Plot: Today we're going to take a closer look at brains, how animals use them, and how some animals have even evolved to lose them! It turns out a brain (and intelligence more broadly) isn't easy to define, but what we do know for sure is that brains have evolved over time in response to the challenges in an animals' environment. And what we'll find is that sometimes it's much smarter to have a tiny, simple brain than a big, complicated one!