Now, with regard to these instances of early specialization, as also with regard to the changed estimate of the degrees of affinity between forms, it is not pretended for a moment that such facts are irreconcilable with "Natural Selection." Nevertheless, they point in an opposite direction. Of course not only is it conceivable that certain antique types arrived at a high degree of specialization and then disappeared; but it is manifest they did do so. Still the fact of this early degree of excessive specialization tells to a certain, however small, extent against a progress through excessively minute steps, whether fortuitous or not; as also does the distinctness of forms formerly supposed to constitute connecting links. For, it must not be forgotten, that if species have manifested themselves generally by gradual and minute modifications, then the absence, not in one but in all cases, of such connecting links, is a phenomenon which remains to be accounted for.
It appears then that, apart from fortuitous changes, there are certain difficulties in the way of accepting extremely minute modifications of any kind, although these difficulties may not be insuperable. Something, at all events, is to be
said in favour of the opinion that sudden and appreciable changes have from time to time occurred, however they may have been induced. Marked races have undoubtedly so arisen (some striking instances having been here recorded), and it is at least conceivable that such may be the mode of specific manifestation generally, the possible conditions as to which will be considered in a later chapter.
CHAPTER V.
AS TO SPECIFIC STABILITY.
What is meant by the phrase "specific stability;" such stability to be expected a priori, or else considerable changes at once.—Rapidly increasing difficulty of intensifying race characters; alleged causes of this phenomenon; probably an internal cause co-operates.—A certain definiteness in variations.—Mr. Darwin admits the principle of specific stability in certain cases of unequal variability.—The goose.—The peacock.—The guinea fowl.—Exceptional causes of variation under domestication.—Alleged tendency to reversion.—Instances.—Sterility of hybrids.—Prepotency of pollen of same species, but of different race.—Mortality in young gallinaceous hybrids.—A bar to intermixture exists somewhere.—Guinea-pigs.—Summary and conclusion.
As was observed in the preceding chapters, arguments may yet be advanced in favour of the opinion that species are stable (at least in the intervals of their comparatively sudden successive manifestations); that the organic world consists, according to Mr. Galton's before-mentioned conception, of many facetted spheroids, each of which can repose upon any one facet, but, when too much disturbed, rolls over till it finds repose in stable equilibrium upon another and distinct facet. Something, it is here contended, may be urged, in favour of the existence of such facets—of such intermitting conditions of stable equilibrium.
A view as to the stability of species, in the intervals of change, has been well expressed in an able article, before quoted from, as follows:[[104]]—"A given animal or plant appears to be