Page:Principles of Political Economy Vol 1.djvu/219

Rh Twenty or thirty years ago, these propositions might still have required considerable enforcement and illustration; but the evidence of them is so ample and incontestable, that they have made their way against all kinds of opposition, and may now be regarded as axiomatic: though the extreme reluctance felt to admitting them, every now and then gives birth to some ephemeral theory, speedily forgotten, of a different law of increase in different circumstances, through a providential adaptation of the fecundity of the human species to the exigencies of society. One of these theories, that of Mr. Doubleday, may be thought to require a passing notice, because it has of late obtained some followers, and because it derives a semblance of support from the general analogies of organic life. This theory maintains that the fecundity of the human animal, and of all other living beings, is in inverse proportion to the quantity of nutriment: that an underfed population multiplies rapidly, but that all classes in comfortable circumstances are, by a physiological law, so unprolific, as seldom to keep up their numbers without being recruited from a poorer class. There is no doubt that a positive excess of nutriment, in animals as well as in fruit trees, is unfavourable to reproduction; and it is quite possible, though by no means proved, that the physiological conditions of fecundity may exist in the greatest degree when the supply of food is somewhat stinted. But any one who might be inclined to draw from this, even if admitted, conclusions at variance with the principles of Mr. Malthus, needs only be invited to look through a volume of the Peerage, and observe the enormous families, almost universal in that class; or call to mind the large families of the English clergy, and generally of the middle classes of England. It is, besides, well remarked by Mr. Carey, that, to be consistent with Mr. Doubleday's theory, the increase of the population of the United States, apart from immigration, ought to be one of the slowest on record. Mr. Carey has a theory of his own, also grounded on a physiological truth, that the total sum of nutriment received by an organized body directs itself in largest proportion to the parts of the system which are most used; from which he anticipates a diminution in the fecundity of human beings, not through more abundant feeding, but through the greater use of their brains incident to an advanced civilization. There is considerable plausibility in this speculation, and experience may hereafter confirm it. But the change in the human constitution which it supposes, if ever realized, will conduce to the expected effect rather by rendering physical self-restraint easier, than by dispensing with its necessity; since the most rapid known rate of multiplication is quite compatible with a very sparing employment of the multiplying power. The obstacle to a just understanding