The foundations of The origin of species : a sketch written in 1842 / edited by Francis Darwin.
- Charles Darwin
- Date:
- 1909
Licence: Public Domain Mark
Credit: The foundations of The origin of species : a sketch written in 1842 / edited by Francis Darwin. Source: Wellcome Collection.
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![The first fact geology proclaims is immense number of extinct forms, and new appearances. Tertiary strata leads to belief, that forms gradually become rare and disappear and are gradually sup¬ plied by others. We see some forms now becoming rare and disappearing, we know of no sudden creation: in older periods the forms appear to come in suddenly, scene shifts: but even here Devonian, Permian &c. [keep on supplying new links in chain]—Genera and higher forms come on and disappear, in same way leaving a species on one or more stages below that in which the form abounded. (Geographical Distribution.) § vi. Let us consider the absolute state of dis¬ tribution of organisms of earth’s face. Referring chiefly, but not exclusively (from difficulty of transport, fewness, and the distinct characteristics of groups) to Mammalia; and first considering the three or four main [regions] divi¬ sions; North America, Europe, Asia, including greater part of E. Indian Archipelago and Africa are intimately allied. Africa most distinct, especially most southern parts. And the Arctic regions, which unite N. America, Asia and Europe, only separated (if we travel one way by Behring’s St.) by a narrow strait, is most intimately allied, indeed forms but one restricted group. Next comes S. America,—then Australia, Madagascar (and some small islands which stand very remote from the land). Looking at these main divisions separately, the organisms vary accord¬ ing to changes in condition1 of different parts. But besides this, barriers of every kind seem to separate 1 In the Origin, Ed. i. p. 346, vi. p. 493, the author begins his discussion on geographical distribution by minimising the effect of physical conditions. He lays great stress on the effect of barriers, as in the present Essay.](https://iiif.wellcomecollection.org/image/b31351761_0063.jp2/full/800%2C/0/default.jpg)
