The Origin of Species · Chapter
On the Absence of Numerous Intermediate Varieties in Any Single Formation explained
Darwin argues that the geological record is extremely imperfect, explaining why we do not find numerous intermediate fossil links between species in any single formation.
What happens
Darwin argues that the geological record is extremely imperfect, explaining why we do not find numerous intermediate fossil links between species in any single formation. He notes that species may have existed elsewhere before appearing in a formation, that migration and geographical changes obscure transitions, and that the period of modification for a species is likely short relative to its total existence. He cites examples such as Trautschold's Ammonites and Hilgendorf's Planorbis multiformis as rare cases of gradual forms within a formation, and emphasizes that the chance of preserving a complete series of transitional varieties is very low.
Themes in this chapter
Imperfection of the Geological Record
Central theme of the chapter; Darwin explains why the geological record is incomplete and why we should not expect to find numerous transitional forms.
Extinction and the Succession of Forms
Discussed in relation to the appearance and disappearance of species within formations, and the role of migration and geographical changes.
Characters to notice
- Charles Darwin
Author and narrator; presents arguments on the imperfection of the geological record and the rarity of intermediate fossil varieties.
- Agassiz
Mentioned as a naturalist who maintains that tertiary species are specifically distinct from living ones, despite slight differences.
- Pictet
Mentioned alongside Agassiz for holding that tertiary species are distinct from recent species.
- Dr. Falconer
Cited for the insight that the period of modification for a species is probably short compared to its period of stasis.
- Sir John Lubbock
Quoted for the statement that 'Every species is a link between other allied forms.'
- Bronn
Mentioned as a palaeontologist who concluded that the average duration of each formation is twice or thrice as long as the average duration of specific forms.
Key passages
“If then there be some degree of truth in these remarks, we have no right to expect to find, in our geological formations, an infinite number of those fine transitional forms, which, on our theory, have connected all the past and present species of the same group into one long and branching chain of life.”
Given these points, we should not expect to discover countless subtle transitional fossils in geological strata, even though our theory suggests that all past and present species are linked in a continuous branching chain.
Darwin justifies the absence of intermediate fossils by the imperfection of the record.
“It is a more important consideration, leading to the same result, as lately insisted on by Dr. Falconer, namely, that the period during which each species underwent modification, though long as measured by years, was probably short in comparison with that during which it remained without undergoing any change.”
A key point, emphasized by Dr. Falconer, is that the time a species spends changing is brief relative to the time it stays stable, making transitional forms even harder to capture in the fossil record.
Darwin uses Falconer's insight to support the rarity of intermediate fossils.
“We may safely infer that with marine animals of all kinds there has been a large amount of migration due to climatal and other changes; and when we see a species first appearing in any formation, the probability is that it only then first immigrated into that area.”
For marine animals, migration driven by climate and other factors is common, so a species' first appearance in a formation likely indicates its arrival there rather than its origin.
Darwin explains that apparent first appearances may be due to migration, not evolution.
