The Geographic Distribution Of Species Darwin thought up his Theory Of Common Descent because he had found biogeographic evidence. He thought that that evidence was much stronger than the fossil evidence.
Scientists still think so.
Basically, some species have suspicious resemblances to supposedly different species that just happen to live nearby. Often, it would be better design for them to instead resemble some further-away species. And, this is the norm. There are a huge number of good examples. The trees on the remote island of St. Helena are unlike the trees anywhere else on earth.