Darwin only published one account of his provisional hypothesis of pangenesis, and that is to be found in chapter xxvii of his bookThe Variation of Animals and Plants under Domestication, the first edition of which is dated 1868. The absence of any earlier account in Darwin's works has led some to assume that he had recourse to this hypothesis only a short time before the published date of the book containing it, and on the basis of this assumption they have (...) asserted that he produced it as a part of his defence of the theory of evolution against the criticisms made of it by the physicists Sir William Thomson, afterwards Lord Kelvin, and Fleeming Jenkin. But to make such an assertion is to ignore the fact that Darwin had already sent his manuscript of pangenesis to Huxley in the year 1865, two years before Fleeming Jenkin's article appeared and three years before Lord Kelvin openly attacked the evolutionary theory. The discovery of this manuscript of pangenesis has, therefore, some importance, for it should reveal Darwin's conception of pangenesis in 1865. (shrink)

Hugo de Vries claimed that he had discovered Mendel's laws before he found Mendel's paper. De Vries's first ratios, published in 1897, for the second generation of hybrids were 2/3:1/3 and 80%:20%. By 1900, both of these ratios had become 3:1. These changing ratios suggest that as late as 1897 de Vries had not discovered the laws, although he asserted, from 1900 on, that he had found the laws in 1896. An Appendix details de Vries's Mendelian experiments as described in (...) the original edition of volume two of Die Mutationstheorie, but omitted entirely from the English translation. (shrink)

It is argued that de Vries did not see Mendel's paper until 1900, and that, while his own theory of inheritance may have incorporated the notion of independent units, this pre-Mendelian formulation was not the same as Mendel's since it did not apply to paired hereditary units. Moreover, the way in which the term ‘segregation’ has been applied in the secondary literature has blurred the distinction between what is explained and the law which facilitates explanation.