The body of the book consists of historical details, and particular examples showing the checks to population in uncivilized and in civilized places, in present and in past times. The writer means to bring his conclusions home to his readers by the “longer way” of induction. As this, however, was not the way in which he himself reached them, or even stated them at first, he will ask us first of all to look at the terms of the dilemma in the light of his two original postulates[113]—(_a_) food is necessary, (_b_) the desire of marriage is permanent. What is the quickest possible increase of numbers in obedience to the second, and of food in obedience to the first? In the most crucial of the known instances, the actual rapidity of the increase of population seems to be in direct proportion to the easy possession of food; and we can infer that the ideally rapid increase would take place where all obstacles (whether material or moral) to the getting of food and rearing of a family were removed, so that nature never needed to remonstrate with instinct. “In no state that we have yet known has the power of population been left to exert itself with perfect freedom.”[114] We can guess what it would be from the animal and vegetable world, where reason does not as a matter of fact interfere with instinct in any circumstances, so far as we can judge. Benjamin Franklin, in a passage quoted by Malthus in this connection,[115] supposes that if the earth were bared of other plants it might be replenished in a few years with fennel alone. Even as things are now, fennel would fill the whole earth if the other plants would only allow it; and the same is true of each of the others. Townsend’s goats and greyhounds on Juan Fernandez are a better instance, because not hypothetical.[116] Juan Fernando, the first discoverer, had covered the island with goats from one pair.[117] The Spaniards resolved to clear it of goats, in order to make it useless to the English for provisioning. They put on shore a couple of greyhounds, whose offspring soon caused the goats to disappear. But without some few goats to eat all the dogs must have died; and the few were saved to them by their inaccessible refuges in the rocks, from which they descended at risk of their lives. In this way only the strongest and fleetest dogs and the hardiest and fleetest goats survived; and a balance was kept up between goat food and hound population. Townsend thereupon remarks that human populations are kept down by want of food precisely in the same way.