It is commonly believed that art imitates nature, which was Aristotle's position. To avoid the trap of thinking that Aristotle meant art is merely a copy of the outside world, we need to know that the ancient Greeks distinguished between nature as a pre-given state and nature as a creative principle. If we take the latter meaning, we see art as a creative force, like nature, making new objects in the world that were not there before. They are a 'completion of nature'. (Blumenberg p 55-6)
The other meaning of copying things in the world outside is unsustainable in modern times as art may be derived from many things including other art rather than any natural condition. We now draw a picture, not something that it represents.
Aristotle gives the example of designing and building a house (for the Greeks the idea 'technic' included art) as being how nature would have done it if 'growing' a house had been required.
Art is then what nature would have done if it had needed to. Instead human artists extend the existing using aesthetic principles, completing not copying the work of nature.