What was the sketch that he thus committed to paper in 1844, and submitted to the judgment of his friend Hooker? It was the germ of the theory of natural selection. According to that theory, organic development is due to the survival of the fittest among innumerable variations, good, bad, and indifferent, from one or more parent stocks. Darwin's reading of Malthus had suggested to him (apparently as early as the date of publication of the 'Naturalist's Journal') the idea that every species of plant and animal must always be producing a far greater number of seeds, eggs, germs, or young offspring than could possibly be needed for the maintenance of the average number of the species. Of these young, by far the greater number must always perish from generation to generation, for want of space, of food, of air, of raw material. The survivors in each brood must be those naturally best adapted for survival. The many would be eaten, starved, overrun, or crowded out; the few that survive would be those that possessed any special means of defence against aggressors, any special advantage for escaping starvation, any special protection against overrunning or overcrowding foes. Animals and plants, Darwin found on inquiry and investigation, tended to vary under diverse circumstances from the parent or parents that originally produced them. These variations were usually infinitesimal in amount, but sometimes more considerable or even striking. If any particular variation tended in any way to preserve the life of the creatures that exhibited it, beyond the average of their like competitors, that variation would in the long run survive, and the individuals that possessed it, being thus favoured in the struggle for existence, would replace the less adapted form from which they sprang. Darwinism is Malthusianism on the large scale: it is the application of the calculus of population to the wide facts of universal life.