Some Salient Points in the Science of the Earth

by Sir John William Dawson

We may here dismiss altogether that form in which these questions present themselves to the biologist, when he experiments as to the evolution of living forms from dead liquids or solids attacking the unsolved problem of spontaneous generation. Nor need we enter on the vast field of discussion as to modern animals and plants opened up by Darwin and others. I shall confine myself altogether to that historical or palæontological aspect in which life presents itself when we study the fossil remains entombed in the sediments of the earth's crust, and which will enable me at least to show why some students of fossils hesitate to give in their adhesion to any of the current notions as to the origin of species. It will also be desirable to avoid, as far as possible, the use of the term "evolution," as this has recently been employed in so many senses, whether of development or causation, as to have become nearly useless for any scientific purpose; and that when I speak of creation of species, the term is to be understood not in the arbitrary sense forced on it by some modern writers, but as indicating the continuous introduction of new forms of life under definite laws, but by a power not emanating from within themselves, nor from the inanimate nature surrounding them.[68]

[68] The terms Derivation, Development and Causation have clear and definite meanings, and it is preferable, wherever possible, to use one or other of these.

If we were to follow the guidance of those curious analogies which present themselves when we consider the growth of the individual plant or animal from the spore or the ovum, and the development of vegetable and animal life in geological time—analogies which, however, it must be borne in mind can have no scientific value whatever, inasmuch as that similarity of conditions which alone can give force to reasoning from analogy in matters of science, is wholly wanting—we should expect to find in the oldest rocks embryonic forms alone, but of course embryonic forms suited to exist and reproduce themselves independently.[69]

[69] I may be pardoned for taking an example of the confusion of thought which this mode of reasoning has introduced into Biology from a clever article in the Contemporary written by a very able and much-esteemed biologist. He says: "The morphological distance between a newly hatched frog's tadpole and the adult frog is almost as great as that between the adult lancelet and the newly hatched larvæ of the lamprey." The "morphological distance" truly, but what of the physiological distance between the young and adult of the same animal and two adult animals between which is placed the great gulf of specific and generic diversity which within human experience neither has been known to pass?

I need not say to palæontologists that this is not what we actually find in the primordial rocks. I need but to remind them of the early and remarkable development of such forms as the Trilobites, the Lingulidæ and the Pteropods, all of them highly complex and specialized types, and remote from the embryonic stages of the groups to which they severally belong. In the case of the Trilobites, one need merely consider the beautiful symmetry of their parts, both transversely and longitudinally, their division into distinct regions, the necessary complexity of their muscular and nervous systems, their highly complex visual organs, the superficial ornamentation and microscopic structure of their crusts, their advanced position among Crustaceans, indicated by their strong affinity with the Arachnidans or spiders and scorpions. (See figures prefixed.)

All these characters give them an aspect far from embryonic, while, as Barrande has pointed out, this advanced position of the group has its significance greatly strengthened by the fact that in early primordial times we have to deal not with one species, but with a vast and highly differentiated group, embracing forms of many and varied subordinate types. As we shall see, these and other early animals may be regarded as of generalized types, but not as embryonic. Here, then, meets us at the outset the fact that in as far as the great groups of annulose and molluscous animals are concerned, we can trace these back no farther than to a period in which they appear already highly advanced, much specialized and represented by many diverse forms. Either, therefore, these great groups came in on this high initial plane, or we have scarcely reached half way back in the life-history of our planet.

We have, here, however, by this one consideration, attained at once to two great and dominant laws regulating the history of life. First, the law of continuity, whereby new forms come in successively, throughout geological time, though, as we shall see, with periods of greater or less frequency. Secondly, the law of specialization of types, whereby generalized forms are succeeded by those more special, and this probably connected with the growing specialization of the inorganic world. It is this second law which causes the parallelism between the history of successive species and that of the embryo.

We have already considered the claims which Eozoon and its contemporaries may urge to recognition, as beginnings of life; but when we ascend from the Laurentian beds, we find ourselves in a barren series of conglomerates, sandstones, and other rocks, indicating shore rather than sea conditions, and remarkably destitute of indications of life. These are the Huronian beds, and possibly other series associated with them. They have afforded spicules of sponges, casts of burrows of worms, obscure forms, which may represent crustaceans or mollusks, markings of unknown origin, and some laminated forms which may perhaps represent remains of Eozoon, though their structures are imperfectly preserved. These are sufficient to show that marine life continued in some forms, and to encourage the hope that a rich pre-Cambrian fauna may yet be discovered.