I believe they can be changes and revised
Answer:
Evolution is driven by rare mutations that occur in the DNA of organisms. These mutations could be lethal, neutral and some advantageous. The lethal mutations cannot exist in a population because the offspring is unable to survive to term in pregnancy or dies just after birth. The neutral are ones that do not considerably affect the organisms – though they could result in a disadvantage. The beneficial ones are the one that is kept in the population by natural selection because they confer an advantage e.g in the fight for resources or escaping predation and etcetera. Therefore, it's like a game of chances by nature. Paleontologists discover many species of organisms some of which are imperfect because nature produced them but they died off because their mutations gave them a disadvantage against better-adapted individuals.
The <em>Tiktaalik</em> fish from 375 million years ago became extinct because it did not well-developed eardrum for detecting vibrations in water which is significant in survival.
Dinosaurs during development of feathers had many imperfect species before the right wings for flight were conjured up by nature. An imperfect species is the <u><em>Tianyulong confucius</em></u> had stiff feathers that lacked vanes hence were not ideal for flight
