[23] Possibly the school of Weismann may simply refuse to accept the facts, which are confessedly rare, and, in many of the cases alleged, dubious. In other cases, however, the evidence is sufficient to have satisfied the cautious judgement of Darwin, who has discussed it in detail. Therefore, even if the Neo-Darwinians repudiate this evidence, at least they ought to state that such is the position which they adopt.
[24] Nature, Feb. 6th, 1890.
[25] Nature, vol. xl. p. 626.
[26] Ibid., vol. xli. p. 322.
[27] In his Essays (vol. i. p. 282) Weismann says:—“If it could be shown that a purely parthenogenetic species had become transformed into a new one, such an observation would prove the existence of some new force of transformation other than selective processes, for the new species could not have been produced by these latter.” But now it has been shown that a purely parthenogenetic species can be transformed into a new one, and therefore it seems desirable to note that the observation does not so much as tend to prove the existence of some new force of transformation other than selective processes. For this most singular statement can only stand on a prior acceptance of Weismann’s own assumption, as to amphigony being the only possible cause of individual hereditary variation. Only if we have already, and with absolute certainty, embraced the whole Weismannian creed, could we consent to affirm that “natural selection is an impossibility in a species propagated by a-sexual reproduction.”
[28] What he says is:—“It was only after a greater or less number of generations had elapsed that a variable proportion of double flowers appeared, sometimes accompanied by changes in the leaves and in the colours of the flowers. This fact admits of only one interpretation:—the changed conditions at first produced slight and ineffectual changes in the idio-plasm of the individual, which was transmitted to the following generation.... Now, the idio-plasm of the first ontogenetic grade (viz., germ-plasm) alone passes from one generation to another, and hence it is clear that the germ-plasm itself must have been gradually changed by the conditions of life, until the alteration became sufficient to produce changes in the soma, which appeared as visible characters in either flower or leaf.”—Essays, pp. 426-7; italics mine.
[29] Nature, Nov. 14, 1889, p. 41.
[30] Essays, 2nd Ed., pp. 331-2.
[31] Essays, p. 296.
[32] In this connexion it ought to be observed that Darwin believed the causes of variation to be internal as well as external—or arising from “the nature of the organism” no less—or even more—than from “changed conditions of life.” But although he appears to have entertained the admixture of hereditary endowments in sexual unions as one of the causes of variation belonging to the former category, he expressly says that he did not regard it as the only, or even the main, cause. (See Variation, &c., vol. i, pp. 197, 398; vol. ii, pp. 237, 252.)