segunda-feira, 7 de maio de 2012

Did Darwin read Mendel?

David Galton

    The Mendel-Darwin Connection - Michael Ruse

    Read no further if you want a definite answer to this question. It is a sort of detective story with clues scattered around. The circumstances surrounding the question however are so interesting since they involve two of the most important scientific publications of the 19th century.

    The truly ground-breaking studies of Gregor Mendel were read before the Society for the Study of Natural Science of Brunn in 1865 entitled Versuche uber Pflanzen-Hybriden (Experiments in Plant Hybridization). Mendel ordered 40 reprints of his paper to send to famous European scientists; Darwin by then was certainly one of the most famous. Darwin's book on Origin of Species had been out for 6 years and was already in its 3rd edition. It had been translated into German, French, Dutch, Spanish, Polish and Russian.

    Mendel had of course read and studied the Origin of Species in the German translation, Uber die Entstehung der Arten as soon as the second edition appeared in 1863. In his personal copy, he made many notes in the margin with his small and careful handwriting with double underlines of some of the text and even interspersed with the occasional exclamation mark. He bought most of Darwin's other works and studied them carefully making frequent annotations. So it would be natural for him to send Darwin, as an eminent English naturalist, one of his 40 reprints.

    Of the 40 reprints of Mendel's article records exist that one was sent to each of the following scientists: von Marilaun, Kerner, Beijerinck, Boveri, Schleiden, and the Swiss botanist Karl Wilhelm von Nageli, now working in Munich. The last exchanged letters with Mendel over 7 years on the topic. More copies of the reprint were to be found in learned societies around Europe including the Royal Society, the Linnaean Society and the Greenwich Observatory in Britain.

    Where were the other remaining reprints sent (about 29)? At the time Darwin's house in Kent was a sort of communication hub for European naturalists. Darwin was writing (and receiving) letters on a daily basis about issues and problems of natural history. If Darwin had received and read Mendel's article, he would have found a detailed analysis of the frequencies observed for different inherited traits from generation to generation of the edible pea. But these results were given in a mathematical form that might have put Darwin off from reading any more of the article. Darwin said that: ‘Mathematics in biology was like a scalpel in a carpenter's shop – there was no use for it.’ The concluding remarks of the paper made quite far reaching claims that the author had discovered laws that could predict the appearance of the different hybrid characters in successive generations of the edible pea, and that this would probably apply to other plant species. Of course it needed confirmation by further experimentation, but in view of the unity in the developmental plan of all organic life one may assume it to be correct. The final two paragraphs argued that the transference of characteristics amongst cultivated plants, such as the edible pea, can be accomplished and seems to occur by discrete integral steps which if accumulating in one species of plant could ‘transform’ it into a different species. Mendel's conclusions left no room for blending inheritance that Darwin believed to occur.