Reception

Contemporaries were only too happy to accept Koelreuter's conclusions. The rigor and complexity of his experiments were alien to

[55] Ibid., 189.

[56] "At no time," writes Ernst Mayr, "did he partition the phenotype into individual characters and trace the fate of a given character in different combinations through several generations." Ernst Mayr, The growth of biological thought. Diversity, evolution, and inheritance (Cambridge, Mass.: Belknap Press, 1982), 646.

the mentality of many naturalists of the late 18th century, but his results supported very powerfully the theory of limited variability then being elaborated. Nor was Koelreuter's work so obscure or inaccessible that no one read it. Christian Sprengel took up Koelreuter's work on pollination, arguing that floral structure was an adaptation to secure pollination and showing that cross-fertilization was the rule rather than the exception. C.F. von Gärtner, an erudite and industrious plant hybridizer reaffirmed Koelreuter's entire theory of generation. His evidence consisted of the results of nearly 10,000 separate crossing experiments among 700 species. As Koelreuter's Vorläufige Nachricht and the three Fortsetzungen were published, a reviewer in the Göttingsche Anzeigen astutely picked out the tendency of the argument. Not only had Koelreuter limited severely the possibility of novelty by means of species crosses; he had shown that change was a narrowly defined combinatory of already existing characters.^[57]

These summaries, and mémoires published by Koelreuter between 1770 and 1796 in the Commentarii and Acta of St. Petersburg, were read, assimilated, and commented upon by two of the most influential and widely read naturalists of the period, Johann Friedrich Blumenbach and Peter Simon Pallas. In his first important work on the theory of generation, Blumenbach presented Koelreuter's experiments as a refutation of preformation. The very possibility of specific bastards contradicted any conception of preformed germs, while Koelreuter's transformation of one species into another "must undeceive even the most partisan defender of the theory of evolution [i.e., preformationist] from his prejudice."^[58]

Peter Simon Pallas claimed that Koelreuter had instituted "experiments on plant crosses the results of which absolutely contradict the opinion of the Chevalier Linné." He continued:^[59]

The great difficulty we have in producing crosses, with all our human industry, between two different species, the impossibility, confirmed by fact, of perpetuating these as crosses or as distinct races, either because of their

[57] Göttingsche Anzeigen von gelehrten Sachen , St. 102 (1762), 889–91; St. 36 (24 Mar 1764), 281–4; St. 26 (28 Feb 1767), 207–8.

[58] Blumenbach, Uber den Bildungstrieb , 61.

[59] Pallas, "Memoire sur la variation des animaux," 74–5.

absolute or relative infertility, or because of the regressive degeneration to which their issue is subject, since these crosses require for fertilization the aid of one of their primitive branches, all this opposes facts to a simple probability and forces us to see that all those species that nature affects to render alike as primitive, projected in the first plan of creation, and destined to form that chain of beings that we admire without being able to account for it, any more than [we can account for] the choice, harmony, and combination of colors and ornaments that the same creative force has used to embellish its works.

The experiments Koelreuter undertook to discover the reproductive limits of plant species may seem commonplace. Older natural history had a modest experimental tradition and breeding experiments utilizing plants and animals were common after 1750. Koelreuter was unusual, however, in his diligence and energy: his experiments involved 138 species and over 500 hybridizations, and required him to examine pollen grains from more than 1,000 different species of plants.^[60] No other experimental sequence in natural history equals Koelreuter's in extent.

Koelreuter's use of counting and measurement in the analysis of his data was also unusual in 18th-century natural history. Although his contemporaries were masters of impersonal, objective, precise observation, naturalists throughout the 18th century ignored or resisted the use of mathematical methods and symbols in their studies of morphobiology. Natural history, as they understood it, was observational, qualitative, and finalist. The central conceptual tradition was Aristotelian, with its depreciation of mathematics as irreconciable with the study of final causes.^[61] Thus a resistance to measuring and counting came naturally to 18th-century natural history.

Not all naturalists were Aristotelians, however, and even the diehards of the Aristotelian tradition found it impossible to resist the forces toward greater precision that originated in more prestigious spheres of the scientific constellation. Anatomy contributed to the establishment of species characters the procedure of measuring size. Naturalists also counted seeds and pollen grains, observed numerical

[60] Olby, The origins of Mendelism , 21.

[61] As explained in Aristotle, Metaphysics , B 2 996a.

ratios, noted numbers of progeny, and proposed mathematical nomenclatures. These efforts toward quantification, however, remained sporadic and uncorrelated; and most naturalists considered the complexity of living forms beyond the power of mathematical analysis.

Koelreuter limited his concern to the boundaries imposed by nature upon crosses between two plant species—"the most confused knot in the entire doctrine of reproduction." He did not intend to untie the knot, but rather to identify its major features. Since only two plant species were involved in any one cross, Koelreuter conceived his problem as analogous to a combinatory. Because specific differentia were susceptible to measure and enumeration, combinations could thus be expressed as a simple sum or difference. Koelreuter applied the instruments of measurement and counting with unusual consistency. The design and scale of his experiments permitted him to determine different forms and sizes of hybrid offspring, arrange them by generation, and estimate their ratios. That his quantitative approach yielded important results was due in large measure to his stubborn concentration on carefully limited problems of plant morphology.