I believe that the presence/absence of interest can muddy the picture considerably. However, speaking specifically of ability, there is probably at most a weak positive correlation between the two. DH is a scientist (bio-chem area) who was not particularly strong in math while I have an undergraduate math degree but physics was the only science area in which I had any talent. Of course ability is relative and we had to "excel" in both math and science at the high school level to be competitive for the top colleges to which we applied.