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This paper was published on 14 January 1903.

It is a review of Mendelian knowledge as it existed at the end of 1902. In addition to strongly endorsing Mendelism, Castle strongly endorses Bateson and Saunders’s explanation of how variation in continuous traits can be due to the segregation of many Mendelian factors, describing the explanation as a “pregnant suggestion”.

Castle starts with an enthusiastic endorsement of Mendelism:

“What will doubtless rank as one of the great discoveries in biology, and in the study of heredity perhaps the greatest, was made by Gregor Mendel, an Austrian monk, in the garden of his cloister, some forty years ago.  . . .  Mendel’s law was rediscovered independently by three different botanists engaged in the study of plant-hybrids —de Vries, Correns, and Tschermak, — in the year 1900.”

Castle then acknowledges the key contribution of Bateson:

“It remained, however, for Bateson, two years later, to point out the full importance and wide applicability of the law. This he has done in two recent publications with an enthusiasm which can hardly fail to prove contagious. There is little danger, I think, of Mendel’s discovery being again forgotten.”

The two Bateson publications cited by Castle are the 1902 volume 1 of the Reports to the Evolution Committee of the Royal Society (see commentaries above) and Bateson’s 1902 book Mendel’s Principles of Heredity: a Defence” (Cambridge University Press, Cambridge). Although this book is very important in the history of Mendelism, there is no separate commentary on it in the PMIA collection because it contains nothing specifically relevant to OMIA species.

Returning to Castle, on page 539 he mentions results of his student Mr G.M. Allen, who obtained the expected Mendelian ratio of grey versus white (meaning albino) in F₂ mice; and who has shown that white/albino mice, being recessive, breed true.

In passing, on page 544, there is a brief mention of results obtained by Castle and Allen confirming that the dancing trait in mice (mentioned as waltzing by Bateson and Saunders (1902; see above) is recessive (and may be associated with reduced viability).

Importantly, in relation to continuous traits, on pages 545-546 Castle states that:

“Bateson [referring to Bateson’s 1902 book and Bateson and Saunders (1902; see above)] makes the pregnant suggestion that even cases of continuous variation may possibly prove conformable with Mendelian principles. Take, for example, the height of peas. It has been found in certain crosses of a tall with a dwarf variety of pea, that the hybrid has an intermediate height. Now, if the hybrid produces pure germ-cells, dwarf and tall respectively, in equal numbers, the next generation will consist of three classes of individuals, dwarf, intermediate, and tall, in the proportions, 1 : 2 : 1. But if each of the original characters should undergo disintegration, we might get a dozen classes, instead of three, resulting in a practically continuous frequency-of-error curve.” 

Bateson’s 1902 book includes (on pages 31 and 32) a similar explanation as in the other Bateson reference mentioned by Castle (volume 1 of Reports), of how variation in continuous traits can be due to the segregation of many Mendelian factors:

“In the case of a population presenting continuous variation in regard to say, stature, it is easy to see how purity of the gametes in respect of any intensities of that character might not in ordinary circumstances be capable of detection. There are doubtless more than two pure gametic forms of this character, but there may quite conceivably be six or eight. When it is remembered that each heterozygous combination of any two may have its own appropriate stature, and that such a character is distinctly dependent on external conditions, the mere fact that the observed curves of stature give " chance distributions" is not surprising and may still be compatible with purity of gametes in respect of certain pure types.”

So, we now have direct evidence that on both sides of the Atlantic, the multufactorial conceptual solution to the biometrical/Mendelian controversary was recognised as early as 1902!

As mentioned in the earlier commentary on Bateson and Saunders (1902; Part III), it remains a mystery as to why neither Fisher (1918) nor Yule (1902) acknowledged Bateson; and now we can add Castle (1903) as well.

References

Bateson, W. (1902) Mendel’s Principles of Heredity: a Defence. Cambridge University Press, Cambridge. View this book

Bateson, W., Saunders, E.R. (1902) Reports to the Evolution Committee of the Royal Society 1: 1-160. View this volume