View this paper (a scan of the original paper as it appeared in the proceedings of the 1899 London Hybrid Conference, which was volume 24 of the society’s journal, published around 1 April 1900)

This paper by William Bateson is an amazing summary of why hybridisation studies were viewed as a major means of investigating evolution (particularly the "species problem"), in the decades following the publication of Origin of Species in 1859, including the time when Mendel performed his studies with crosses between strains of peas. The key point to remember when reading this paper is that it was written, presented and published before Bateson became aware of Mendel's paper.

As Bateson says at the bottom of page 61: "the whole question of the origin of species turns on the relationship of each species or each variety to its nearest allies" [Bateson's italics are also underlined here, for clarity]. It follows that when "varieties are crossed with their nearest allies, we shall have material from which to answer the main questions of which the Species problem consists" (page 62). 

Bateson, who was then a 37-year-old researcher at Cambridge, delivered this paper on 11 July 1899 to the Royal Horticultural Society’s “Hybrid Conference” in London. Comparing the title of Bateson’s paper with the full title of the conference, namely “International Conference on Hybridisation (the Cross-Breeding of Species) and on the Cross-Breeding of Varieties”, indicates the extent to which Bateson’s address was central to the conference. Indeed, the program for the conference shows that Bateson’s paper was the first to be presented, immediately after the Chairman’s introductory remarks. Interestingly, the speaker who followed Bateson was none other than 41-year-old Hugo de Vries, then a professor of plant physiology at the University of Amsterdam, and one of the three re-discoverers of Mendelism! In his paper entitled “Hybridising of monstrosities”, De Vries actually discusses the mysteries of heredity in the context of Darwin’s theory of pangenesis; a subject on which he had just published an entire book.

To return to Bateson’s paper. More than 30 years after Mendel’s paper was published and less than a year before Mendel’s work became known in the English-speaking world, Bateson provides details of the type of hybridisation and cross-breeding experiments that are needed to shed light on evolution. In the most famous passage of this paper, Bateson states:

"We need particular knowledge of the evolution of particular forms. What we first require is to know what happens when a variety is crossed with its nearest allies. If the result is to have a scientific value, it is almost absolutely necessary that the offspring of such crossing should then be examined statistically. It must be recorded how many of the offspring resembled each parent and how many shewed characters intermediate between those of the parents. If the parents differ in several characters, the offspring must be examined statistically, and marshalled, as it is called, in respect of each of those characters separately. Even very rough statistics may be of value. If it can only be noticed that the offspring came, say, half like one parent and half like the other, or that the whole shewed a mixture of parental characters, a few brief notes of this kind may be a most useful guide to the student of evolution." ​​​​[Bateson's italics in the original are here underlined]

It is very telling that this passage begins and ends with mention of evolution. In the following paragraphs, the word "inheritance" is included, but very much in the context of evolution (pages 63 & 64):

"The essential problem of evolution is how any one given step in evolution was accomplished. How did the one form separate from the other? By crossing the two forms together and studying the phenomena of inheritance, as manifested by the cross-bred offspring, we may hope to obtain an important light on the origin of the distinctness of the parents, and the causes which operate to maintain that distinctness.

Useful contributions to the physiology of inheritance . . . can only be got by an exhaustive study of the results of cross-breeding between various forms whose common origin is not very distant. Such experiments must, besides, be repeated sufficiently often to give a fairly extensive series of observations on which to base conclusions. Anyone, therefore, who wishes to work on these lines would do well to restrict himself to an examination of the transmitting properties of a small group of closely allied varieties or species, and to explore these properties thoroughly within that group. 

Cross-breeding, then, is a method of investigating particular cases of evolution one by one". [Bateson's italics in the original are here underlined]

As he was soon to realise, Bateson was describing exactly what Mendel had actually done decades earlier, unbeknown to just about everyone in the English-speaking world.

Not surprisingly, Bateson had already put his own advice into practice: in the last few pages of this paper, he describes hybridisation experiments he and his colleague Edith Saunders had already done, and were doing, with plants. He also mentions plant hybridisations done by de Vries, who had also provided seeds to Bateson. Emphasising the importance of this work, Bateson states (page 65): "There can be no doubt that, tested by the method of breeding and by study of the transmitting powers, the relation of varieties and species would be shewn in an entirely new light."  And on page 66: "I look to the study of cross-breeding to unravel that extraordinary mass of confusion. I look to this method of investigation to deliver us from the eternal debates on the subject of what is specific rank [i.e. what can be classified as a species] and what is not."

On the final page (66), he continues:

"there is such a thing as species, and we have to find out what are the properties of species. 

It is true that, as to most species and varieties, artificial breeding is impossible, but in numerous cases a beginning can be made. Take merely the phenomenon of local varieties, or local species, or local races, about which such weary discussions have arisen. Each of these offers a particular example of the Evolution problem. In numbers of such cases an investigation of the behaviour on crossing could be practiced, and a very few such experiments would, I venture to predict, do more to establish true views of the relation of species and varieties than the labours of systematists will do in ages."

Still in his evolutionary context, Bateson then proceeds to describe the hybridisations he and Saunders have done, and are doing, with chickens:

"To come much nearer home, we do not know for certain the true relationships—in this special sense—between the varieties of the commonest domestic animals and plants. For example, I have been trying to investigate these relationships between the several kinds of comb in domestic poultry. I have thus far found no one who can tell me for certain what happens when they are crossed. The various forms of comb in our breeds of poultry—simple comb, pea-comb, rosecomb, etc.—are important structural features, which differ from each other very much as many natural species do. The answer generally given is that the result of such crossing is uncertain—that sometimes one result occurs, and sometimes another. This, of course, merely means that the problem must be studied on a scale sufficiently large to give a statistical result. There is here an almost untouched ground on which the properties of specific characters can be investigated."

The results of these chicken hybridisations were published from 1902 onwards, and are discussed in separate commentaries below.

Finally, it is worth noting that, as expected, Mendel is not mentioned by de Vries in his paper at the London Hybrid Conference nor in his 1889 book. However, Mendel is actually mentioned by another author in the conference proceedings! On page 187 of the proceedings, in a paper entitled “Hybridisation viewed from the standpoint of systematic botany” by R. Allen Rolfe (an orchid specialist from the Royal Botanic Gardens at Kew), Mendel is mentioned in passing as a known hybridist of Hieracium (hawkweed), without any reference being cited: “F. Schultes and G. Mendel raised several artificially, and at least seven of them I have seen in the dried state.” As is well known, Hieracium are the plant group to which Mendel turned after completing his work on peas. His Hieracium results were published in 1870.

Overall, this paper by Bateson provides very strong evidence, reinforced by the title of Mendel’s 1866 paper (“Experiments in plant hybridization”) and by the mention of Mendel as a hybridist in the 1899 Hybrid Conference, that Mendel was trying to understand hybrids in the context of evolution; he was not searching for the laws of heredity! It must be stressed that this conclusion is completely consistent with the reality that Mendel’s discovery laid the foundation for genetics. It is, however, arguing that Bateson’s paper and the title of Mendel’s paper and the mention of Mendel in the Hybrid Conference proceedings are just three pieces of evidence supporting the idea that Mendel did not set out to make the discovery for which he is now celebrated. For a far more detailed presentation of the evidence supporting this conclusion, see chapter 2 of the book by Shan (2020).

References

De Vries, H. (1899) Intrecellulare Pangenesis. Gustav Fischer, Jena. View this book

de Vries, H. (1900) Hybridising of monstrosities. Journal of the Royal Horticultural Society 24: 69-75. View this paper

Mendel, G. (1870) Ueber einige aus künstlicher Befruchtung gewonnenen Hieracium-Bastarde [On Hieracium hybrids obtained by artificial fertilisation]. Verhandlungen des naturforschenden Vereines in Brünn 49: 48-53. View original version View English version

Rolfe, R.A. (1900) Hybridisation viewed from the standpoint of systematic botany. Journal of the Royal Horticultural Society 24: 69-75. View this paper

Shan, Y. (2020) Doing Integrated History and Philosophy of Science: A Case Study of the Origin of Genetics. Boston Studies in the Philosophy and History of Science, volume 320, Springer, Cham, Switzerland. View this book