This article gives students an idea about which groups of animals have the most complex brains and hearts and which don't. It also shows how these organs evolve from the lowly invertebrates up into the most complex vertebrates. It answers the questions students often have about whether all animals have a heart and a brain. It can also be used during evolution studies, especially when comparing anatomy as evidence for evolution. There are some thought-provoking questions at the end with an answer key.