It is of great interest to learn that Wallace as well as Darwin was directed to natural selection by Malthus’ Essay. Hence, as the late Professor Milnes Marshall has pointed out (Lectures on the Darwinian Theory, pp. 212, 213), the laws of the multiplication and extinction of man suggested to both naturalists those more general laws by which it was possible to understand the development of the whole animal and vegetable worlds. There is a tremendous contrast between these two discoverers, in the speed with which they respectively developed their ideas on the subject into a shape which satisfied them as suitable for publication. Wallace, after the inspiration which followed his reflections upon Malthus, had “thought out almost the whole of the theory” in two hours, and in three evenings had completed his essay. Darwin, receiving the same inspiration from the same source, in October 1838, wrote a brief account of it after four years’ reflection and work, and finished a longer account two years later, but was not prepared to give anything to the public until he was compelled to do so fourteen years later in 1858. All this delay was of the greatest advantage when a full exposition of the theory finally came before the world in the “Origin of Species”; for all difficulties had been fully considered and answered beforehand, while the wealth of new facts by which it was supported compelled a respectful hearing for the theory itself. [Sidenote: WALLACE’S VIEWS.] Wallace, like Darwin, was convinced of evolution before he discovered any principle which supplied a motive cause for the process. This conviction is expressed very clearly in his interesting essay already alluded to “On the Law which has regulated the Introduction of New Species” (Ann. and Mag., Nat. Hist., 1855, p. 184; reprinted without alteration in his Essays on Natural Selection). The law he states in these words:-- “Every species has come into existence coincident both in time and space with a pre-existing closely allied species,” a law which, as he justly claims for it,