horned cattle (so different in shape of body) have been derived from the same parent stock1? Yet this transition has been effected in the same country, and in a far shorter time, than would be probable in a wild state, both contingencies highly favourable for the future hypothetical geologists being enabled

to trace the variation.

1 Origin, Ed. i. p. 299, vi. p. 437.

CHAPTER V

GRADUAL APPEARANCE AND DISAPPEARANCE

OF SPECIES1

In the Tertiary system, in the last uplifted beds, we find all the species recent and living in the immediate vicinity; in rather older beds we find only recent species, but some not living in the immediate vicinity 2; we then find beds with two or three or a few more extinct or very rare species; then considerably more extinct species, but with gaps in the regular increase; and finally we have beds with only two or three or not one living species. Most geologists believe that the gaps in the percentage, that is the sudden increments, in the number of the extinct species in the stages of the Tertiary system are due to the imperfection of the geological record. Hence we are led to believe that the species in the Tertiary system have been gradually introduced; and from analogy to carry on the same view to the Secondary formations. In these latter, however, entire groups of species generally come in abruptly; but this would naturally result, if, as argued in the foregoing chapter, these Secondary deposits are separated by wide epochs. Moreover it is important to observe that, with our increase of knowledge, the gaps between the older formations become fewer and smaller; geologists of

1 This chapter corresponds to ch. X of Origin, Ed. i., vi. ch. XI, “On the geological succession of organic beings."

2 Origin, Ed. i. p. 312, vi. p. 453.

a few years standing remember how beautifully has the Devonian system1 come in between the Carboniferous and Silurian formations. I need hardly observe that the slow and gradual appearance of new forms follows from our theory, for to form a new species, an old one must not only be plastic in its organization, becoming so probably from changes in the conditions of its existence, but a place in the natural economy of the district must [be made,] come to exist, for the selection of some new modification of its structure, better fitted to the surrounding conditions than are the other individuals of the same or other species 2.

In the Tertiary system the same facts, which make us admit as probable that new species have slowly appeared, lead to the admission that old ones have slowly disappeared, not several together, but one after another; and by analogy one is induced to extend this belief to the Secondary and Palæozoic epochs. In some cases, as the subsidence of a flat country, or the breaking or the joining of an isthmus, and the sudden inroad of many new and destructive species, extinction might be locally sudden. The view entertained by many geologists, that each fauna of each Secondary epoch has been suddenly destroyed over the whole world, so that no succession could be left for the production of new forms, is subversive of my theory, but I see no grounds whatever to admit such a view. On the

1 In the margin the author has written "Lonsdale." This refers to W. Lonsdale's paper "Notes on the age of the Limestone of South Devonshire," Geolog. Soc. Trans., Series 2, vol. v. 1840, p. 721. According to Mr H. B. Woodward (History of the Geological Society of London, 1907, p. 107) "Lonsdale's 'important and original suggestion of the existence of an intermediary type of Palæozoic fossils, since called Devonian,' led to a change which was then 'the greatest ever made at one time in the classification of our English formations'." Mr Woodward's quotations are from Murchison and Buckland.

(Note in original.) Better begin with this. If species really, after catastrophes, created in showers over world, my theory false. (In the above passage the author is obviously close to his theory of divergence.)

contrary, the law, which has been made out, with reference to distinct epochs, by independent observers, namely, that the wider the geographical range of a species the longer is its duration in time, seems entirely opposed to any universal extermination1. The fact of species of mammiferous animals and fish being renewed at a quicker rate than mollusca, though both aquatic; and of these the terrestrial genera being renewed quicker than the marine; and the marine mollusca being again renewed quicker than the Infusorial animalcula, all seem to show that the extinction and renewal of species does not depend on general catastrophes, but on the particular relations of the several classes to the conditions to which they are exposed 2.

Some authors seem to consider the fact of a few species having survived3 amidst a number of extinct forms (as is the case with a tortoise and a crocodile out of the vast number of extinct sub-Himalayan fossils) as strongly opposed to the view of species being mutable. No doubt this would be the case, if it were presupposed with Lamarck that there was some inherent tendency to change and development in all species, for which supposition I see no evidence. As we see some species at present adapted to a wide range of conditions, so we may suppose that such species would survive unchanged and unexterminated for a long time; time generally being from geological causes a correlative of changing conditions. How at present one species becomes adapted to a wide range, and another species to a restricted range of conditions, is of difficult explanation.

1 Opposite to this passage the author has written "d'Archiac, Forbes, Lyell."

2 This passage, for which the author gives as authorities the names of Lyell, Forbes and Ehrenberg, corresponds in part to the discussion beginning on p. 313 of Origin, Ed. i., vi. p. 454.

3 The author gives Falconer as his authority: see Origin, Ed. i. p. 313, vi. p. 454.

Extinction of species.

The extinction of the larger quadrupeds, of which we imagine we better know the conditions of existence, has been thought little less wonderful than the appearance of new species; and has, I think, chiefly led to the belief of universal catastrophes. When considering the wonderful disappearance within a late period, whilst recent shells were living, of the numerous great and small mammifers of S. America, one is strongly induced to join with the catastrophists. I believe, however, that very erroneous views are held on this subject. As far as is historically known, the disappearance of species from any one country has been slow-the species becoming rarer and rarer, locally extinct, and finally lost1. It may be objected that this has been effected by man's direct agency, or by his indirect agency in altering the state of the country; in this latter case, however, it would be difficult to draw any just distinction between his agency and natural agencies. But we now know in the later Tertiary deposits, that shells become rarer and rarer in the successive beds, and finally disappear: it has happened, also, that shells common in a fossil state, and thought to have been extinct, have been found to be still living species, but very rare ones 2. If the rule is that organisms become extinct by becoming rarer and rarer, we ought not to view their extinction, even in the case of the larger quadrupeds, as anything wonderful and out of the common course of events. For no naturalist thinks it wonderful that one species of a genus should be rare and another abundant, notwithstanding he be

1 This corresponds approximately to Origin, Ed. i. p. 317, vi. p. 458. The case of Trigonia, a great Secondary genus of shells surviving in a single species in the Australian seas, is given as an example in the Origin, Ed. i. p. 321, vi. p. 463.