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Show 350 JJARWINIANA. fundamental law of inheritance ; ·but the speeies, like the individual, loses .plasticity and vital force. To continue in the language of the original: " C'est dire qu'il y a eu, pour !'ensemble . du monde organique, nne periode de formatio~ ou tout etai~ chan~ean~ et mobile une phase analogue ala v1e embryonnan·e eta la Jeunesse de ~haque ~tre particulier; et qu'a cet Age de mobilite et de croissance a succede une periode de stabilite, au moins relative, une sorte d'Age adulte, ou la force evolutive, ayant acheve son reuvre, n'est plus occupee qu'a la maintenir, sans pouvoir produire d'organismes nouveaux. Limitee en quantite, comme toutes los forces en jeu dans une planete ou dans un systeme sideral tout entier, cette force n'a pu accomplir qu'un travail limite ; et du m~me qu'un organisme, animal ou ve~etal, , no croit pas indefiniment et qu'il s'arr€lte a des proportwns que rien ne pout faire depasser, de m€lme aussi l'organisme total de la nature s'est arr€lte a un etat d'equilibre, .dont la duree, selon toutes vraisemblances, doit ~tre beaucoup plus longue quo cello de la phase de developpement et de croissance. A fixed amount of "evolutive force" is given, to begin with. At first enormous, because none has been used up in work, it is necessarily enfeebled in the currents into which the stream divides, and the narrower and narrower channels in which it flows with slowly-diminishing power. Hence the limited although very unequal duration of a~l i~dividuals, of all species, and of all types of orgamzatwn. A multitude of forms have disappeared already, and tho number of species, far from increasing,.as some h~vo believed must on the contrary, be diminishing. Some species n' o dou' bt have suffered death by v1.0 1e nce or acciden' t, by geolo' gical changes, local alteratiO. n. of t h c conditions, or the direct or indirect attacks of other DURATION OF SPECIES. 351 species ; but these have only anticipated their fate, for M. Naudin contends that most of the extinct . species have died a natural death from exhaustion of force, and that all the surviv-ors are on the way to it. The great timepiece of Nature was wound up at the beginning, and is running down. In the earlier stages of great plasticity and exuberant power, diversification took place freely, but only in definite lines, and species and types multiplied. As the power of survival is inherently limited, still more the power of change: this. diminishes in time, if we rightly apprehend the idea, partly through the waning of vital force, partly through the fixity acquired by heredity -like producing like, the more certainly in proportion to ~he length and continuity of the ancestral chain. And so the small variations of species which we behold are the feeble remnants of the pristine plastie;ity and an exhausted force.1 This force of variation or origination of forms has acte<;I rhythmically or intermittently, because each movenient was the result of the rupture of an equilibrium, the liber- 1 In noticing M. N au din's paper in the Oomptes Rend·us, now reprinted in the" A.nnales des Sciences Naturelles," entitled" Yal'iation dosordonnee des Plantes Hybrldes et Deductions qu'on peut en tirer," we were at a loss to conceive why he attributed all present variation of species to atavism, i. e., to the reappearance of ancestral characters (American Journal of Science, February, 1876). His anterior paper was not then known to us ; from which it now appears that this view comes in as a part of the hypothesis of extreme plasticity and variability at the fit·st, subsiding at length into entire fixity and persistence of character. .According to which, it is assumed that the species of our time have lost all power of original variation, but can still reproduce some old ones-some reminiscences, as it were, of youthful vagariesin the way of atavism. |
