I totally agree with the idea of learning for the sake of learning (I come from a school that doesn't show you your grades), and I'm not sure how my response indicated the contrary. My point is that if you are learning for the sake of learning, you do not need a second degree just to prove you are smart. You can accomplish nearly an equivalent amount of learning without the official 2nd major, or even more so, because you can take a wider variety of social science classes, for instance, instead of just history classes. So like, instead of having to take 8 history classes, the OP could take 4 history classes, 2 economics classes, and 2 political science classes, for example. No 2nd degree, but a wider area of knowledge.
My perspective is probably different, though, because I go to a liberal arts school that has a required year long humanities course, and a ton of area requirements, so everyone graduates with a pretty well rounded education. So if anything, the second degree to me seems like you're cramming stuff in to seem more impressive. But maybe at most other colleges, if you only major in biology, that may mean you don't really get the chance to get a good social science/humanities background unless you double major?