Gregor Mendel and the theory of species multiplication.

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According to the revisionist interpretation of Mendel’s pea crosses, his primary aim was not to study the inheritance of traits. Instead, he was interested in the question raised by Linnaeus as to whether new species could arise from the hybridization of existing species. The genetic interpretation is therefore seen as ahistorical by the revisionists. This view goes back to the 1979 article “Mendel no Mendelian?” by the historian of science R.C. Olby. A closer analysis shows that Olby implicitly assumed Mendel adhered to the unusual strictest species definition for Pisum. However, we argue that Mendel only mentions the hypothetical application of this strict definition in his 1866 paper. Like most of his contemporaries, Mendel accepted variation within species where the differences between varieties and species were a matter of degree. After researching variable hybrids in peas (Pisum; 1854-1863), Mendel also studied constant hybrids in hawkweeds (Hieracium; 1866-1873), which he considered to be new species. There is no debate about the latter, but the matter becomes muddled because Olby lumps Pisum and Hieracium together, despite their having completely different reproduction systems. Based on newly discovered historical sources, we also dispute several other assumptions made by Olby. We do not consider Olby’s claim that Mendel conducted the Pisum experiments to investigate species multiplication to be tenable.