Biology - Winter 1999

Why does progress in science sometimes take so long? What are the impediments to scientific discovery and the acceptance of new scientific ideas? To what extent is scientific progress limited by technology versus cultural and religious factors? These are the basic questions we will address in this course using, as a case history, the discovery of sexuality in plants.

Whereas it is likely that sexuality in animals was recognized at least 12,000 years ago, and probably a good deal earlier, sexuality in plants was not discovered until 1682, with the publication of Nehemiah Grew's Anatomy of Plants, and was not universally accepted until Darwin's day, nearly 200 years later. Considering how central plants are to civilization (plants were domesticated prior to the domestication of animals) it is remarkable that it took so long for people to understand the true sexual nature of flowers and the role of pollen in fertilization. In fact, if one reads the botanical writings of Aristotle and Theophrastus it is clear that the idea of sexuality in plants had been considered and rejected by the Greeks. This inability to accept the idea of sexuality in plants, especially the hermaphroditic nature of the flower, due to certain preconceptions and prejudices regarding the pristine and essentially female (and parthenogenic) nature of plants, was played out repeatedly over the centuries. Even after the idea was put forward by Grew and promulgated by Linnaeus, the issue was hotly debated and, in some quarters, fiercely resisted.

I. Prehistory- the archaeological evidence for the early discovery of sexuality in animals; the uses of plants in agriculture.

II. The Greeks: the botanical writings of Arisototle and Theophrastus: Greek notions about plant reproduction.

III. Middle Ages to Renaissance: Avicenna's refinement of Greek ideas; the European Herbals.

IV. Nathaniel Grew and Early Microscopists: direct observations of flowers.

V. Early hybridizers: Crossing experiments suggest sexual reproduction.

VI. Camerarius: The first careful experiments demonstrating the role of pollen in fertilization.

VII. Koelreuter: The first definitive demonstration of the role of pollen in hybridization.

VIII. Linnaeus/E. Darwin- Adopted the sexual system as a means of plant classification and popularized the idea. By attributing the human emotions of lust and passion to plants, they caused a reaction against the idea of plant sexuality.

IX. Nature Philosophers, including Goethe: Resisted the notion of plant sexuality as too vulgar and crude.

X. Sprengel, C. Darwin, Mendel. Sprengel discovered the role of insects in pollination. Darwin was strongly influenced by Sprengel. Mendel discovered the laws of inheritance using plants.

XI. Hofmeister and Alternation of Generations: The last bastion of opposition to plant sexuality falls. Sexuality discovered and elucidated in gymnosperms and lower plants ("cryptogams": algae, bryophytes, and ferns). Discovery of the unifying principle of "alternation of generations".

XII. The modern view of plant flowers: an overview of modern research on plant reproduction.

Revised 7/23/04.