Yes, you have to be book smart, but not at the level most people think. You can't be re ed and get in, but it has more to do with being disciplined than book smart.
Being a Biology major or BioChem is not "easy," especially when you consider that to get into med school you have to make mostly A's. But that's where being disciplined comes in. It's about putting in the hours - something they'll have to be prepared for when they get to med school, where it's all about grinding.
HOWEVA, being able to use differential equations to do structural analysis (Civil Engineering) is a different type of "book smarts" than studying for biology tests and not missing any hw assignments. Few people will ever be able to do high level structural analysis, no matter how much they study. But I respect the hours med students put in to get through med school. Few people have that kind of discipline.
Yeah, that's why it helps big-time to have a list of impressive extracurriculars (if you're white).