When we consider how soon some plants which spread rapidly, by seeds or roots, would cover an area equal to the surface of the globe,…how soon some fishes would fill the ocean if all their ova became full-grown fishes, we are tempted to say that every organism, whether animal or vegetable, is contending for the possession of the planet.…Nature opposes to this many obstacles, as climate, myriads of brute and also human foes, and of competitors which may preoccupy the ground. Each suggests an immense and wonderfull greediness and tenacity of life…as if bent on taking entire possession of the globe wherever the climate and soil will permit. And each prevails as much as it does, because of the ample preparations it has made for the contest,—it has secured a myriad chances,—because it never depends on spontaneous generation to save it.

Journal , March 22, 1861