Answer:
Biologists often compare the sequences of related genes. If two species have the similar gene, it is because they inherited it from a common ancestor. In general, the more the DNA differences in homologous genes between two species, the more distantly the species are related.
Because there are tens of thousands of genes in humans and other organisms, DNA contains a tremendous amount of information about the evolutionary history of each organism. It determines evolutionary relationships among organisms, and it indicates the time in the past when species started to diverge from one another.
