Mendel Gregor (1822–84), Austrian botanist and discoverer of what are now considered the basic principles of heredity. An Augustinian monk who conducted plant-breeding experiments in a monastery garden in Brünn (now Brno, Czech Republic), Mendel discovered that certain characters of a common variety of garden pea are transmitted in a strikingly regular way. The characters with which he dealt occur in two distinct states, e.g., pods that are smooth or ridged. In characters such as these, one state is dominant to its recessive partner, i.e., when varieties of each sort are crossed, all the offspring exhibit the dominant character. However, when the offspring of these crosses are themselves crossed, the result is a ratio of three dominants to one recessive. In modern terms, pairs of genes (alleles) separate at reproduction (segregation) and each offspring receives only one member of each pair. Of equal importance, the recessive character reappears unaffected by its temporary suppression. Alleles remain pure. Mendel also noted that the pairs of characters that he studied assort independently of each other, i.e., if two pairs of characters are followed through successive crosses, no statistical correlations in their transmission can be found. As genetics developed after the turn of the century, the simple ‘laws’ that Mendel had set out were expanded and altered. Only a relatively few characters exhibit two distinct states, one dominant to the other. In many, the heterozygote exhibits an intermediate state. In addition, genes do not exist in isolation from each other but together on chromosomes. Only those genes that reside on different pairs of chromosomes assort in total independence of each other.
During his research, Mendel corresponded with Karl von Nägeli (1817–91), a major authority in plant hybridization. Von Nägeli urged Mendel to cross varieties of the common hawkweed. When Mendel took his advice, he failed to discover the hereditary patterns that he had found in garden peas. In 1871 Mendel ceased his research to take charge of his monastery. In 1900 Hugo de Vries (1848–1935) stumbled upon several instances of three-to-one ratios while developing his own theory of the origin of species. No sooner did he publish his results than two young biologists announced independent discovery of what came to be known as Mendel’s laws. The founders of modern genetics abandoned attempts to work out the complexities of embryological development and concentrated just on transmission. As a result of several unfortunate misunderstandings, early Mendelian geneticists thought that their theory of genetics was incompatible with Darwin’s theory of evolution. Eventually, however, the two theories were merged to form the synthetic theory of evolution. In the process, R. A. Fisher (1890–1962) questioned the veracity of Mendel’s research, arguing that the only way that Mendel could have gotten data as good as he did was by sanitizing it. Present-day historians view all of the preceding events in a very different light. The science of heredity that developed at the turn of the century was so different from anything that Mendel had in mind that Mendel hardly warrants being considered its father. The neglect of Mendel’s work is made to seem so problematic only by reading later developments back into Mendel’s original paper. Like de Vries, Mendel was interested primarily in developing a theory of the origin of species. The results of Mendel’s research on the hawkweed brought into question the generalizability of the regularities that he had found in peas, but they supported his theory of species formation through hybridization. Similarly, the rediscovery of Mendel’s laws can be viewed as an instance of multiple, simultaneous discovery only by ignoring important differences in the views expressed by these authors. Finally, Mendel certainly did not mindlessly organize and report his data, but the methods that he used can be construed as questionable only in contrast to an overly empirical, inductive view of science. Perhaps Mendel was no Mendelian, but he was not a fraud either. See also DARWINISM. D.L.H.