Biologists can examine the sequence of base pairs in genes to map out their relationships with other genes, and in that way they can build a detailed map of which genes evolved from which other genes. What we find when we compare such maps among species is that they fit into a nice pattern of branching common descent. There are multiple other independent lines of evidence that also demonstrate not only branching descent but a reasonable overlap—the different lines of evidence generally agree about which species evolved into what, when.
