The Origin of Species · Chapter
On the Inhabitants of Oceanic Islands explained
Darwin examines the distribution of species on oceanic islands, arguing that the scarcity of species, high proportion of endemic forms, and peculiarities of flora and fauna are best explained by descent with modification and limited immigra
What happens
Darwin examines the distribution of species on oceanic islands, arguing that the scarcity of species, high proportion of endemic forms, and peculiarities of flora and fauna are best explained by descent with modification and limited immigration rather than independent creation. He discusses how ease of immigration, intercrossing with unmodified immigrants, and natural selection shape insular populations.
Themes in this chapter
Geographical Distribution and Barriers
Darwin uses oceanic islands to illustrate how isolation and barriers affect species distribution, endemism, and modification.
Adaptation and the Utilitarian Doctrine
Discusses how hooked seeds become useless appendages on mammal-free islands, and how herbaceous plants may evolve into trees when competing on islands.
Characters to notice
- De Candolle
Cited for admitting that oceanic islands have fewer plant species than continental areas, and for noting that trees generally have confined ranges.
- Mr. Wollaston
Cited for admitting that oceanic islands have fewer insect species than continental areas.
- Dr. Hooker
Referenced for showing that in the Galapagos Islands the proportional numbers of different plant orders differ from elsewhere.
Key passages
“The species of all kinds which inhabit oceanic islands are few in number compared with those on equal continental areas: Alph. de Candolle admits this for plants, and Wollaston for insects.”
Oceanic islands have fewer species than similar-sized continental areas, as noted by de Candolle for plants and Wollaston for insects.
Highlights the general scarcity of species on islands.
“He who admits the doctrine of the creation of each separate species, will have to admit that a sufficient number of the best adapted plants and animals were not created for oceanic islands; for man has unintentionally stocked them far more fully and perfectly than did nature.”
If each species were separately created, one would have to conclude that the creator failed to provide enough well-adapted species for oceanic islands, since humans have accidentally introduced more species than nature did.
Argues against independent creation by pointing out human-mediated introductions.
“Again, islands often possess trees or bushes belonging to orders which elsewhere include only herbaceous species; now trees, as Alph. de Candolle has shown, generally have, whatever the cause may be, confined ranges.”
Islands frequently have trees from plant groups that are normally herbaceous on continents; de Candolle noted that trees tend to have limited geographic ranges.
Explains how herbaceous plants may evolve into trees on islands due to lack of competition.