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Show 48 RECAPITULATION. [Ch. III. sile tails of some A men·c an mon k eys. Instead of beinOo' red uce d to t h e necess1' ty of subiJ u~oT ating stubborn and untract. - able brutes, we should naturally have anticipated " that. thetr wants would have excited them to efforts, and that contmued efforts would have given rise to new organs;" or~ rather, .to the re-acqms. 1.t 1.0 n o f 01 .g .a ns which , in a manner trreconCIIcable with the principle of the p'rog-ressive system, have grown. obsolete in tribes of men which have such constant need of them. , It follows, then, from the different facts which we have con-sidered in this chapter, that a short period of ~ime is gener~lly sufficient to effect nearly the whole change wh1ch an alteration of external circumstances can bring about in the habits of a species, and that such capacity of accommodation to n~w circumstances is enjoyed in very different degrees by different species. Certain qualities appear to be bestowed e~clusively wit~ a view to the relations which are destined to exist between (hfferent species, and, among others, between certain species and man; but these latter are always so nearly connected with the original habits and propensities of each species in a wild stat~, that they imply no indefinite capacity of varying from th: ~nginal type. The acquired habits, derived from hu~an tUitiOn, are rarely transmitted to the offspring; and when th1s ~1appens, it is almost universally the case with those merely whiCh have some obvious connexion with the attributes of the species when in a state of independence. CHAPTER IV. Consideration of the question whether species have a real existence in nature, continued-Phenomena of hybrids-Hunter's opinions as to mule animalsMules not strictly intermecliate between the parent species-Hybrid plantsExperiments of Kolreuter-The same repeated by Wiegmann-Vegr.table hybrids prolific throughout several generations-Why so rare in a wild stateDccandolle's opinion respecting hybrid plants-The phenomena of hybrids confirms the doctrine of the permanent distinctness of species-Theory of the gradation in the intelligence of animals as indicated by the facial angle-Dis. covery of Tieddemann that the brain of the footus in mammalia assumes succes4 sively the form of the brain of a fish, reptile, and bird-Bearing of this discovery 011 the theory of progressive development and transmutation-Recapitulation. WE have yet to consider another class of phenomena, those relating to the production of hybrids, which have been regarded in a very different light with reference to their bearing on the question of the permanent distinctness of species; some naturalists considering them as affording the strongest of all proofs in favour of the reality of species; others, on the contrary, appealing to them as countenancing the opposite doctrine, that all the varieties of organization and instinct now exhibited in the animal and vegetable kingdoms, may have been propagated from a small number of original types. In regard to the mammifers and birds, it is found that no sexual union will take place between races which are remote from each other in their habits and organization ; and it is only in species that are very nearly allied that such unions produce offspring. It may be laid down as a general rule, admitting of very few exceptions among quadrupeds, that the hybrid progeny is steril, and there seem to be no well-authenticated ex~mples of the continuance of the mule race beyond one generatiOn. The principal number of observations and experiments relate to the mixed offspring of the horse and the ass; and in this case it is well established, that the male-mule can generate and the female-mule produce. Such cases occur in Spain and Vot.. II. E |
