Because DNA is universal to all life, its presence strongly suggests that all creatures on Earth evolved from a common ancestor.
It also explains how the proliferation of genetic mutations, combined with the processes of natural selection, enables evolution to happen. Ultimately, DNA is the engine that drives evolution. It’s an elegant process that doesn’t require a guiding hand.
Scientists can now examine the DNA from different species of organism and use the data produced to see how closely related the two species are to each other. By collecting a lot of this data, scientists can compare the results with conventional ideas about how organisms have evolved. What they found was that DNA data supported the conventional theory of evolution.