Conchologists, he says, did not care to collect or study fossil shells, because they had lost their lustre, colors, and beauty, and they were rejected from collections on this account as “dead” and uninteresting. “But,” he adds, “since attention has been drawn to the fact that these fossils are extremely valuable monuments for the study of the revolutions which have taken place in different regions of the earth, and of the changes which the beings living there have themselves successively undergone (in my lectures I have always insisted on these considerations), consequently the search for and study of fossils have excited special interest, and are now the objects of the greatest interest to naturalists.”
Lamarck then combats the views of several naturalists, undoubtedly referring to Cuvier, that the fossils are extinct species, and that the earth has passed through a general catastrophe (un bouleversement universel) with the result that a multitude of species of animals and plants were consequently absolutely lost or destroyed, and remarks in the following telling and somewhat derisive language:
“A universal catastrophe (bouleversement) which necessarily regulates nothing, mixes up and disperses everything, is a very convenient way to solve the problem for those naturalists who wish to explain everything, and who do not take the trouble to observe and investigate the course followed by nature as respects its production and everything which constitutes its domain. I have already elsewhere said what should be thought of this so-called universal overturning of the globe; I return to fossils.
“It is very true that, of the great quantity of fossil shells gathered in the different countries of the earth, there are yet but a very small number of species whose living or marine analogues are known. Nevertheless, although this number may be very small, which no one will deny, it is enough to suppress the universality announced in the proposition cited above.
“It is well to remark that among the fossil shells whose marine or living analogues are not known, there are many which have a form closely allied to shells of the same genera known to be now living in the sea. However, they differ more or less, and cannot be rigorously regarded as the same species as those known to be living, since they do not perfectly resemble them. These are, it is said, extinct species.
“I am convinced that it is possible never to find, among fresh or marine shells, any shells perfectly similar to the fossil shells of which I have just spoken. I believe I know the reason; I proceed to succinctly indicate, and I hope that it will then be seen, that although many fossil shells are different from all the marine shells known, this does not prove that the species of these shells are extinct, but only that these species have changed as the result of time, and that actually they have different forms from those individuals whose fossil remains we have found.”
Then he goes on in the same strain as in the opening discourse, saying that nothing terrestrial remains constant, that geological changes are continually occurring, and that these changes produce in living organisms a diversity of habits, a different mode of life, and as the result modifications or developments in their organs and in the shape of their parts.
“We should still realize that all the modifications which the organism undergoes in its structure and form as the result of the influence of circumstances which would influence this being, are propagated by generation, and that after a long series of ages not only will it be able to form new species, new genera, and even new orders, but also each species will even necessarily vary in its organization and in its forms.
“We should not be more surprised then if, among the numerous fossils which occur in all the dry parts of the globe and which offer us the remains of so many animals which have formerly existed, there should be found so few of which we know the living analogues. If there is in this, on the contrary, anything which should astonish us, it is to find that among these numerous fossil remains of beings which have lived there should be known to us some whose analogues still exist, from a germ to a vast multitude of living forms, of different and ascending grades of perfection, ending in man.
“This fact, as our collection of fossils proves, should lead us to suppose that the fossil remains of the animals whose living analogues we know are the less ancient fossils. The species to which each of them belongs had doubtless not yet time to vary in any of its forms.
“We should, then, never expect to find among the living species the totality of those that we meet with in the fossil state, and yet we cannot conclude that any species can really be lost or extinct. It is undoubtedly possible that among the largest animals some species have been destroyed as a result of the multiplication of man in the regions where they live. But this conjecture cannot be based on the consideration of fossils alone; we can only form an opinion in this respect when all the inhabited parts of the globe will have become perfectly known.”
Lamarck did not have, as we now have, a knowledge of the geological succession of organic forms. The comparatively full and detailed view which we possess of the different vast assemblages of plant and animal life which have successively peopled the surface of our earth is a vision on which his eyes never rested. His slight, piecemeal glimpse of the animal life of the Paris Basin, and of the few other extinct forms then known, was all he had to depend upon or reason from. He was not disposed to believe that the thread of life once begun in the earliest times could be arbitrarily broken by catastrophic means; that there was no relation whatever between the earlier and later faunas. He utterly opposed Cuvier’s view that species once formed could ever be lost or become extinct without ancestors or descendants. He on the contrary believed that species underwent a slow modification, and that the fossil forms are the ancestors of the animals now living. Moreover, Lamarck was the inventor of the first genealogical tree; his phylogeny, in the second volume of his Philosophie zoologique (p. 463), proves that he realized that the forms leading up to the existing ones were practically extinct, as we now use the word. Lamarck in theory was throughout, as Houssay well says, at one with us who are now living, but a century behind us in knowledge of the facts needed to support his theory.
In this first published expression of his views on palæontology, we find the following truths enumerated on which the science is based: (1) The great length of geological time; (2) The continuous existence of animal life all through the different geological periods without sudden total extinctions and as sudden recreations of new assemblages; (3) The physical environment remaining practically the same throughout in general, but with (4) continual gradual but not catastrophic changes in the relative distribution of land and sea and other modifications in the physical geography, changes which (5) caused corresponding changes in the habitat, and (6) consequently in the habits of the living beings; so that there has been all through geological history a slow modification of life-forms.
Thus Lamarck’s idea of creation is evolutional rather than uniformitarian. There was, from his point of view, not simply a uniform march along a dead level, but a progression, a change from the lower or generalized to the higher or specialized—an evolution or unfolding of organic life. In his effort to disprove catastrophism he failed to clearly see that species, as we style them, became extinct, though really the changes in the species practically amounted to extinctions of the earlier species as such. The little that was known to Lamarck at the time he wrote, prevented his knowing that species became extinct, as we say, or recognizing the fact that while some species, genera, and even orders may rise, culminate, and die, others are modified, while a few persist from one period to another. He did, however, see clearly that, taking plant and animal life as a whole, it underwent a slow modification, the later forms being the descendants of the earlier; and this truth is the central one of modern palæontology.
Lamarck’s first memoir on fossil shells, in which he described many new species, was published in 1802, after the appearance of his Hydrogéologie, to which he refers. It was the first of a series of descriptive papers, which appeared at intervals from 1802 to 1806. He does not fail to open the series of memoirs with some general remarks, which prove his broad, philosophic spirit, that characterizing the founder of a new science. He begins by saying that the fossil forms have their analogues in the tropical seas. He claims that there was evident proof that these molluscs could not have lived in a climate like that of places in which they now occur, instancing Nautilius pompilius, which now lives in the seas of warm countries; also the presence of exotic ferns, palms, fossil amber, fossil gum elastic, besides the occurrence of fossil crocodiles and elephants both in France and Germany.[83]
Hence there have been changes of climate since these forms flourished, and, he adds, the intervals between these changes of climate were stationary periods, whose duration was practically without limit. He assigns a duration to these stationary or intermediate periods of from three to five million years each—“a duration infinitely small relative to those required for all the changes of the earth’s surface.”