The Origin of Species · Chapter
Specific Characters More Variable Than Generic Characters explained
Darwin argues that specific characters (traits distinguishing species within a genus) are more variable than generic characters (traits common to all species of a genus).
What happens
Darwin argues that specific characters (traits distinguishing species within a genus) are more variable than generic characters (traits common to all species of a genus). He explains this by noting that generic characters are inherited from a common ancestor and have remained stable over long periods, while specific characters have diverged more recently and thus are still prone to variation. He contrasts this with the creationist view, which offers no explanation for such patterns.
Themes in this chapter
Variation and Inheritance
Darwin uses the differential variability of specific versus generic characters to illustrate how inheritance from a common ancestor shapes patterns of variation.
Common Descent and the Tree of Life
The explanation that generic characters are inherited from a common progenitor and specific characters have diverged more recently directly supports the concept of common descent.
Characters to notice
- Geoffroy Saint-Hilaire
Cited regarding the correlation between normal differences among species and the frequency of anomalies in individuals.
Key passages
“It is notorious that specific characters are more variable than generic.”
It is well known that traits distinguishing species are more prone to variation than traits shared by all species in a genus.
Darwin establishes the central observation of the chapter.
“On the ordinary view of each species having been independently created, why should that part of the structure, which differs from the same part in other independently created species of the same genus, be more variable than those parts which are closely alike in the several species? I do not see that any explanation can be given.”
If each species were separately created, there is no reason why the parts that differ between species should be more variable than the parts that are similar. No explanation is possible under that view.
Darwin highlights the explanatory failure of creationism regarding variability patterns.
“But on the view that species are only strongly marked and fixed varieties, we might expect often to find them still continuing to vary in those parts of their structure which have varied within a moderately recent period, and which have thus come to differ.”
If species are just well-defined varieties, we should expect them to keep varying in the traits that have recently changed and caused them to diverge.
Darwin presents his evolutionary explanation for the greater variability of specific characters.