A large portion of our DNA is endogenous retroviruses, and it increase from say fish-amphibiam-lizard/snake-bird/dinasour(probably)-mammal-placental mammal-primate-human. It helps reshuffle DNA and insceases errors and mutations, which requires the development of better DNA repair functions to survive and increases the speed with which new adaptations emerge. Which is why say an alligator or a bird is pretty close to it's relatively distant ancestry and we're pretty different then our relatively close ancestry, with adaptations such as increase salt intake and decreased water requirements compared to chimps and banobos, nerve activated water grip mode for our digits, more efficient sweating for heat reduction and our very high endurance and more efficient bipedal walking, jogging and running.