The interest attached to this now extinct bird has induced some correspondents of the Zoologist to attempt an enumeration of the specimens, both of the bird and of its eggs, (which from their great size, as well as from their rarity, have always had a value with collectors,) known to be preserved in cabinets. The result is that English collections contain 14 birds and 23 eggs; those of continental Europe, 11 birds and 20 eggs; the United States, 1 bird and 2 eggs:—the total being 26 birds and 45 eggs.
It would appear that the rock off the south of Iceland which was the chief breeding resort of the Great Auk, and which from that circumstance bore the name or "Geir-fulga Sker," sank to the level of the sea during a volcanic disturbance in or about the year 1830. "Such disappearance of the fit and favourable breeding-places of the Alca impennis," observes Professor Owen, "must form an important element in its decline towards extinction." One might think that there would be rocks enough left for the birds to choose a fresh station; but really we do not know what are the elements of choice in such a case: some peculiarities exist which make one particular rock to be selected by sea-fowl, when others apparently to us as suitable are quite neglected; but we do not know what they are. Possibly when Geir-fulga Sker sank, there was no other islet fit to supply the blank. Possibly, too, the submersion took place during the breeding season, drowning the eggs or young. If this was the case, it would indeed be "a heavy blow and great discouragement" to the dwindling Alcine nation.
Mr Darwin speaks of a large wolf-like Fox (Canis antarcticus) which at the time of his voyage was common to both the Falkland Islands, but absolutely confined to them. He says, "As far as I am aware, there is no other instance in any part of the world, of so small a mass of broken land, distant from a continent, possessing so large an aboriginal quadruped peculiar to itself. Their numbers have rapidly decreased; they are already banished from that half of the island which lies to the eastward of the neck of land between St Salvador Bay and Berkeley Sound. Within a very few years after these islands shall have become regularly settled, in all probability this fox will be classed with the Dodo, as an animal which has perished from the face of the earth."[67]
The Musk Ox (Ovibos moschatus), a long-haired ruminant, resembling what you would suppose a cross between a bull and a sheep might be,—formerly an inhabitant of Britain with the Elephant and the Hyena, but now found only on the polar margins of North America,—is becoming very scarce; and it is probable that before long its last representative will leave its bones with those of the lamented Franklin and his companions.
From the more perishable character of vegetable tissues we have far less data for determining the extinction of plant species; but analogy renders it highly probable that these also have died out, and are dying in a corresponding ratio with animals. I am not aware that a single example can be adduced of a plant that has certainly ceased to exist during the historic era. But Humboldt mentions a very remarkable tree in Mexico, of which it is believed only a single specimen remains in a state of nature. It is the Hand-tree (Cheirostemon platanoides), a sterculaceous plant with large plane-like leaves, and with the anthers connected together in such a manner as to resemble a hand or claw rising from the beautiful purplish-red blossoms. "There is in all the Mexican free States only one individual remaining, one single primeval stem of this wonderful genus. It is supposed not to be indigenous, but to have been planted by a king of Toluca about five hundred years ago. I found that the spot where the Arbol de las Manitas stands is 8825 feet above the level of the sea. Why is there only one tree of the kind? Whence did the kings of Toluca obtain the young tree, or the seed? It is equally enigmatical that Montezuma should not have possessed one of these trees in his botanical gardens of Huaxtepec, Chapoltepec, and Iztapalapan, which were used as late as by Philip the Second's physician, Hernandez, and of which gardens traces still remain; and it appears no less striking that the Hand-tree should not have found a place among the drawings of subjects connected with Natural History, which Nezahual Coyotl, king of Tezcuco, caused to be made half a century before the arrival of the Spaniards."
There is an example of this interesting plant growing in one of the conservatories at Kew, but I do not know whence it was obtained. It has been asserted that it grows wild in the forests of Guatemala.
Leaving plants out of consideration from lack of adequate data, we find that a considerable number of species of animals have certainly ceased to exist since man inhabited the globe. There have been, doubtless, many others that have shared the same fate, which we know nothing about. It is only within the last hundred years that we have had anything approaching to an acquaintance with the living fauna of the earth; yet, during that time some seven or eight creatures we know have been extinguished. Fully half of these,—the Auk, the Didunculus, the Notornis, and the Nestor,—within the last ten years! It would really seem as if the more complete and comprehensive an acquaintance with the animals of the world became, the more frequently this strange phenomenon of expiring species was presented to us. Perhaps it is not extravagant to suppose that—including all the invertebrate animals, the countless hosts of insects, and all the recondite forms that dwell in the recesses of the ocean—a species fades from existence every year. All the examples that have been given were either Mammalia or Birds, (the Colossochelys only excepted:) now these, though the most conspicuous and best known, are almost the least populous classes of living beings. There is no reason whatever for concluding that the law of mortality of species does not extend to all the other classes, vertebrate and invertebrate, in an equal ratio, so that my estimate will appear, I think, a very moderate one. Yet it is a startling thought, and one which the mind does not entertain without a measure of revulsion, that the passing of every century in the world's history has left its fauna minus a hundred species of animals that were denizens of the earth when it began. I was going to say "left the fauna so much poorer;" but that I am not sure of. The term would imply that the blanks are not filled up; and that, I repeat, I am not sure of. Probability would suggest that new forms are continually created to supply the lack of deceased ones; and it may be that some, at least, of the creatures ever and anon described as new to science, especially in old and well-searched regions, may be newly called into being, as well as newly discovered. It may be so, I say; I have no evidence that it is so, except the probability of analogy; we know that the rate of mortality among individuals of a species, speaking generally, is equalled by the rate of birth, and we may suppose this balance of life to be paralleled when the unit is a species, and not an individual. If the Word of God contained anything either in statement or principle contrary to such a supposition, I would not entertain it for a moment, but I do not know that it does. I do not know that it is anywhere implied that God created no more after the six days' work was done. His Sabbath-rest having been broken by the incoming of sin, we know from John v. 17, that He continued to work without interruption; and we may fairly conclude that progressive creation was included as a part of that unceasing work.
I know not whether my readers will take the same concern as I do in this subject of the dying-out of species, but to me it possesses a very peculiar interest. Death is a mysterious event, come when and how it will; and surely the departure from existence of a species, of a type of being, that has subsisted in contemporary thousands of individuals, for thousands of years, is not less imposingly mysterious than that of the individual exemplar.
We do not know with any precision what are the immediate causes of death in a species. Is there a definite limit to life imposed at first? or is this limit left, so to speak, to be determined by accidental circumstances? Perhaps both: but if the latter, what are those circumstances?
Professor Owen says:—"There are characters in land animals rendering them more obnoxious to extirpating influences, which may explain why so many of the larger species of particular groups have become extinct, whilst smaller species of equal antiquity have survived. In proportion to its bulk is the difficulty of the contest which the animal has to maintain against the surrounding agencies that are ever tending to dissolve the vital bond, and subjugate the living matter to the ordinary chemical and physical forces. Any changes, therefore, in such external agencies as a species may have been originally adapted to exist in, will militate against that existence in a degree proportionate to the size which may characterise the species. If a dry season be gradually prolonged, the large mammal will suffer from the drought sooner than the small one; if such alteration of climate affect the quantity of vegetable food, the bulky herbivore will first feel the effects of stinted nourishment; if new enemies be introduced, the large and conspicuous animal will fall a prey while the smaller kinds conceal themselves and escape. Small quadrupeds, moreover, are more prolific than large ones. Those of the bulk of the mastodons, megatheria, glyptodons, and diprotodons, are uniparous. The actual presence, therefore, of small species of animals in countries where larger species of the same natural families formerly existed, is not the consequence of degeneration—of any gradual diminution of the size—of such species, but is the result of circumstances which may be illustrated by the fable of 'the Oak and the Reed;' the smaller and feebler animals have bent and accommodated themselves to changes to which the larger species have succumbed."[68]