingen in 1852 and took a four-year course in medicine.

Weismann became an assistant in a hospital at Rostock (1856-1857) and then an unpaid assistant to a chemist in Rostock Chemical Institute. He soon decided he was not suited to chemistry and in 1858 went to Baden and to Italy as an army doctor. In 1861 he worked in Giessen for 2 months under Rudolf Leuckart, whom Weismann much admired and to whom he dedicated The Germ Plasm (1892). Weismann then obtained an appointment as private physician to the Archduke Stephen of Austria.

In 1863 Weismann joined the University of Freiburg im Breisgau as a privatdozent in the medical faculty, teaching zoology and comparative anatomy. In 1865 he was appointed professor extraordinarius, and thanks to his enthusiasm, a zoological institute and museum, of which he was appointed head, was built. About 1874 he was appointed professor ordinarius at Freiburg, being the first occupant of the chair in zoology in the university, where he remained until his retirement in 1912. He died in Freiburg on Nov. 5, 1914.

Early Embryological Work

Weismann's early research was mainly in the field of embryology. He published six classical studies on the embryonic and postembryonic development and metamorphosis of insects between 1862 and 1866. In a monograph on the postembryonic development of the Muscidae (1864), he described in detail the building up of the perfect form of the pupa, and he showed that in insects with a complete metamorphosis the tissues break down into an apparently simple, primitive mass, from which the imago is built up afresh by a kind of second embryonic development.

This work on insect development was followed by a series of memoirs on minute Crustacea and by a very thorough study of the sex cells of the Hydrozoa, which was published in four papers between 1880 and 1882. His eyesight became too weak for him to continue microscope work, and he turned to more general theoretical problems, such as heredity and reproduction.

Evolution Studies

From the first Weismann was a strong supporter of the theory of evolution by natural selection, as put forward by Charles Darwin and Alfred Wallace. In his book The Evolution Theory (2 vols., 1904) Weismann stated that Darwin's Origin of Species, when it was published in German in 1859, fell "like a bolt from the blue."

In spite of his enthusiastic support of Darwin, Weismann felt it necessary to disagree with that part of the theory in which Darwin had accepted the Lamarckian view of the inheritance of acquired characters. Weismann disagreed strongly with this concept, both on technical grounds and from experimental evidence (or the lack of it). He first publicly expressed his views on the matter in 1883 in the essay "Heredity, " presented as his inaugural address as prorector of the University of Freiburg. He pointed out the impossibility of proposing a mechanism whereby changes in the external organs and tissues of an animal, induced by environmental stimuli, would be conveyed to the reproductive organs and the germ cells within them and thence to ensuing generations.

Weismann realized it was necessary to suggest some other mechanism for producing the variations necessary for evolution. In this he was not very successful. He spoke as though natural selection could itself act in this way, but he was vague about the details. In The Germ Plasm he mentioned "chance nutritive fluctuations" in the germ plasm as giving rise to variations.

Germ Plasm Theory

The idea for The Germ Plasm appears to have stemmed from Weismann's early embryological studies, especially with Hydra, where he observed that only certain predetermined cells were capable of giving rise to the germ line and to daughter individuals. He extended the idea to the contents of these cells and proposed that there was a certain substance, or "germ plasm, " which could never be formed anew but only from preexisting germ plasm. It was transmitted unchanged from generation to generation and controlled all the characters of the individual animals. The idea of the germ plasm seemed (and seems) to some people to be somewhat mystical, as it postulates a completely self-determining substance, which apparently does not obey the laws of the physical world, since it proceeds along a path determined only by itself, unaffected by the surrounding environment.

Weismann made his germ plasm theory all-embracing, in that he attempted to explain not only heredity but also development. In fact, at times he seems to place greater significance on the latter aspect than on the former and allows his imagination to get rather out of hand. He proposed that the total hereditary substance of a cell should be called idioplasm. Every cell contained idioplasm, while the idioplasm of the germ cells was the germ plasm. The idioplasm was composed of smaller entities called ids. Each id in its turn consisted of determinants, each controlling the development of a particular part of the organism. The determinants contained certain groups of biophors, the simplest living units, which were thought to consist of "albumen molecules, water and salts."

Surprisingly, Weismann did not appear to appreciate the full significance of Gregor Mendel's work even after 1900. In The Evolution Theory, apropos Mendel's work, Weismann states, "We must postpone the working of this new material into our theory until a very much wider basis of facts has been supplied." (To most of us today, Mendel's experiments seem completely convincing.)

Yet in some respects Weismann was remarkably farseeing. In his discussion on the "inheritance" of musical ability and other cultural activities, he clearly sets out the distinction between biological heredity, based on a transmission of material through the germ cells, and cultural inheritance, resulting from a process of learning of skills and traditions by individuals of each generation from their parents and other individuals in the surrounding society. Again, in regard to the origin of life on earth, which Weismann discusses in the last chapter of The Evolution Theory, he dismisses the possibility that life was brought to the earth in a meteorite and comes out firmly in favor of spontaneous generation—not however of any form of life like that now familiar to us, but of some extremely primitive bodies (biophors). These "albuminoid substances, " he assumed, could have arisen spontaneously through purely chemicophysical causes, from inorganic materials, under conditions which may no longer exist on the earth. Such views are not far removed from the speculations on the origin of life currently in vogue.