OP asked wikipedia in the wrong place. https://en.wikipedia.org/wiki/Natural_science#History

As one can remember from high school, natural science fields spawned from natural philosophy from 17th through 19th century. Culminating maybe with psychology in the early 20th century (end of 19th). No mystery there.

I was perfectly aware of this, and checked https://en.wikipedia.org/wiki/Natural_philosophy . The link and quote I provided are much more directly relevant. Ph.D.s aren't just for natural science; they're for everything that isn't covered by a J.D. or an M.D. Funny coincidence, that, given the historical factoid "All fields other than theology, law, and medicine were traditionally known as philosophy".

Ph.D.s in literature, history, or classics have nothing to do with natural philosophy, and never did.

Problem, probably, arises in dual definition of philosophy. Google says (define: philosophy):

(this is the classic meaning) 1. the study of the fundamental nature of knowledge, reality, and existence, especially when considered as an academic discipline.

2. a theory or attitude that acts as a guiding principle for behaviour.