Heredity / by J. Arthur Thomson.

  • John Arthur Thomson
Date:
1920
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Heredity / by J. Arthur Thomson. Source: Wellcome Collection.

    157/692 (page 121)
    ILLUSTRATIONS 121 taken as serious pieces of evidence in favour of the reversion theory, but they may serve to hint at the readiness with which the hypo¬ thesis of characters lying latent has been adopted. As we shall see, reversions in the strict sense are apparently few and far be¬ tween. A foal is sometimes born with a few stripes on its fore-legs, as if reminding us of striped wild horses. A dovecot with carefully bred pigeons was left to itself for some years, after which it was found to contain numerous blue pigeons, resem¬ bling in many ways the wild rock-dove (Columba livia). A Fig. 25.—Devonshire pony, shoAving the occurrence of stripes. (From Darwin. ) dark-coloured child may be born in a family where there has been some Eurasian mixture. Cultivated flowers and vegetables, such as pansies and cabbages, sometimes produce forms hardly distinguishable from their wild progenitors. The nectarine derived from a peach may produce what is practically a peach again. The white-flowering currant—derived from the common red form—may have branches with red flowers. These are preliminary illustrations of what are usually called reversions—the hypothesis implied being that they are returns, or throw-backs, to an ancestral type. § 2. Suggested Definitions Darwin's introductory exposition (1868, vol. ii. p. 28) was as follows : When the child resembles either grandparent more