If the change in the conditions of vegetation were the only cause for variability, one would expect that those cultivated plants which have been grown for centuries under almost constant conditions would revert again to stability. As is well known this is not the case, for it is precisely among such plants that not only the most varied, but also the most variable forms are found.

We can compare this language to that used in one of Darwin’s paragraphs in The Origin: “No case is on record of a variable organism ceasing to vary under cultivation. Our oldest cultivated plants, such as wheat, still yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification.” Most importantly, however, it seems that Mendel may have realized that his theory of heredity could solve Darwin’s main problem: an adequate supply of heritable variations for evolution to influence. This was precisely where blending inheritance was failing, as pointed out by Jenkin. Mendel wrote:

If it be accepted that the development of hybrids takes place in accordance with the Law established for Pisum [peas], each experiment must be undertaken with a great many individuals . . . In Pisum it has been proved by experiment that hybrids produce ovules and pollen-grains of differing constitutions, and that this is the reason for the variability of their offspring.

In other words, inherited variation, and no blending at all. Moreover, Mendel tried several times to create variations in plants by removing them from their natural habitat to his garden at the monastery. When this failed to produce any change, Mendel told his friend Gustav von Niessl, “This much already seems clear to me, that nature does not modify species in any such way, so some other force must be at work.” Mendel therefore accepted at least some parts of the theory of evolution. This, however, raises another intriguing question: If Mendel agreed with Darwin’s concepts, and maybe even recognized the importance of his own results for evolution, why didn’t he mention Darwin by name in his writings? To answer this question we have to understand Mendel’s special historical circumstances. On September 14, 1852, the Austrian Emperor Francis Joseph I empowered Prince-Bishop Rauscher to act as his representative in drawing up a concordat with the Vatican. This concordat was signed in 1855, and in reaction to the winds of change in Europe in 1848, it contained strict regulations such as: “All school instruction of Catholic children must be in accordance with the teachings of the Catholic Church . . . The bishops have the right to condemn books injurious to religion and morals, and to forbid Catholics reading them.”

As a result of these restrictions, for instance, the paleontologist Antonén Fri was not even allowed to lecture in Prague, Czechoslovakia, on his impressions from a scientific meeting in Oxford in 1860 in which Huxley presented Darwin’s theory. Although the Vatican itself delayed official pronouncements on Darwin’s theory for many decades, a council of German Catholic bishops did state in 1860: “Our first parents were formed immediately by God, therefore we declare that the opinion of those who do not fear to assert that this human being . . . emerged finally from the spontaneous continuous change of imperfect nature to the more perfect, is clearly opposed to Sacred Scripture and to the Faith.” In this rather oppressive atmosphere, Mendel, who was ordained a priest in 1847 and elected abbot of the monastery in 1868, probably did not think it prudent to express any explicit support for Darwin’s ideas.