Artificial selection could be perfectly applied to the human species, in which case marriages would be arranged between persons better endowed, physically and mentally, and the worse endowed would be excluded from marriage. But this selection encounters the gravest practical difficulties; because, if it is relatively easy to estimate the physical qualities of man, nothing on the other hand is harder than to estimate his mental qualities. A dynamometer of intelligence does not exist, and Galton's method of observing the points of merit of University graduates is very insufficient and fallible. In face of these difficulties there naturally arises the idea of inferring the psycho-physical aptitudes of individuals from their social and economic position, or from their income, which is easily measured. In accord with this idea, it would be a question of acting so that marriages would be effected exclusively and predominantly amongst individuals provided with superior incomes, and to prevent, as far as possible, marriages between persons of inferior incomes, or of no income at all. But all this would be plausible if there should be a real analogy between the economic élite, and the psycho-physical élite, or if the former were really a product of the latter. Now, this is precisely what I deny. The _economic élite_ is not in the least the product of the possession of superior qualities, but is simply the result of a blind struggle between incomes, which carries to the top those who, at the start, possess a larger income through causes which may be absolutely independent of the possession of superior endowments. (See my _Sintesi economica_--Paris, Giard et Briard, 1911.) Hence, nothing makes it impossible that the wealthier people should be precisely the worst endowed, physically and mentally, and this as a matter of fact happens in innumerable cases. Besides, we have an indirect proof of this in the very results of selective processes as, until now, they are practised. And, in fact, conjugal selection to-day takes place precisely amongst individuals of the same class, or belonging to the same standard of income, so that persons of the upper classes always marry exclusively amongst each other. So then these marriages, which, according to the theory, ought to give more splendid results, give, on the contrary, more wretched results. Galton's same law of "return to the mean," or the fact that the descendants of persons of high class sometimes have inferior endowments as compared with the average of the race, could not be fulfilled if persons of the upper classes who marry with each other were really select persons, physically and mentally.