very much less for them than races that have had little or no experience of them. Between narcotics in relation to which the individual is able with ease to vary greatly—e.g. tobacco—and narcotics in relation to which the individual is able to vary comparatively little—e.g. alcohol—lie the other narcotics, some of which resemble tobacco in the ease with which the individual is able to undergo protective reaction against them, and others alcohol in the absence of the power of making, to any great extent, such protective reaction. As in the case of diseases, the worst, the most death-dealing, of narcotics are those against which the race is protected almost solely by the inborn power of making immediate resistance; a power which arises in the race only through a very tedious process of evolution, the result of a prolonged and stringent process of selection.
Except as regards alcohol and opium, we have little or no evidence to assist us in forming an estimate of the extent of the evolution caused in various races by the use of deadly narcotics. We can estimate its extent in different cases only by comparing races which have been long and disastrously familiar with this or that narcotic, with races which have had little or no experience of them; and save in the case of the two narcotics named, I do not know that anything has been published in which such comparisons are instituted—possibly for the reason that no races previously unfamiliar with them have recently acquired the habit of using them. I confess, however, that I have not very diligently sought evidence bearing on the matter, being convinced that it is a foregone conclusion, that wherever any narcotic has for a lengthened period been the cause of a considerable elimination of the unfit in relation to it, it has also, like virulent zymotic disease, like alcohol, like opium (as we shall see), been the cause of a considerable evolution protective against itself.
