Ed Yong in The Atlantic:
Today, if you wanted to talk about something that’s clear, you’d say that it has clarity. But if you were around in 1890, you would almost certainly have talked about its clearness.
Plotkin first noticed this linguistic change while playing with Google’s Ngram Viewer, a search engine that charts the frequencies of words across millions of books. The viewer shows that a century ago, clearness dominated clarity. Now the opposite is true, which is strange because clarity isn’t even a regular form. If you wanted to create a noun from clear, clearness would be a more obvious choice. “Why would there be this big upswing in clarity?,” Plotkin wondered. “Is there a force promoting clarity in writing?”
It wasn’t clear. But as an evolutionary biologist, Plotkin knew how to find out.
The histories of linguistics and evolutionary biology have been braided together for as long as the latter has existed. Many of the earliest defenders of Darwinism were linguists who saw similarities between the evolution of languages and of species. Darwin himself wrote about these “curious parallels” in The Descent of Man. New words and grammatical rules are continually cropping up, fighting for existence against established forms, and sometimes driving those old forms extinct. “The survival … of certain favored words in the struggle for existence is natural selection,” Darwin wrote.
More here.