Kaspar Friedrich Wolff

1733-1794

German Physiologist and Embryologist

Kaspar Friedrich Wolff, the author of Theory of Generation (1759), revived the theory of epigenesis during a period in which many of the most respected naturalists were advocates of preformationist theory. According to the theory of epigenesis, an embryo is gradually produced from an undifferentiated mass by means of a series of steps and stages during which new parts are added. Preformationist theories asserted that an embryo or miniature individual preexisted in either the egg or the sperm and began to grow when properly stimulated. Wolff, who was very much influenced by the mode of thought known as nature philosophy, engaged in a debate about epigenesis and preformationism with the great physiologist Albrecht von Haller (1708-1777).

Kaspar Friedrich Wolff was born in Berlin, where he studied at the collegium medicochirurgicum. He continued his studies at the University of Halle where he became fascinated by the ideas of Christian, freiherr von Wolff (1679-1754), professor of mathematics and philosophy. Wolff, who was known as the German spokesman of the Enlightenment, wrote numerous works in philosophy, theology, psychology, botany, and physics and a series of essays that all began with the title "Rational Ideas." Kaspar Wolff was impressed with his mentor's botanical work and his philosophical principle that everything that happens must have an adequate reason for doing so. According to the Wolffian system of philosophy, it was impossible for rational beings to believe that something might come out of nothing.

In 1759 Kaspar Wolff completed a dissertation entitled Theory of Generation, which became a landmark in the history of embryology. His work, however, brought him little recognition during his lifetime. After serving as an army surgeon, he gave private lectures on pathology and medicine in Berlin. Unable to obtain a professorial position at the Medical College of Berlin, in 1767 he accepted an invitation to go to St. Petersburg, Russia. He was appointed academician for anatomy and physiology and continued to conduct research for the remainder of his life.

Charles Bonnet (1720-1793), Lazzaro Spallanzani (1729-1799), and René Antoine Ferchault de Réaumur (1683-1757), as well as von Haller, were proponents of ovist preformationism. The debate between von Haller and Kaspar Wolff concerning the nature of embryological development provides important insights into the role of observation and metaphysical assumptions in scientific controversies. Von Haller's studies of the developing chick egg convinced him that the embryo could be found in the egg before the chicken laid the egg. He also accepted Bonnet's studies of parthenogenesis in aphids as compelling evidence for ovist preformationism.

Kaspar Wolff's theory of generation, in contrast, was founded on the philosophical assumption that development must occur by epigenesis. Unlike preformationists, Wolff believed that studies of generation could only be purely descriptive because it was impossible to determine the actual mechanism of development. When von Haller rejected Wolff's theory of generation on largely religious grounds, Wolff insisted that a scientist should only consider scientific evidence when investigating biological questions. Wolff, however, was also influenced by preconceptions that led him to seek out observations that supported epigenesis. Wolff and other advocates of nature philosophy believed that descriptive knowledge of the gradual development of different life forms was the basis for understanding vital (living) phenomena.

Wolff's essay on generation began with a series of definitions. Generation was defined as the formation of a body by the creation of its parts. The organs of the body did not exist at the beginning of gestation but were formed successively; each step led to the next step. Beginning with the assumption that the original undifferentiated materials were essentially the same in plants and animals, Wolff studied plant metamorphosis as well as the development of the chick egg.

Studies of the development of plants helped Wolff overcome the technological limitations of eighteenth-century microscopy since more details could be seen in plant materials than in unstained animal tissues. Wolff thought that liquid was drawn up to the growing parts of the plant where it became a kind of thin jelly. As liquid evaporated, small sacs, or vesicles, formed. Eventually, the ducts of the plant vascular system developed in the masses of vesicles. Wolff thought that similar processes occurred in the development of the chick embryo. It is not clear, though, whether the vesicles that Wolff reported seeing were actually cells. Wolff argued that development involved change as well as growth, but preformationism actually implied that development did not occur.

The growing influence of nature philosophy in the late eighteenth century made Wolff's philosophy more acceptable to naturalists than the mechanistic philosophy. The conflict between preformationism and epigenesis, however, was not resolved until the nineteenth century, when cell theory provided a new way to think about eggs, sperm, embryos, and organisms.

LOIS N. MAGNER