Why should there be a numerical parameter predictably increased by evolution? Why not look for a numerical parameter predictably increased by continental drift? or by prayer? by ostriches?
One of the key pieces of justification for FAI is the idea of "optimization process". Evolution is given as an example of such process, unlike continental drift or ostriches. It seems natural to ask what parameter is optimized.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.