# Effects of the Increased Use and Disuse of Parts, as Controlled by Natural Selection explained — The Origin of Species

> Chapter companion for The Origin of Species by Charles Darwin.

## What happens

Darwin examines how the increased use or disuse of body parts, combined with natural selection, can lead to structural modifications. He discusses examples such as flightless birds, wingless beetles on Madeira, and blind cave animals, arguing that disuse gradually reduces organs while natural selection may further refine or eliminate them, and that these changes are inherited.

## Themes in this chapter

### Natural Selection and the Struggle for Existence

Natural selection is shown to act alongside disuse, e.g., in the reduction of wings in Madeira beetles and the loss of eyes in cave animals.

### Adaptation and the Utilitarian Doctrine

Structures are modified or lost based on utility; disuse and natural selection together produce adaptations to specific environments.

## Character check-ins

### Charles Darwin

Author and narrator; presents arguments and observations on use and disuse.

### Professor Owen

Quoted regarding the anomaly of flightless birds.

### Mr. Wollaston

Discovered the high proportion of wingless beetles on Madeira and provided key observations.

### James Dwight Dana

Provided information on affinities of American cave animals.

### Agassiz

Noted the anomalous nature of blind cave fish such as Amblyopsis.

## Key lines

> As Professor Owen has remarked, there is no greater anomaly in nature than a bird that cannot fly; yet there are several in this state.

Professor Owen noted that flightless birds are a striking anomaly, yet several exist.

_Introduces the paradox of flightless birds as evidence for disuse._

> Mr. Wollaston has discovered the remarkable fact that 200 beetles, out of the 550 species (but more are now known) inhabiting Madeira, are so far deficient in wings that they cannot fly; and that, of the twenty-nine endemic genera, no less than twenty-three have all their species in this condition!

Mr. Wollaston found that 200 of the 550 beetle species on Madeira have reduced wings and cannot fly, and 23 out of 29 endemic genera are entirely wingless.

_Key evidence for natural selection favoring reduced flight in island beetles._

> By the time that an animal had reached, after numberless generations, the deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and natural selection will often have effected other changes, such as an increase in the length of the antennae or palpi, as a compensation for blindness.

After many generations in deep caves, disuse would have nearly eliminated eyes, and natural selection would have favored compensatory changes like longer antennae or palpi.

_Explains the combined role of disuse and natural selection in cave animal adaptations._

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