To better make sense of a book* I've been reading, today I searched for Stephen A. Forbes’s classic paper from 1887, The Lake as a Microcosm. Luckily, a copy was available at the Early Classics in Biogeography, Distribution, and Diversity Studies: To 1950 archive.
Forbes’s insight of the intricate evolutionary interdependencies of the species in lakes was impressive; his clear explanation of the complexity, within just one short paragraph, was even more so.
If one wishes to become acquainted with the black bass, for example, he will learn but little if he limits himself to that species. He must evidently study also the species upon which it depends for its existence, and the various conditions upon which these depend. He must likewise study the species with which it comes in competition, and the entire system of conditions affecting their prosperity, and by the time he has studied all these sufficiently he will find that he has run through the whole complicated mechanism of the aquatic life of the locality, both animal and vegetable, of which his species forms but a single element.A hundred years before Geerat Vermeij came out with Evolution & Escalation (Princeton University Press, 1987), Forbes had already hit upon the idea of a perennial evolutionary arms race between predators and their prey.
Every animal within these bounds has its enemies, and Nature seems to have taxed her skill and ingenuity to the utmost to furnish these enemies with contrivances for the destruction of their prey in myriads. For every defensive device with which she has armed an animal, she has invented a still more effective apparatus of destruction, and bestowed it upon some foe, thus striving with unending pertinacity, to outwit herself, and yet life does not perish in the lake, nor even oscillate to any considerable degree; but on the contrary the little community secluded here is as prosperous as if its state were one of profound and perpetual peace.
Is there a battle of evolution beneath the calm surface of this microcosm?
And what is the simple explanation behind all of this? Natural selection, of course.
We thus see that there is really a close community of interest between these two seemingly deadly foes. And next we note that this common interest is promoted by the process of natural selection; for it is the great office of this process to eliminate the unfit.What Forbes referred to as the elimination of the unfit is now known as stabilizing selection, which operates by making it more likely for the individuals with extreme traits to perish before reproducing.
*William H. Drury, Chance and Change, 1998. Review is forthcoming.