418 THE STRUCTURE OF EVOLUTIONARY THEORY
The (not so contradictory) sources of the mutation theory
Hugo de Vries became the world's most celebrated evolutionist during the early
20th century. His Mutationstheorie received wide approbation as the most
important proposal about evolutionary mechanisms since the Origin of Species and
the theory of natural selection. He made three triumphant visits to the United States
(in 1904, 1906, and 1912) and published two books in English (de Vries,
1905,1907a) based on summer lectures at the University of California, Berkeley.
His views therefore became especially well known to American and other English-
speaking audiences. All professionals continue to recognize his name today, but his
ideas have suffered a nearly total eclipse for two major reasons, one legitimate and
one unfair.
For the legitimate source, de Vries chose an unfortunate research strategy— a
botanical equivalent of putting all his eggs in one basket. His theory—based
largely on results from a single species, the evening primrose Oenothera
Lamarckiana—requires that his chosen exemplar represent a biological norm in
order to grant the required generality to his proposed mechanism. But the "species
forming" saltations of Oenothera were soon revealed as oddities of an unusual
chromosomal system, for Oenothera Lamarckiana is a permanent heterozygote, a
hybrid with chromosomes of each component linked in rings, and thus segregating
together in meiosis. (Only half the seeds are viable, because both homozygotes are
lethal.)
For the unfair reason, de Vries has been so identified with an almost
accidental moment of enduring fame that we have lost the main thrust and rationale
of his life's work. Such moments often inspire catechistic one-liners that persist as
the instant legacy of great thinkers. De Vries has suffered even more than most
scholars caught in such a predicament, for he became the subject of two knee-jerk
catechisms:
- Mendel's forgotten work of 1865 was independently rediscovered in 1900
by Hugo de Vries, Carl Correns, and Erich Tschermak-Seysenegg. - Ironically, the first application of Mendelism to evolutionary theory did
not help to affirm Darwinism, but to assert yet another alternative mechanism of
change—the saltatory origin of new species by macromutation. The Modern
Synthesis, the true fusion of Darwin and Mendel, began two decades later when
scientists finally realized that small-scale (Darwinian) variation could also claim a
particulate basis, and that macromutations played no important role in evolution.
We may praise de Vries as a rediscoverer of Mendel, but his own interpretation of
particulate inheritance delayed a proper resolution.
Neither of these conventional accounts can be dismissed as false, but neither
properly expresses the reasons for de Vries' interests and discoveries. His link with
Mendel represents a relatively minor encounter en passant in a career dedicated to
other concerns. De Vries did discover the Mendelian segregation laws during the
1890's, and he did demonstrate their occurrence in some 20 species. As he
prepared to publish this work in early 1900, his colleague, Professor Beyerinck at
Delft, sent him an old paper with the following