The thing we know best is our self. We experience our own agency and will and "naturally" tend to ascribe agency and will to other people, animals, even inanimate objects. Our ancestors invested rocks, mountains, streams, clouds, and celestial objects with the attributes of life. Animism was the first philosophy.
A corollary of animism is artificialism: Whatever exists is the product of conscious design. The thunderbolt and the earthquake happen because someone makes them happen. Zeus hurling from on high, for example. Artifacts require artificers, Thus the spirit world, gods, God.
Piaget and others have shown that animism and artificialism are the default explanations of children, undoubtedly for the same reason they were the default explanations of humankind.
Beginning with the pre-Socratics, certain philosophers entertained another idea. Things happen not because of agency and will, but because they are constrained to happen by "natural laws." The search for these laws began with astronomy, and has been gradually extended to almost every area of human experience. As more and more phenomena were seen to act in accord with "the laws of nature," the spirit world was rendered largely superfluous. The naiads and dryads, the fairies, the mountain trolls, the angelic choirs who pushed the planets in their courses -- all sent packing.
Artificialism gave way to naturalism.
Have all phenomena been reduced to natural law? Of course not. Consciousness, the origin of life, the origin of the universe, the origin of the laws themselves continue to resist our probing, although remarkable progress has been made. Where natural explanations are not yet available, the naturalist will say "I don't know, let's continue probing." The artificialist will claim an artifact and presume an artificer. So-called intelligent design is the latest pseudoscientific manifestation of artificialism.
"I don't know" and "God did it" have exactly the same explanatory content: Zero. Yet the great majority of us continue to posit an artificer, and waste a huge amount of human energy championing one idea of the artificer over another.
Why not just let the distinction go. Instead of natural and artificial, how about known and unknown, or law and mystery. Look again at the diagram I posted yesterday. Even without understanding the biochemistry, how can anyone look at this diagram and not be struck dumb with awe, reverence, celebration, praise? The more we learn about the way the world works, the more we become aware of our ignorance. We are made no less ignorant by endowing our ignorance with personhood, agency and will.
Natural/artificial is one more outmoded duality -- like matter/spirit, body/soul, nature/supernature -- that explains nothing and makes life on a crowded planet fraught with disagreement.
(Tomorrow: Natural/artificial and the future of the Earth.)