Will and would are all but interchangeable here. Would only “feels” like it fits better because it’s a hypothetical event, but it’s a cause and effect being talked about. Well, effect and cause but the point stands.
Edit: I’d like to point out that “will” is future tense, and “would” is past tense.
You don’t think house cats existed before DDT pesticides?
You don’t think house cats, which have existed for 3600 years, existed before 1874?…
Do I need to math that math for you?