Were some hitherto unknown bird, driven by stress of weather from theremote north, to make its appearance on our shores, it would excite no speculationin the sheep or cattle amid which it alighted: a perception of it as a creaturelike those constantly flying about, would be the sole interruption of thatdull current of consciousness which accompanies grazing and rumination. Thecowherd, by whom we may suppose the exhausted bird to be presently caught,would probably gaze at it with some slight curiosity, as being unlike anyhe had before seen would note its most conspicuous markings, and vaguelyponder on the questions, where it came from, and how it came. By the sightof it, the village bird-stuffer would have suggested to him sundry formsto which it bore a little resemblance; would receive from it more numerousand more specific impressions respecting structure and plumage; would bereminded of other birds brought by storms from foreign parts; would tellwho found them, who stuffed them, who bought them. Supposing the unknownbird taken to a naturalist of the old school, interested only in externals,(one of those described by Edward Forbes, as examining animals as thoughthey were skins filled with straw,) it would excite in him a more involvedseries of mental changes. There would be an elaborate examination of thefeathers, a noting of all their technical distinctions, with a reductionof these perceptions to certain equivalent written symbols; reasons for referringthe new form to a particular family order, and genus would be sought outand written down; communications with the secretary of some society or editorof some journal, would follow; and probably there would be not a few thoughtsabout the addition of the ii to the describer's name, to form the name ofthe species. Lastly, in the comparative anatomist such a new species, shouldit have any marked internal peculiarity, might produce additional sets ofchanges -- might suggest modified views respecting the relationships of thedivision to which it belonged; or, perhaps, alter his conceptions of thehomologies and developments of certain organs; and the conclusions drawnmight possibly enter as elements into still wider inquiries concerning theorigin of organic forms.
From ideas let us turn to emotions. In a young child, a father's angerproduces little else than vague fear -- a sense of impending evil, takingvarious shapes of physical suffering or deprivation of pleasures. In elderchildren the same harsh words will arouse additional feelings: sometimesa sense of shame, of penitence, or of sorrow for having offended; at othertimes, a sense of injustice and a consequent anger. In the wife, yet a furtherrange of feelings may come into existence -- perhaps wounded affection, perhapsself-pity for ill-usage, perhaps contempt for groundless irritability, perhapssympathy for some suffering which the irritability indicates, perhaps anxietyabout an unknown misfortune which she thinks has produced it. Nor are wewithout evidence that among adults, the like differences of development areaccompanied by like differences in the number of emotions aroused, in combinationor rapid succession: the lower natures being characterized by that impulsivenesswhich results from the uncontrolled action of a few feelings; and the highernatures being characterized by the simultaneous action of many secondaryfeelings, modifying those first awakened.
Perhaps it will be objected that the illustrations here given, are drawnfrom the functional changes of the nervous system, not from its structuralchanges; and that what is proved among the first does not necessarily holdamong the last. This must be admitted. Those, however, who recognize thetruth that the structural changes are the slowly accumulated results of thefunctional changes, will readily draw the corollary that a part-cause ofthe evolution of the nervous system, as of other evolution, is this multiplicationof effects which becomes ever greater as the development becomes higher. §161. If the advance of Man towards greater heterogeneity, in bothbody and mind, is in part traceable to the production of many effects byone cause, still more clearly may the advance of Society towards greaterheterogeneity be so explained.
Consider the growth of industrial organization. When some individual ofa tribe displays unusual aptitude for making weapons, which were before madeby each man for himself, there arises a tendency towards the differentiationof that individual into a maker of weapons. His companions, warriors andhunters all of them, severally wishing to have the best weapons that canbe made, are certain to offer strong inducements to this skilled individualto make weapons for them. He, on the other hand, having both an unusual faculty,and an unusual liking, for making weapons (capacity and desire being commonlyassociated), is predisposed to fulfil these commissions on the offer of adequaterewards: especially as his love of distinction is also gratified. This firstspecialization of function, once commenced, tends ever to become more decided.
On the side of the weapon-maker, continued practice gives increased skill.
On the side of his clients, cessation of practice entails decreased skill.
Thus this social movement tends to become more decided in the direction inwhich it was first set up; and the incipient heterogeneity is, on the averageof cases, likely to become permanent for that generation, if no longer.
Such a differentiation has a tendency to initiate other differentiations.
