DNA differences among species is relative to the time they diverged on the tree of life. Molecular confirmation Since 1859, that great tree has been built up painstakingly by close study of fossils and modern organisms. Proteins in the bodies of all organisms, and indeed DNA and RNA, the fundamental molecules of life, carry records of evolutionary transitions. So, humans have molecules that are nearly identical to those of chimpanzees, rather more different from those of cows, and very different from those of slime molds. The amount of difference is proportional to the time of divergence on the evolutionary tree.
Molecular biology confirms evolutionary transitions.
Since 1960, molecular biologists have been drawing up their own evolutionary trees, and these match those based on fossils and museum specimens of living plants and animals. The final, and most startling, confirmation of Darwin's insight also comes from the molecular biology. Conclusion Evolutionary transitions are demonstrated by so-called 'missing links', fossils like Archaeopteryx, and the whole array of intermediates between dinosaurs and modern birds that lie on either side of it. There are thousands of other fossils that plug the gaps between modern groups that are quite separate, and new finds every year plug yet more gaps. The shapes of evolutionary trees have now been confirmed from independent evidence of molecular structures.