[AndrewC]

In the language analogy the analogues are biological organisms and languages not languages and natural selection.

Well, this is what he states.

but an illustration of some analogous processes in a different field: linguistics

[b_sharp]

"Natural languages (excluding deliberately-crafted artifacts such as Esperanto) undergo constant evolution in words, meanings and structures which may be analogous, in many particulars, to the processes described by biological evolution."

I think if you consider the above sentence carefully you will see that Toryheartland is referring to the evolutionary change in words as a process that is analogous to the processes in biological evolution. It is the morphology, the words and sentence structure, that is undergoing change just as the morphology of biological organisms undergo change. The meaning of the words is not the process but the target of the process.