| OCR Text |
Show 354 DARWINIAN A. part or phase of that something which directs and de~ termines the expenditure of force, then it is not subject to the laws of the lattor, and there is no ground for inferring its exhaustibility. The limited vitality is an unproved and unprovable conjecture. The evolutive force, dying out in the using, is either the same con~ jecture repeated, or a misapplied analogy. After all-apart from speculative analogies-the only evidences we possess which indicate a tendency in species to die out, are those to which Mr. Darwin has called attention. These are, first, the observed ·deterioration which results, at least in animals, from continued breeding in and in, which may possibly be re·solvable into cumulative heritable diseas·e ; arid, secondly, as already stated (p. 346), what may be termed the sedulous and elaborate pains everywhere taken in Nature to prevent close breeding-arrangements which are particularly prominent in plants, the greater number of which bear hermaphrodite blossoms. The importance of this may be inferred from the universality, variety, and practical perfection of the arrangements which secure the end; and the inference may fairly be drawn that this is the physiological im-port of sexes. , It follows from this that there is a tendency, seem-ingly inherent, in species as in individuals, to die out; but that this tendency is counteracted or checked by sexual ~ider breeding, which is, on the whole, amply secured in Nature, and which in some way or other reenforces vitality to such an extent as to warrant Darwin's inference that "some unknown great good is derived from the union of individuals which have DURATION OF SPECIES. 355 be~n k~?t distinct for many generations." Whether tlus . reenforcement is a complete preventive of decrepitude in species, or only a palliative is more than we can ~eter~ine: If the latter, then e~isting species an~ thmr derwati~es must perish in time, and the eai th may be growmg poorer in species, as M. N audin supposes, ~hro~gh mere senility. If the former, then the .eart~, if not even growing richer, may be expected to hold Its own, and extant species or their derivatives should last as long as the physical world lasts and affords favorable conditions. General analogies seem to favor the ~o~mer view. Such facts as we possess, and the Darwmmn hypothesi~, favor the latter. |
