Re-read the link in post one. Nowhere does it say that Harvard (or any other college) expects/wants you to double up on anything. Whether you choose to do so is limited, in part, to course offerings and graduation requirements. Whether you get into any school will not be determined by whether or not you doubled up in a subject. But as a potential history major, I see no need to double up in math and/or science. If you were able to double up, it would make more sense to do so in history/social sciences.