The Origin of Species · Chapter
On the Absence or Rarity of Transitional Varieties explained
Darwin addresses the challenge of why transitional varieties are not commonly found in nature or the fossil record.
What happens
Darwin addresses the challenge of why transitional varieties are not commonly found in nature or the fossil record. He argues that natural selection, acting alongside extinction, tends to eliminate parent forms and intermediate links. The imperfection of the geological record, the historical fragmentation of continents, and the competitive advantage of more numerous forms over rarer intermediate varieties all contribute to the rarity of transitional forms. He concludes that species appear as well-defined entities because intermediate varieties are typically short-lived and supplanted.
Themes in this chapter
Natural Selection and the Struggle for Existence
Central to the chapter: natural selection drives extinction of parent and intermediate forms, shaping species boundaries.
Imperfection of the Geological Record
Key explanation for the absence of transitional fossils; the record is less complete than commonly assumed.
Characters to notice
- Charles Darwin
Author and primary narrator, presenting his theory and addressing difficulties.
- De Candolle
Cited for observations on the abrupt disappearance of alpine species.
- Edward Forbes
Referenced for similar observations in marine dredging.
- Mr. H. C. Watson
Provided information on the rarity of intermediate varieties.
- Asa Gray
Provided information on the rarity of intermediate varieties.
Key passages
“Thus extinction and natural selection go hand in hand.”
Extinction and natural selection are closely linked processes.
Highlights the core mechanism that eliminates transitional forms.
“The crust of the earth is a vast museum; but the natural collections have been imperfectly made, and only at long intervals of time.”
The Earth's crust is like a museum, but its fossil collections are incomplete and collected only at rare intervals.
Metaphor for the imperfection of the geological record.
“This difficulty for a long time quite confounded me.”
This problem puzzled me for a long time.
Darwin admits the challenge of missing intermediate varieties in continuous areas.