2. It is natural to all animals to propagate their kind, natural therefore also to man; and being natural, it is so far forth also a good thing, unless we are to say with the Manicheans, that the whole of corporeal nature is an evil creation. Nay, so urgent is the natural appetite here, that we must argue the existence, not of a mere permission, but of an exigency of nature, and consequent command of God (_Ethics_, c. vi., s. ii., nn. 11, 12, p. 122), for the propagation of the human species. Besides, there is in the individual the duty of self-preservation, therefore likewise in the race. Again, the old cannot subsist at all without the support of the young, nor lead a cheerful existence without their company. Imagine a world with no youth in it, a winter without a spring! 3. There is this difference between self-preservation and the preservation of the race, that if a man will not eat, none can eat for him; but if one man omit the propagation of his kind, another can take it up. There are many things necessary for the good of mankind, which are not to be done by every individual. Not all are to be soldiers, nor all builders, though houses are needful, and sometimes war. Nor is it desirable that the human race should be multiplied to its utmost capacity. It is enough here to mention without discussing the teaching of Malthus, how population presses on the means of subsistence, the latter increasing in an arithmetical, the former in a geometrical ratio. Without going the whole way with Malthus, modern economical writers are commonly a little Malthusian, and shrink from giving to all and each of their species the word to "increase and multiply."