The Origin of Species · Chapter
Species of the Larger Genera in Each Country Vary More Frequently Than the Species of the Smaller Genera explained
Darwin presents statistical evidence from floras and insect collections showing that species belonging to larger genera (those with many species) tend to vary more frequently and produce more varieties than species in smaller genera.
What happens
Darwin presents statistical evidence from floras and insect collections showing that species belonging to larger genera (those with many species) tend to vary more frequently and produce more varieties than species in smaller genera. He interprets this as supporting his view that species are strongly marked varieties, and that active 'manufactories' of species continue to produce incipient species where many have already formed.
Themes in this chapter
Variation and Inheritance
Darwin uses the frequency of varieties in larger genera to argue that variation is ongoing and that species are incipient varieties.
Natural Selection and the Struggle for Existence
The chapter links active variation in large genera to the ongoing process of natural selection, where incipient species are formed.
Characters to notice
- Charles Darwin
Author and narrator, presenting statistical tables and reasoning on variation in larger versus smaller genera.
Key passages
“From looking at species as only strongly marked and well-defined varieties, I was led to anticipate that the species of the larger genera in each country would oftener present varieties, than the species of the smaller genera; for wherever many closely related species (i.e., species of the same genus) have been formed, many varieties or incipient species ought, as a general rule, to be now forming.”
Because Darwin views species as just strongly marked varieties, he expects that genera with many species will also have many current varieties, since active formation of species implies ongoing variation.
Core logical link between species as varieties and the observed pattern of variation in large genera.
“Where many large trees grow, we expect to find saplings. Where many species of a genus have been formed through variation, circumstances have been favourable for variation; and hence we might expect that the circumstances would generally still be favourable to variation.”
Just as a forest with many mature trees likely has many young saplings, a genus with many species likely still has favorable conditions for producing new varieties.
Analogy illustrating the expectation of ongoing variation in large genera.