Some theories can be proven and others cannot. I have not seen any hard evidence to date for the Theory of Evolution. It cannot be tested and proven. It starts with a premise of Belief in it, then from that platform, interprets science.
Gravity, however, can be tested and proven. There may be more to learn about it, and it may behave differently at times due to unknown causes, but in general it is easy to prove that gravity works.
I do think that gravity can change over time (as our planet ages and changes, also the universe) and this could affect previous theories pertaing to gravity and the way in which it operates.
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"Honey, would you buy me some boobles for my 40th b-day?" "No way, they're too expensive. Your own baubles will have to do."