DNA supports evolution because all life on Earth carries DNA, and evolution happens only after DNA changes. These changes are called mutations and happen spontaneously from flawed DNA copying or from mutagens, such as X-rays or chemicals.
All life carries the same DNA components, and scientists have found the same DNA sections in bacteria as in humans. Biologists have put patches of DNA controlling one part of an animal into another animal to find that it performs the same job. For example, a DNA section that controls how eyes are formed in mammals like mice was put into a fly, and it produced a normal eye.
Further evidence for how DNA supports evolution is reflected in closely related organisms. The closer the relation, the more similar their DNA. The DNA sequences of humans and chimpanzees are about 97 percent identical.
Mutations affect evolution positively, negatively or not at all. Beneficial mutations aid survival. For example, the white fur of polar bears gives them an advantage in hunting seals. Deleterious mutations hurt survival. For example, lions born with weak hearts do not survive long enough to pass on their genes.
Environment determines whether mutations are advantageous. Deleterious mutations can become beneficial and vice versa. For example, hornless rhinoceroses were once at a defense disadvantage. However, hornless rhinoceroses are evolving due to pouching. Neutral mutations are neither beneficial or deleterious, but can always change in either direction. The bottom line is that evolution only happens when living things survive long enough to pass on their viable DNA to future generations.