Linnaeus on evolution by hybridism

It is often stated in the literature that Linnaeus late in life turned to an evolutionary view based on hybridisation (e.g., Clausen, Keck and Hiesey 1939). I myself have repeated this, but as always it’s worth looking at the actual text. Unfortunately I have so little Latin that I can’t even use pig Latin, so it is great to find, yet again, that archive.org has it in an English edition published in 1783. I love archive.org. Deeply.

It’s in the context of what he bases his system on, the “fructification” of the plants; i.e., the reproductive organs:

26. The PRINCIPLE of Fructification, the Foundation of Botany, should be traced higher.

Problem: we may suppose God at the beginning to have preceded from simple to compound, from few to many! and therefore at the beginning of Vegetation to have created just so many different plants, as there are Natural Orders. That He then so intermixed the plants of these orders by their marriages with each other; that as many plants were produced as there are now distinct Genera. That Nature then intermixed these Generic plants, by reciprocal marriages, (which did not change the structure of the flower) and multiplied them into all possible existing Species; excluding however from the number of Species, the Mule-plants produced from these marriages, as being barren.

Each Genus therefore is natural, Nature assenting to it, if not making it.

The Character therefore never constitutes the genus, but is itself diligently to be constructed according to the Genus of Nature.

Kindred Plants of the same mother, are to be known in respect to the Genus by the flower, or displayed plant, when the reciprocal undulterated marriage leaves the Fructification entire; but in the species are to be diftinguished from their sister-companions, produced by a different father, according to the Herb.

Thus the Diagnosis of a plant consists in the affinity of the Genus, and in the difference of the Species.

The Name of a plant therefore, that it may refer to each diagnosis, is double:

   the Generic Family Name,

   And the Specific trivial Name,

under which latter are the vague Synonymies of authors.

The Botanist, in following the Classifications, is lead to the named Genus by the Characters of the displayed plant or flower; to the appellation of the Species by the Differences of the Larva or herb; and thence to its Synonymies; from these to Authors, and thence to every thing, which has come to us from our ancestors on the subject. Thus the plant itself tells its Name, and its History amid such a multitude of species, and of individuals; this is the great purpose of Botany, the invention of the present age, to the completion of which all true Botanists will contribute their labour.

In other words, Linnaeus makes the following claims:

1. All propensities were created once, as the “Natural Orders”, and recombination of these generates genera (which are in his eyes natural, unlike modern views of taxonomic ranks above the species level), and again into species.

2. To be an infertile species, a “mule”, is not to be a species at all. This means that for Linnaeus, a species is a reproductive group. I therefore must take back what I have elsewhere said about Staffan Müller-Wille’s (2007) claim that Linnaeus had a “biological” species concept; indeed he can be interpreted that way. Too late for the book, alas…

3. Diagnosis relies upon “affinity”, and not a single Character, at least in a natural system. I am coming to the conclusion that “affinity” is a kind of vaguely expressed notion of the sum of homologies between taxa, and it become extremely important in the later writings of taxonomists, especially in French and English taxonomy, as botanists attempted to create a “natural system” along the lines of Jussieu. That Linnaeus mentions it here is of great interest to me.

4. Note that Characters are not the essence of the Genus or Species, but “lead the botanist to the Genus”. They are diagnostic rather than constitutive. The famous botanist John Lindley also makes this distinction explicit in his Introduction to the Natural System in 1831, so the term’s life exceeds just the Linnaean scheme. I believe this was greatly influential on Darwin’s ideas, as Polly Winsor also does in general terms (2009), as I have discussed previously.

This is a later view of Linnaeus’, not his views that made his career. It became interesting after Darwin made transmutationism respectable, and people went looking for precursor views. He is not, however, in any real sense an evolutionist – the new species arise as the recombination of prior characters and mechanisms that already existed. There’s no novelty.

References

Clausen, Jens, David D. Keck, and William M. Hiesey. 1939. The concept of species based on experiment. American Journal of Botany 26 (2):103-106.

Linnaeus, Carl. 1783. A system of vegetables, according to their classes orders genera species with their characters and differences. 2 vols. Vol. 1. London: Botanical Society, at Lichfield. Printed by John Jackson, for Leigh and Sotheey. Original edition, Translated from the [1774] thirteenth edition (as published by Dr. Murray) of the Systema Vegetabilium of the late Professor Linneus; And from the Supplementum Plantarum of the present Professor Linneus.

Müller-Wille, Staffan, and Vitezslav Orel. 2007. From Linnaean Species to Mendelian Factors: Elements of Hybridism, 1751-1870. Annals of Science 64 (2):171-215.

Mary P. Winsor (2009). Taxonomy was the foundation of Darwin’s evolution. Taxon, 58 (1), 1-7