The Origin of Species . . . Chapter 11: On the Geological Succession of Organic Beings –
-- Summary by Susan Fleck

(1) New species have appeared very slowly, one after another, both on land and in waters.

• Lyell has shown that it is hardly possible to resist the evidence in the case of the several tertiary stages and every year tends to fill up the blanks between the stages. [tertiary = period of Cenozoic Era, a period with five separate epochs, ‘stages’ as Darwin calls them]

• Since the formations rich in fossils have been accumulated at wide and irregularly intermittent intervals of time [only deposited during periods of subsiding], then each ‘layer’ does not mark a new and complete act of creation, but only an occasional scene taken in an ever slowly changing drama

(2) Species belonging to different genera and classes have not changed at the same rate, or in the same degree. E.g., In the older tertiary beds a few living shells may still be found in the midst of a multitude of extinct forms. E.g., a living crocodile is found with extinct mammals and reptiles.

(3) The productions of the land seem to have changed at a quicker rate than those of the sea; . . . facts lead to the view that organisms high in the scale change more quickly than those that are low; though there are exceptions to this rule. If we compare any but the most closely related formation, all the species will be found to have undergone some change.

(4) When a species has once become extinct, we have no reason to believe that the same identical form ever reappears. Sometimes temporary migration from and then back to a specific location may make it appear this is not so.

• Any two forms—the old one and the new one—could not be identically the same; for both would almost certainly inherit different characters from their distinct progenitors. E.g., if the Rock Pigeon were to become extinct, it is incredible that a fantail (or others) could be raised from any other species of pigeon or from any other well-established race of the domestic pigeon

(5) The variability of each species is independent of that of all others; whether such variations or individual differences as may arise will be accumulated through natural selection in a greater or less degree, thus causing a greater or less amount of permanent modification, will depend on many complex contingencies

(6) Groups of species—genera and families—follow the same general rules in their appearance and disappearance as do single species, changing more or less quickly, and in a greater or lesser degree.

• A group, when it has once disappeared, never reappears—that is, its existence, as long as it lasts, is continuous. [Paleontologists who had disagreed with Darwin’s theory, admit this is true.]

• The general pattern in the fossil record is that of a gradual increase in number, until the group reaches its maximum, and then, sooner or later, a gradual decrease. The gradual increase in number of the species of a group is strictly conformable with the theory.

(7) With natural selection theory, the extinction of old forms and the production of new and improved forms are intimately connected together. The old notion of all the inhabitants of the earth having been swept away by catastrophes at successive periods is generally given up by geologists

• No fixed law determines the length of time during which any single species or any single genus endures. If we ask ourselves why this or that species is rare, we answer that something is unfavorable in its conditions of life; but what that one or several contingencies are that contributed to its extinction, if found in fossil record, we can hardly ever tell.

• The theory of natural selection is grounded on the belief that each new variety and ultimately each new species, is produced and maintained by having some advantage over those with which it comes into competition; the consequent extinction of less-favored forms almost invariably follows.

(8) We should find in two distinct regions when two formations have been deposited during nearly, but not exactly, the same general time epoch, the same general succession in the forms of life; but the species would not exactly correspond—one reason being that there will have been a little more time in one region than in the other for modification, extinction, and immigration.

• Geologists has thus reported such parallelism, with species themselves differing even when the two areas were fairly close to each other, which could also be caused if an isthmus had once separated two seas between these two areas. This also explains why a formation in one area corresponds with a blank interval in another; that is one region is subsiding during that geological time frame, and the other is lifting or remains level.

The Origin of Species . . . Chapter 11: On the Geological Succession of Organic Beings – outline – Page 2

(9) On the Affinities of Extinct Species to Each Other, and to Living Forms:

• All extinct and living species fall into a few grand classes; and this fact is at once explained on the principle of descent. As a general rule, the more ancient any form is, the more it differs from living forms. But, extinct species can all be classed either in still existing groups, or between them.

• That the extinct forms of life help to fill up the intervals between existing genera, families, and orders, is true; but this statement has often been ignored or even denied. If we confine attention either to the living or to the extinct species of the same class, the series is far less perfect than if we combine both into one system.

• Two of the examples Darwin provides: no one can deny that the Hipparion is intermediate between the existing horse and certain older ungulate forms. Even the wide interval between birds and reptiles has been shown by naturalists to be bridged over in the most unexpected manner—e.g., by the extinct Archeopteryx [a dinosaur]

• Some writers have objected to any extinct species, or group of species, being considered as intermediate between any two living species, or groups. If they mean to imply that an extinct form is directly intermediate in all its characters . . . the objection is probably valid. But in a natural classification many fossil species certainly stand between living species, and some extinct genera between living genera, even between genera belonging to distinct families. . . . the ancient members are separated by a somewhat lesser number of characters, so that the two groups formerly made a somewhat nearer approach to each other than they do now. . . .

• (10) On the State of Development of Ancient Compared with Living Forms

• After re-iterating that advance in organization is not a necessary contingent of the theory – i.e., Natural Selection may leave many creatures with simple and unimproved structures fitted for simple conditions of life—Darwin states:

• In a more general manner, new species become superior to their predecessors; for they have to beat in the struggle for life all the older forms with which they come into close competition;

• We may conclude that if under nearly similar climate the Eocene [second epoch of the Tertiary Period] inhabitants of the world could be put into competition with the [now] existing inhabitants, the former would be beaten and exterminated by the latter, and so on in the march of time.

• So that by this fundamental test of victory in the battle for life, as well as by the standard of the specialization of organs, modern forms ought to stand higher than ancient forms.

• A large majority of paleontologists would answer in the affirmative [to this conclusion].

• (11) On the Succession of the Same Types within the Same Areas, during the Later Tertiary Periods

• The fossil mammals of the Australian caves were closely allied to the living marsupials on that continent. In S. America, a relationship in the gigantic pieces of armor, like those of the armadillo; most fossil mammals Darwin found in La Plata are related to S. American types; fossils in the caves of Brazil—same relationship.

• In 1839, Darwin strongly insisted on this “law of the succession of types, this wonderful relationship in the same continent between the dead and the living.’

• What does this law mean? It cannot be pretended that it is an immutable law that marsupials should have been chiefly or solely produced in Australia; for we know that Europe in ancient times was peopled by numerous marsupials

• On the theory of descent with modification, the great law of the long enduring, but not immutable, succession of the same types within the same areas is explained: the inhabitants of each quarter of the world will obviously tend to live in that quarter, during the next succeeding period of time, closely allied though in some degree modified descendants. If the inhabitants of one continent formerly differed greatly from those of another continent, so will their modified descendants still differ in nearly the same manner and degree.

But after very long intervals of time, and after great geographical changes, permitting much intermigration, the feebler will yield to the more dominant forms, and there will be nothing immutable in the distribution of organic beings