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 {112} 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. [Page 113] * * * * * 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.