Charles Darwin and Gregor Mendel were contemporaries, but did they know of each other’s work? There is clear evidence that Mendel read “The Origin of Species,'' and mounting evidence that Darwin had heard of Mendel’s work.
The respective places of these two men in the scientific world at the time were worlds apart. Darwin’s theory took the scientific world by storm when his famous book was published in 1859—everyone was talking about it.
Mendel’s work, presented to the Brunn Society of Natural History in 1865, remained largely unknown, except in select circles, until the 20th century.
Why was Mendel’s work unappreciated during his time?
There may be several reasons why the significance of Mendel’s work went unrecognized for so many years. One might be tempted to think that the scientists present at his lecture simply were not of the caliber who could appreciate the significance of “the seemingly invariable ratios… with which certain characters had appeared among the hybrids.” As reported in the seminal biography by Hugo Iltis, “The Life of Mendel,” however, on that evening in February 1865, among the 40 members of Mendel’s audience, many were experts in their field.
“….G. von Niessl, the astronomer and botanist. Other members of the audience are Professor Makowsky, the botanist and geologist, Nave, the authority on cryptogams, Dr. Kalmus, another expert in the same branch of research, Theimer the botanist, and Czermak the chemist; all of them are able scientists, helping to give weight to the small audience.” -Hugo Iltis, “The Life of Mendel
After Mendel presented his findings in precise mathematical terms and offered an explanation, there were no questions, and there was no discussion. Rather, the members of the society launched into a discussion of Darwin’s theory of evolution, and no wonder—so entirely did it fill the scientific minds of the time.
A second reason, suggested by Iltis, is that “linking botany with mathematics” may have repelled his audience for a variety of reasons. One of them is that it “may have reminded some of the less expert among them of the mystical numbers of the Pythagoreans.”
Applying mathematics to biology was also an idea well ahead of its time, according to a recent article:
“Additionally, [Mendel’s] use of comparative mathematics to interpret biology was ahead of its time, having important parallels today in the use of computational biology to analyze big datasets.” -”MENDEL: Morphologist and Mathematician Founder of Genetics”
What were the scientific questions of the day?
The underlying and driving question for biologists in Mendel’s time, according to Iltis, was “How is the extraordinary multiplicity of living forms to be explained?” Additionally, there was intense interest in the more specific question of how traits are passed on, and to determine what effect the environment might have on this process.
In a previous post, earlier theories of the evolution of life were presented including ideas central to evolutionary theory: the inheritance of traits, homologous structures, and increasing complexity.
Mendel knew about Darwin
Mendel was not opposed to the theory of evolution. Like many scientists of his day, he bought copies of “Origin” and many other books related to the theory, all of which remain in the monastery library in Brunn. Mendel wrote notes in the margins of the book, and though not opposed to Darwin’s theory, his intuition told him it was somehow inadequate.
Mendel stated that his experiments were actually designed to “support or illustrate the influence of the environment on plants” as suggested by Lamarck’s theory, but his results did not in fact demonstrate this. Rather, in a letter to his friend Carl Nageli, Mendel stated that an organism’s interaction with its environment was not sufficient to significantly change a species:
“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.” -Gregor Mendel
It is known now that environment can play a significant role in the expression or repression of an organism’s genetic make-up over time, but these changes occur through non-Mendelian mechanisms.
Additionally, at the time, it was believed that offspring inherited characteristics by a blending of traits from the parents. Even Darwin offered pangenesis as his theory to explain how this might happen—as pointed out in this article on transgenerational epigenetics.
Did Darwin ignore Mendel’s work?
Mendel had 40 copies printed of his paper, “Experiments in Plant Hybridization,” and may have sent it to Charles Darwin in the hope that his results would contribute to what Mendel perceived as a gap in Darwin’s account (see this video just after the 16-minute-mark). Additionally, it is known that Francis Galton, Darwin’s first cousin, urged Darwin to test Mendel’s laws by growing peas himself.
There is additional evidence that Mendel’s work was mentioned specifically in articles that Darwin consulted for some of his other writings. In fact, in one article, Mendel’s work and results were mentioned 18 times!
So it is possible that Darwin read Mendel’s paper. However, because Darwin had abandoned his theory of pangenes in favor of “survival of the fittest” to explain evolution, it makes some sense that he would have ignored the results from a monk whose major work consisted of one experiment—albeit years long and involving over 27,000 plants.
Other differences between Mendel and Darwin
The differences between Charles Darwin and Gregor Mendel are summarized succinctly in a 2015 paper in Molecular Genetics. Essentially, Darwin wrote an enormous tome meant to convince by sheer volume; Mendel, only 40 pages. Darwin proposed natural selection occurring over millennia; Mendel demonstrated inheritance by artificial selection (hybridization) in “only a few generations.”
Ultimately, Darwin’s theory focused on the variability of species, and Mendel’s results showed a mathematical constancy of inheritable traits. In many respects, the scientific world was not yet ready for Mendel’s ideas. In fact, Mendel’s laws of inheritance and the story of chromosomes, genes, and DNA did not converge until 1944.
In Mendel’s own words:
“It requires indeed some courage to undertake a labor of such far-reaching extent; this appears, however, to be the only right way by which we can finally reach the solution of a question the importance of which cannot be overestimated in connection with the history of the evolution of organic forms.
“The paper now presented records the results of such a detailed experiment.... Whether the plan upon which the separate experiments were conducted and carried out was the best suited to attain the desired end is left to the friendly decision of the reader.” -Gregor Mendel
Indeed, history has made its own decision about Mendel’s pea plant experiments:
And what a legacy for an abbot to bequeath to humanity… a brief 47-page monograph on the progeny of plant hybrids, work conceived and executed over 10 years apparently without preconceived notions, and confined strictly to what we now call phenotypes and the behavior of their formbildenden Elemente in the germ cells. This astonishing epistemological restraint made it so easy for his successors, for example, De Vries, Correns, Tschermak, Bateson… to take the next step to ‘genotype.’ -”MENDEL: Morphologist and Mathematician Founder of Genetics”
But, as suggested in this concluding remark from “The Life of Gregor Johann Mendel: Tragic or Not?” Mendel’s life was not defined by the lack of acceptance of his theory during his lifetime:
“This is the life of Gregor Johann Mendel—reasonably long, kind, charming, great. His was a good heart. His is an imperishable fame.”