Embryology, cell biology, bone structure, physiology, fossil records. That's just a few way evolution has been supported. Embryology: almost all embryos are Identical in early development Cell biology: all eukaryotic cells under go cellular respiration and other identical functions Bone structure: look at different skeletons of mammals, they all have strong resemblances of one another. Even a whale and a human Physiology: all mammals have neurons and muscle cells that go through the same cellular pathways as humans along with peristalsis and other physiological functions. Fossil records: speaks for it's self.