Humans Smell Worse
Well, we don't exactly smell worse, not in the hold-your-nose sense. But there's reason to think our sense of smell has ossified: Unlike most animals, we no longer rely on that sense to make crucial everyday decisions (although it does seem that the ability to smell potential mates with compatible immune system profiles is still active.)
Just as cave-dwelling fish gradually lose their no-longer-necessary sense of sight, evidence suggests that mutations impairing our sense of smell have accumulated in human genomes.
Image: Mark Rosenwald/Flickr