The Origin of Species · Chapter
On the Origin and Transition of Organic Beings with Peculiar Habits and Structure explained
Darwin addresses objections to his theory by examining transitional forms and habits, using examples such as the Mustela vison, flying squirrels, Galeopithecus, woodpeckers, petrels, and water-ouzels to argue that natural selection can grad
What happens
Darwin addresses objections to his theory by examining transitional forms and habits, using examples such as the Mustela vison, flying squirrels, Galeopithecus, woodpeckers, petrels, and water-ouzels to argue that natural selection can gradually modify structures and behaviors. He emphasizes that habits can change without corresponding structural changes, and that intermediate grades exist in nature, supporting the idea of descent with modification.
Themes in this chapter
Natural Selection and the Struggle for Existence
Darwin uses examples of transitional habits and structures to illustrate how natural selection can gradually modify organisms to fit new ecological niches.
Adaptation and the Utilitarian Doctrine
The chapter emphasizes that each structure is useful to its possessor in its environment, and that changes in habits or structure are driven by utility in the struggle for life.
Characters to notice
- Charles Darwin
Author and narrator, presenting arguments and observations on transitional habits and structures.
- Sir John Lubbock
Cited for discovering the aquatic habits of the hymenopterous genus Proctotrupes.
- Mr. Hudson
Referenced for observations on the woodpecker Colaptes campestris in certain districts.
- Audubon
Mentioned as the only observer who has seen the frigate-bird alight on the ocean surface.
- Mr. Gould
Referenced for observations on the logger-headed duck (Micropterus of Eyton).
Key passages
“It would be easy to show that there now exist carnivorous animals presenting close intermediate grades from strictly terrestrial to aquatic habits; and as each exists by a struggle for life, it is clear that each must be well adapted to its place in nature.”
There are living carnivores that show a continuous range from fully land-based to fully water-based lifestyles, and because each survives through competition, each is clearly suited to its specific role in the environment.
Darwin uses the Mustela vison as an example of intermediate habits.
“Look at the family of squirrels; here we have the finest gradation from animals with their tails only slightly flattened... to the so-called flying squirrels...”
Consider squirrels: there is a perfect series from those with barely flattened tails to those that glide using a broad membrane, showing how natural selection can produce a flying squirrel.
Darwin illustrates gradual structural change leading to new capabilities.
“He who believes in the struggle for existence and in the principle of natural selection, will acknowledge that every organic being is constantly endeavouring to increase in numbers; and that if any one being varies ever so little, either in habits or structure, and thus gains an advantage over some other inhabitant of the same country, it will seize on the place of that inhabitant...”
Anyone who accepts natural selection and the struggle for life will recognize that all organisms strive to multiply, and if a small variation in habit or form gives an edge over a competitor, that organism will take over that competitor's role.
Darwin explains how new habits and structures can arise through competition.
“Can a more striking instance of adaptation be given than that of a woodpecker for climbing trees and seizing insects in the chinks of the bark? Yet in North America there are woodpeckers which feed largely on fruit, and others with elongated wings which chase insects on the wing.”
What better example of adaptation exists than the woodpecker's tree-climbing and insect-catching abilities? Yet some North American woodpeckers eat mostly fruit, and others have long wings to catch insects in flight.
Darwin shows that even highly specialized structures can be modified for different habits.
