Abstract
IN this, the first part of a paper on reversion, the two following questions are dealt with, viz.: (1) Is there invariably evidence of reversion? (2) May reversion, when it does occur, result in the complete, or all but complete restoration of either comparatively recent or of comparatively remote ancestors? The first question is answered in the negative, but to the second an affirmative answer is given. In support of the view that reversion does not invariably occur, it is pointed out (1) that clear evidence of reversion is rare in the pure-bred offspring of highly prepotent animals, such as Galloway, Aberdeen, Angus, and Shorthorn cattle. And (2) that there is sometimes no evidence of reversion in cross-bred animals. While it is deemed unnecessary to submit evidence of the fact, long recognised by breeders, that the offspring of highly prepotent animals are, as a rule, the image of their parents, it is thought desirable to submit evidence in support of the contention that in cross-bred animals indications of reversion may be wholly wanting. The following experiments bear on this point: (a) When a prepotent Galloway bull (which is black and hornless) is crossed with a Highland heifer, the result maybe an animal which experts are unable to distinguish from a pure-bred Galloway—there may be neither a trace of the long-horned Highland parent, nor yet any indication of reversion. (b) A peculiarly marked skewbald (bay and white) Iceland pony mare, when mated with a whole-coloured bay Shetland pony, produced a foal which in colour, form, and gait is almost identical with the skewbald dam—on no single point does it suggest the bay Shetland sire, (c) A nearly black Shetland mare, when mated with a bay Welsh pony, produced a bay foal which in its make, colour, &c., is the image of the sire, (d) A pure white fantail pigeon, crossed with a blue pouter hen, yielded a nearly white bird having the form and habits of a pouter, but no suggestion of Columba livia, the supposed ancestor of the numerous varieties of pigeons. (e) A white Shorthorn crossed with Aberdeen, Angus, or Galloway cattle results in “blue-greys,” which, though more or less intermediate in their Characters, rarely afford any evidence of reversion. It thus appears that, notwithstanding the “swamping effects of intercrossing,” the offspring of quite distinct varieties sometimes afford no evidence of reversion, and, further, that Galton's law of heredity (which teaches that the intermediate and remote ancestors together contribute one-half of the total heritage of the average offspring) does not appear to hold in the case of highly prepotent animals. In dealing with the second question, experiments are first described in support of the view that there may be complete, or all but complete, reversion to comparatively recent ancestors. (a) A blue and white fantail (a cross between a white fantail and a dark blue cross-bred fantail), when mated with a blue fantail, invariably produces pure white fantails, identical, as far as external characters go, with their grandsire. (b) A smooth-coated white rabbit (a cross between an Angora and a smooth-coated white buck), mated with a smooth-coated and almost white doe (the granddaughter of a Himalaya rabbit), produced a litter of three, one of which is the image of the mother, one is an Angora like the grandmother, while the third is a Himalaya (with the characteristic black ears and muzzle and dark grey feet and tail) like the great grandmother.
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By Prof. J. C. Ewart, F.R.S. (Communicated to the Royal Society of Edinburgh, December 5, 1898).
"Animals and Plants," vol. i. p. 210.
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Experimental Contributions to the Theory of Heredity1. Nature 59, 354–355 (1899). https://doi.org/10.1038/059354a0
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DOI: https://doi.org/10.1038/059354a0