Mr. Mivart’s fourth objection seems at least an extremely improbable opinion. He refers to Mr. Darwin’s expression, that the goose appears to have a highly inflexible organization, as if he himself thought it possible for a species at length to attain to an organization completely inflexible. Such a view would imply two parents exactly like one another, producing offspring exactly like themselves; and of such exact likenesses no known families afford examples.
The seventh objection recalls the still unexplained physiological difference between ‘species’ and ‘races,’ unions between the former being sterile, and between the latter fertile. In this branch of the subject there is much scope still for inquiry. Some of the difficulty may be due to a trick played us by language. True species have been defined to be those that are not fertile together; and from the definition it follows that races which are fertile together are not true species. But the question is obscured by the use of the two different words ‘races’ and ‘species,’ the real issue being, whether races that are and races that are not fertile together can originate in the same way. The subject in its other bearings has been largely discussed by Mr. Darwin in his work on ‘Animals and Plants under Domestication.’
It remains only to say a few words on the argument from the calculation of chances which is supposed to reduce the survival by natural selection of any particular useful variation almost or altogether to an arithmetical impossibility. ‘The advantage,’ we are told, ‘whatever it may be, is utterly outbalanced by numerical inferiority. A million creatures are born: ten thousand survive to produce offspring. One of the million has twice as good a chance as any other of surviving: but the chances are fifty to one against the gifted individual’s being one of the hundred survivors. No doubt the chances are twice as great against any one other individual, but this does not prevent their being enormously in favour of some average individual[69].’ In this calculation it seems to be overlooked that every individual will vary more or less, and that out of a million variations there is a very great probability that one should give much more than the amount of advantage which the calculation supposes. Nor does it follow that a variation conferring great advantage in the struggle for life should be great in comparison with a creature’s general organization. There is a very probable alternative, that when the advantages are exceedingly slight they may be shared by a great many, and that when falling to the lot of only one or a few, they may be exceedingly important. The doctrines of reversion and inheritance are pressed into the service of the arithmetical argument to show that the acquired advantage would be gradually diminished and finally lost. But Mr. Darwin tells us that, ‘when a new character appears, it is occasionally from the first well-fixed[70].’ The chances upon one principle that a character will not be transmitted are not worth consideration, if, under the operation of some other principle known or unknown, the transmission of the character actually takes place. We are asked whether one white man, introduced into an island otherwise inhabited only by negroes, would be likely to give the whole island eventually a white, or even a yellow, population. Without trying the experiment, we may perhaps safely answer in the negative. But the illustration loses much or all of its point, when we consider how little the circumstances of the experiment would correspond with what ordinarily happens in nature, how little we know whether the white man’s colour would be really an advantage or the reverse, and how complicated are the differences between a white man and a negro. If the blackness of the negro be due to Natural Selection in any considerable degree, we should expect it to suit the conditions which surround him in his native habitation better than a white skin would do. In this case the pallor introduced into the breed by a solitary stranger would gradually disappear in obedience to the principles of Natural Selection, not in opposition to them. To take once more the instance of the giraffe; the useful variation is here by hypothesis an elongated neck; it is conceivable that out of large herds the few survivors of a drought might be exclusively such as possessed this advantage to some extent. These would probably transmit to a large majority of their descendants the tendency to vary in a given direction which they had themselves all more or less exhibited. Their progeny, moreover, would be placed in exceptionally favourable circumstances by the very fact that in the previous drought so many of the same species had been starved to death, who would otherwise have furnished their chief competitors in the struggle for existence. It is still objected that upon this supposition many other animals ought to have acquired giraffe-like necks. But such an expectation is far from being warranted by the principles of Natural Selection. Since all variations are potentially useful, but only those are preserved which suit the surrounding conditions among which they are exhibited, the calculation of chances will itself plead for the probability that a variety of variations will be preserved, rather than the same many times over. Other species competing with the giraffe for food would be little likely to gain an advantage over it by a slight increase in length of neck, though by other variations they might achieve a decided superiority. It is obvious, also, that the advantage assigned to the elongated neck would belong to many other possible variations, such as a lengthened proboscis, far-reaching arms, the climbing powers of the snake or the monkey, the flight of the bird or the insect; all of which may be due to Natural Selection and the subsidiary principles which the theory of Development embraces.
The calling in of subsidiary principles may be thought to spoil the boasted simplicity of the theory. But such an opinion is hypercritical. One might truthfully say of a great patriot that all he did was in obedience to the simple law of duty, without implying that he was exempt from the law of association of ideas, or independent of the mechanical, chemical, and vital laws which regulate many of the functions of all human beings alike.
FOOTNOTES.
[1] These papers were read at various dates between February 1869 and January 1871, before the Torquay Natural History Society.
[2] Read before the Devonshire Association, July 1870.
[3] Horace, Odes, I. xvi. 13:—
Fertur Prometheus addere principi
Limo coactus particulam undique
Desectam, et insani leonis
Vim stomacho apposuisse nostro.