Darwin, and After Darwin, Volumes 1 and 3 / An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions

by George John Romanes

In geological treatises, published not many years ago, mammals were always spoken of as having abruptly come in at the commencement of the tertiary series. And now one of the richest known accumulations of fossil mammals belongs to the middle of the secondary series; and true mammals have been discovered in the new red sandstone at nearly the commencement of this great series. Cuvier used to urge that no monkey occurred in any tertiary stratum; but now extinct species have been discovered in India, South America, and in Europe as far back as the miocene stage. Had it not been for the rare accident of the preservation of footsteps in the new red sandstone of the United States, who would have ventured to suppose that, no less than at least thirty kinds of bird-like animals, some of gigantic size, existed during that period? Not a fragment of bone has been discovered in these beds. Not long ago palæontologists maintained that the whole class of birds came suddenly into existence during the eocene period; but now we know, on the authority of Professor Owen, that a bird certainly lived during the deposition of the upper green-sand. And still more recently that strange bird, the Archeopteryx ... has been discovered in the oolitic slates of Solenhofen. Hardly any recent discovery shows more forcibly than this, how little we as yet know of the former inhabitants of the world.

I may give another instance, which, from having passed under my own eyes, has much struck me. In a memoir on Fossil Sessile Cirripedes, I stated that, from the number of existing and extinct tertiary species; from the extraordinary abundance of the individuals of many species all over the world from the Arctic regions to the equator, inhabiting various zones of depths from the upper tidal limits to 50 fathoms; from the perfect manner in which specimens are preserved in the oldest tertiary beds; from the ease with which even a fragment of a valve can be recognized; from all these circumstances, I inferred that had sessile cirripedes existed during the secondary periods, they would certainly have been preserved and discovered; and as not one species had then been discovered in beds of this age, I concluded that this great group had been suddenly developed at the commencement of the tertiary series. This was a sore trouble to me, adding as I thought one more instance of the abrupt appearance of a great group of species. But my work had hardly been published, when a skilful palæontologist, M. Bosquet, sent me a drawing of a perfect specimen of an unmistakeable sessile cirripede, which he had himself extracted from the chalk of Belgium. And, as if to make the case as striking as possible, this sessile cirripede was a Chthamalus, a very common, large, and ubiquitous genus, of which not one specimen has as yet been found even in any tertiary stratum. Still more recently, a Pyrgoma, a member of a distinct sub-family of sessile cirripedes, has been discovered by Mr. Woodward in the upper chalk; so that we now have abundant evidence of the existence of this group of animals during the secondary period.

The case most frequently insisted on by palæontologists of the apparently sudden appearance of a whole group of species, is that of the teleostean fishes, low down, according to Agassiz, in the Chalk period. This group includes the large majority of existing species. But certain Jurassic and Triassic forms are now commonly admitted to be teleostean; and even some palæozoic forms have been thus classed by one high authority. If the teleosteans had really appeared suddenly in the northern hemisphere, the fact would have been highly remarkable; but it would not have formed an insuperable difficulty, unless it could likewise have been shown that at the same period the species were suddenly and simultaneously developed in other quarters of the world. It is almost superfluous to remark that hardly any fossil fish are known from south of the equator; and by running through Pictet’s Palæontology it will be seen that very few species are known from several formations in Europe. Some few families of fish now have a confined range; the teleostean fish might formerly have had a similarly confined range, and after having been largely developed in some one sea, might have spread widely. Nor have we any right to suppose that the seas of the world have always been so freely open from south to north as they are at present. Even at this day, if the Malay Archipelago were converted into land, the tropical parts of the Indian Ocean would form a large and perfectly enclosed basin, in which any great group of marine animals might be multiplied; and here they would remain confined, until some of the species became adapted to a cooler climate, and were enabled to double the southern capes of Africa or Australia, and thus reach other and distant seas.

From these considerations, from our ignorance of the geology of other countries beyond the confines of Europe and the United States; and from the revolution in our palæontological knowledge effected by the discoveries of the last dozen years, it seems to me to be about as rash to dogmatize on the succession of organic forms throughout the world, as it would be for a naturalist to land for five minutes on some one barren point in Australia, and then to discuss the number and range of its productions[53].

In view of all the foregoing facts and considerations, it appears to me that the second difficulty on our list is completely answered. Indeed, even on a moderate estimate of the imperfection of the geological record, the wonder would have been if many cases had not occurred where groups of species present the fictitious appearance of having been suddenly and simultaneously created in the particular formations where their remains now happen to be observable.

Turning next to the third objection, there cannot be any question that every here and there in the geological series animals occur of a much higher grade zoologically than the theory of evolution would have expected to find in the strata where they are found. At any rate, speaking for myself, I should not have antecedently expected to meet with such highly differentiated insects as butterflies and dragonflies in the middle of the Secondaries: still less should I have expected to encounter beetles, cockroaches, spiders, and May-flies in the upper and middle Primaries—not to mention an insect and a scorpion even in the lower. And I think the same remark applies to a whole sub-kingdom in the case of Vertebrata. For although it is only the lowest class of the sub-kingdom which, so far as we positively know, was represented in the Devonian and Silurian formations, we must remember, on the one hand, that even a cartilaginous or ganoid fish belongs to the highest sub-kingdom of the animal series; and, on the other hand, that such animals are thus proved to have abounded in the very lowest strata where there is good evidence of there having been any forms of life at all. Lastly, the fact that Marsupials occur in the Trias, coupled with the fact that the still existing Monotremata are what may be termed animated fossils, referring us by their lowly type of organization to some period enormously more remote,—these facts render it practically certain that some members of this very highest class of the highest sub-kingdom must have existed far back in the Primaries.

These things, I say, I should not have expected to find, and I think all other evolutionists ought to be prepared to make the same acknowledgment. But as these things have been found, the only possible way of accounting for them on evolutionary principles is by supposing that the geological record is even more imperfect than we needed to suppose in order to meet the previous objections. I cannot see, however, why evolutionists should be afraid to make this acknowledgment. For I do not know any reason which would lead us to suppose that there is any common measure between the distances marked on our tables of geological formations, and the times which those distances severally represent. Let the reader turn to the table on page [163], and then let him say why the 30,000 feet of so-called Azoic rocks may not represent a greater duration of time than does the thickness of all the Primary rocks above them put together. For my own part I believe that this is probably the case, looking to the enormous ages during which these very early formations must have been exposed to destructive agencies of all kinds, now at one time and now at another, in different parts of the world. And, of course, we are without any means of surmising what ranges of time are represented by the so-called Primeval rocks, for the simple reason that they are non-sedimentary, and non-sedimentary rocks cannot be expected to contain fossils.

But, it will be answered, the 30,000 feet of Azoic rocks, lying above the Primeval, are sedimentary to some extent: they are not all completely metamorphic: yet they are all destitute of fossils. This is the fourth and last difficulty which has to be met, and it can only be met by the considerations which have been advanced by Lyell and Darwin. The former says:—

The total absence of any trace of fossils has inclined many geologists to attribute the origin of the most ancient strata to an azoic period, or one antecedent to the existence of organic beings. Admitting, they say, the obliteration, in some cases, of fossils by plutonic action, we might still expect that traces of them would oftener be found in certain ancient systems of slate, which can scarcely be said to have assumed a crystalline structure. But in urging this argument it seems to be forgotten that there are stratified formations of enormous thickness, and of various ages, some of them even of tertiary date, and which we know were formed after the earth had become the abode of living creatures, which are, nevertheless, in some districts, entirely destitute of all vestiges of organic bodies[54].

He then proceeds to mention sundry causes (in addition to plutonic action) which are adequate to destroy the fossiliferous contents of stratified rocks, and to show that these may well have produced enormous destruction of organic remains in these oldest of known formations.