The evolution of species from a common ancestor through a Darwinian process is believed in, not so much because of evidence or lack of it, but because materialism/physicalism demands it. The emotional attachment we see among believers in this theory is surprising, to say the least, and reflects how important their belief in materialism is to their sense of identity and their place in the world. This emotional attachment is so strong that just by making a seemingly innocuous statement questioning the validity of Darwinism many materialists will become quite enraged. This shows the lack of rationality they possess on this issue which hampers their ability to see clearly and come to a considered view.
Watch Richard Dawkins (a believer in Darwinian Evolution) interviewing Wendy Wright (a Creationist) and watch his emotional response to her dissenting view.