“So were it not for the immense consumption as food which is made in nature of animals which compose the lower orders of the animal kingdom, these animals would soon overpower and perhaps destroy, by their enormous numbers, the more highly organized and perfect animals which compose the first classes and the first orders of this kingdom, so great is the difference in the means and facility of multiplying between the two.
“But nature has anticipated the dangerous effects of this vast power of reproduction and multiplication. She has prevented it on the one hand by considerably limiting the duration of life of these beings so simply organized which compose the lower classes, and especially the lowest orders of the animal kingdom. On the other hand, both by making these animals the prey of each other, thus incessantly reducing their numbers, and also by determining through the diversity of climates the localities where they could exist, and by the variety of seasons—i.e., by the influences of different atmospheric conditions—the time during which they could maintain their existence.
“By means of these wise precautions of nature everything is well balanced and in order. Individuals multiply, propagate, and die in different ways. No species predominates up to the point of effecting the extinction of another, except, perhaps, in the highest classes, where the multiplication of the individuals is slow and difficult; and as the result of this state of things we conceive that in general species are preserved” (p. 22).
Here we have in anticipation the doctrine of Malthus, which, as will be remembered, so much impressed Charles Darwin, and led him in part to work out his principle of natural selection.
The author then taking up other subjects, first asserts that among the changes that animals and plants unceasingly bring about by their production and débris, it is not the largest and most perfect animals which have caused the most considerable changes, but rather the coral polyps, etc.[165] He then, after dilating on the value of the study of the invertebrate animals, proceeds to define them, and closes his lecture by describing the seven classes into which he divides this group.
II. Recherches sur l’Organisation des Corps vivans, 1802 (Opening Discourse).
The following is an abstract with translations of the most important passages relating to evolution:
That the portion of the animal kingdom treated in these lectures comprises more species than all the other groups taken together is, however, the least of those considerations which should interest my hearers.
“It is the group containing the most curious forms, the richest in marvels of every kind, the most astonishing, especially from the singular facts of organization that they present, though it is that hitherto the least considered under these grand points of view.
“How much better than learning the names and characters of all the species is it to learn of the origin, relation, and mode of existence of all the natural productions with which we are surrounded.
“First Part: Progress in structure of living beings in proportion as circumstances favor them.
“When we give continued attention to the examination of the organization of different living beings, to that of different systems which this organization presents in each organic kingdom, finally to certain changes which are seen to be undergone in certain circumstances, we are convinced:
“1. That the nature of organic movement is not only to develop the organization but also to multiply the organs and to fulfil the functions, and that at the outset this organic movement continually tends to restrict to functions special to certain parts the functions which were at first general—i.e., common to all parts of the body;
“2. That the result of nutrition is not only to supply to the developing organization what the organic movement tends to form, but besides, also by a forced inequality between the matters which are assimilated and those which are dissipated by losses, this function at a certain term of the duration of life causes a progressive deterioration of the organs, so that as a necessary consequence it inevitably causes death;
“3. That the property of the movement of the fluids in the parts which contain them is to break out passages, places of deposit, and outlets; to there create canals and consequently different organs; to cause these canals, as well as the organs, to vary on account of the diversity both of the movements and of the nature of the fluids which give rise to them; finally to enlarge, elongate, to gradually divide and solidify [the walls of] these canals and these organs by the matters which form and incessantly separate the fluids which are there in movement, and one part of which is assimilated and added to the organs, while the other is rejected and cast out;
“4. That the state of organization in each organism has been gradually acquired by the progress of the influences of the movement of fluids, and by those changes that these fluids have there continually undergone in their nature and their condition through the habitual succession of their losses and of their renewals;
“5. That each organization and each form acquired by this course of things and by the circumstances which there have concurred, were preserved and transmitted successively by generation [heredity] until new modifications of these organizations and of these forms have been acquired by the same means and by new circumstances;
“6. Finally, that from the uninterrupted concurrence of these causes or from these laws of nature, together with much time and with an almost inconceivable diversity of influential circumstances, organic beings of all the orders have been successively formed.
“Considerations so extraordinary, relatively to the ideas that the vulgar have generally formed on the nature and origin of living bodies, will be naturally regarded by you as stretches of the imagination unless I hasten to lay before you some observations and facts which supply the most complete evidence.
“From the point of view of knowledge based on observation the philosophic naturalist feels convinced that it is in that which is called the lowest classes of the two organic kingdoms—i.e., in those which comprise the most simply organized beings—that we can collect facts the most luminous and observations the most decisive on the production and the reproduction of the living beings in question; on the causes of the formation of the organs of these wonderful beings; and on those of their developments, of their diversity and their multiplicity, which increase with the concourse of generations, of times, and of influential circumstances.
“Hence we may be assured that it is only among the singular beings of these lowest classes, and especially in the lowest orders of these classes, that it is possible to find on both sides the primitive germs of life, and consequently the germs of the most important faculties of animality and vegetality.”
Modification of the organization from one end to the other of the animal chain.
“One is forced,” he says, “to recognize that the totality of existing animals constitute a series of groups forming a true chain, and that there exists from one end to the other of this chain a gradual modification in the structure of the animals composing it, as also a proportionate diminution in the number of faculties of these animals from the highest to the lowest (the first germs), these being without doubt the form with which nature began, with the aid of much time and favorable circumstances, to form all the others.”
He then begins with the mammals and descends to molluscs, annelids, and insects, down to the polyps, “as it is better to proceed from the known to the unknown;” but farther on (p. 38) he finally remarks: