[42] Nature, vol. xliii. pp. 410, 557; vol. xliv. pp. 7, 29. I say "adopted," because I had objected to his quoting the analogy of artificial selection, and stated, as above, that the only way to meet Mr. Spencer's "difficulty" was to deny the fact of co-adaptation as ever occurring in any case. It then appeared that Professor Meldola agreed with me as to this. But I do not yet understand why, if such were his view, he began by endorsing Mr. Wallace's analogy from artificial selection—i. e. confusing the case of co-adaptation with that of the blending of adaptations. If any one denies the fact of co-adaptation, he cannot assist his denial by arguing the totally different fact that adaptations may be blended by free intercrossing; for this latter fact has never been questioned, and has nothing to do with the one which he engaged in disputing.
[43] It may be said, with regard to this particular reflex, that it may perhaps be, so to speak, a mechanical accident, arising from the contiguity of the sensory and motor roots in the cord. But as this suggestion cannot apply to other reflexes presently to be adduced, it need not be considered.
[44] Of course it will be observed that the question is not with regard to the development of all the nerves and muscles concerned in this particular process. It is as to the development of the co-ordinating centres, which thus so delicately respond to the special stimuli furnished by variations of angle to the horizon. And it is as inconceivable in this case of reflex action, as it is in almost every other case of reflex action, that the highly specialized machinery required for performing the adaptive function can ever have had its origin in the performance of any other function. Indeed, a noticeable peculiarity of reflex mechanisms as a class is the highly specialized character of the functions which their highly organized structures subserve.
[45] We meet with a closely analogous reflex mechanism in brainless vertebrata of other kinds; but these do not furnish such good test cases, because the possibility of natural selection cannot be so efficiently attenuated. The perching of brainless birds, for instance, at once refers us to the roosting of sleeping birds, where the reflex mechanism concerned is clearly of high adaptive value. Therefore such a case is not available as a test, although the probability is that birds have inherited their balancing mechanisms from their sauropsidian ancestors, where it would have been of no such adaptive importance.
[46] Pflüger's Archiv, Bd. xx. s. 23 (1879).
[47] Brain, part xlviii, pp. 516-19 (1889).—There is still better proof of this in the case of certain rodents. For instance, observing that rats and mice are under the necessity of very frequently scratching themselves with their hind-feet, I tried the experiment of removing the latter from newly-born individuals—i.e. before the animals were able to co-ordinate their movements, and therefore before they had ever even attempted to scratch themselves. Notwithstanding that they were thus destitute of individual experience with regard to the benefit of scratching, they began their scratching movements with their stumps as soon as they were capable of executing co-ordinated movements, and afterwards continued to do so till the end of their lives with as much vigour and frequency as unmutilated animals. Although the stumps could not reach the seats of irritation which were bent towards them, they used to move rapidly in the air for a time sufficient to have given the itching part a good scratch, had the feet been present—after which the animals would resume their sundry other avocations with apparent satisfaction. These facts showed the hereditary response to irritation by parasites to be so strong, that even a whole life-time's experience of its futility made no difference in the frequency or the vigour thereof.
[48] For details of his explanation of this particular case, for which I particularly inquired, see Mental Evolution in Animals, pp. 301-2.
[50] For fuller treatment see Mental Evolution in Animals, pp. 274-285, 378-379, 381-383.
[51] For an excellent essay on the deleterious character of early forms of religion from a biological point of view, see the Hon. Lady Welby, An Apparent Paradox in Mental Evolution (Journ. Anthrop. Inst. May 1891).