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Show 240 DARWINIAN A. resclted in species and that which is exhibited in races and minor varieties. And now in the introductory chapter of the vol-ume of essay~ before us, he informs us that the idea which pervades them all, and in ~om~· sort. con~ec~s very diverse topics, is that o~ c~nsid~rmg this prmClple of selection. Of the pnnCiple Itself, ~e remarks that it is neither a theory nor an hypothesis, but the expression of a necessary fact ; that to d~ny it is very much like denying that round stones will roll downhill faster and farther than flat ones ; and that the question of. the present day in ~atural history is not whether there be natural selectwn, or even whether forms are derived from other forms, but to comprehend how, in what proportions, and by what means hereditary deviations take place, and in what ways an inevitable selection takes effect upon these. In two of these essays natural selection is directly discussed . in its application to the human race; the larger one dealing ably with the whole subject, and with res~lts at first view seemingly in a great degree negative, but yet showing that the supposed" failure of natural selection in the case of man" was an unwarrantable conclusion from too limited a view of a very complicated question. The article abounds in acute and fertile suggestions, and its closing chapter, "on the probable future of the human species" under the laws of selection, is highly interesting and no~ewort?Y· The other and shorter essay discusses a special pomt, and brings out . a corollary of the law of heredity which may not have been thought of before, but which is perfectly clear as soon as it is stated. It ex- ATTITUDE OF WORKING NATURALISTS. 241 plainsf at once why contagious or epi'd ern1.c dI' seases are most atal at their first appearance, and less Eo after- ":ard: not by the dying out of a virus-for, when the disease reache•s a new populac tion , I. t I.s as vn. -u 1e nt as e;er (as, for mstance, th.e small-pox among the In-dmns)- but by the selectwn of a race less subject to attack through the destruction of tho se th at were m.o re so, and th. e inheritance of the com parat I' ve I. mrnu-m. ty by thed c hildren and the grandchildren of the sur- VIvo:s; an . how this immunity itself, causing the particular disease. .t o become rare, pav es th e way to a return o• f the onmo~n al fatality ,. for the mass of sue h pop.u laat· iOn, both i.n the present and the I·In me dJ' a t e1 y . ?rece .mg generatiOn, not having been exposed to the 1m fe·c twn, or bu.t li.t tle exposed ' has not und ergone se-ectwn, and so m time the proportion liable to attack, or to fatal attack, gets to be as large as ever. The great.er t1.e fatality, especially in the population under mamag~able age, the more favorable the condition of the survivors; and, by the law of heredity, their children should share in the immunity. This explanation ?f the cause, or of one cause, of the return of pests at mtervals no less applies to the diminution of the efficacy. of .remedies, and of preventive means, such as vaccmatwn. When Jenner introduced vaccination the small-pox in Europe and European colonies. mus~ h~ve lost somewhat of its primitive intensityby the VIgorous wee~ing out of the more susc~ptible through many generatwns. Upon the residue, vaccination was a!most complete protection, and, being generally practised, small-pox consequently became rare. Selection thus ceasing to operate, a population arises which has |