The Origin of Species · Chapter
Geographical Distribution explained
Darwin argues that each species originates from a single location and then migrates as far as its capabilities and past conditions allow.
What happens
Darwin argues that each species originates from a single location and then migrates as far as its capabilities and past conditions allow. He explains that barriers, such as oceans, prevent migration and thus account for distinct faunas, while continuous landmasses or former land bridges explain similarities between distant regions. He extends this reasoning to account for the relationships between species in the northern and southern hemispheres, particularly in light of past climatic changes like the Glacial and Pliocene periods.
Themes in this chapter
Geographical Distribution and Barriers
The chapter focuses on how barriers like oceans and climate zones shape the distribution of species, and how migration from a single centre explains both similarities and differences across regions.
Common Descent and the Tree of Life
Darwin argues that species of the same genus descend from a common progenitor, and that migration with modification explains the relationships between species in different areas.
Extinction and the Succession of Forms
The discussion of past climatic changes and the migration of species implies that older forms have been replaced or modified over time, linking to patterns of extinction and succession.
Characters to notice
- Charles Darwin
Author and narrator; presents the argument for single centres of creation and subsequent migration.
- Mr. Wallace
Darwin references Wallace's conclusion that every species has come into existence coincident with a preexisting closely allied species, supporting descent with modification.
- Asa Gray
Mentioned as having shown that more plants are identical between the New and Old Worlds than was formerly supposed.
- James Dwight Dana
Cited for his work on crustaceans, showing closely allied forms in the Mediterranean and seas of Japan.
- Edward Forbes
Darwin mentions Forbes's view on the migration of species during the Glacial period and extends it.
Key passages
“On this principle of inheritance with modification we can understand how it is that sections of genera, whole genera, and even families, are confined to the same areas, as is so commonly and notoriously the case.”
The idea of inheritance with modification explains why groups of related species are often found only in specific regions.
Darwin links geographical distribution to common descent.
“The great and striking influence of barriers of all kinds, is intelligible only on the view that the great majority of species have been produced on one side, and have not been able to migrate to the opposite side.”
Barriers make sense only if most species originate on one side and cannot cross to the other.
Barriers are key evidence for single centres of creation.
“If the existence of the same species at distant and isolated points of the earth’s surface can in many instances be explained on the view of each species having migrated from a single birthplace; then, considering our ignorance with respect to former climatical and geographical changes, and to the various occasional means of transport, the belief that a single birthplace is the law seems to me incomparably the safest.”
If we can explain how species reach distant places by migration from one origin, then the safest conclusion is that each species has a single birthplace.
Darwin defends the single-centre hypothesis against multiple-creation views.