To me they also represent the four states of matter: Solid, Liquid, Gas and Plasma.
The ancients classified all things by their elements and we can do likewise with the states of matter. Often there is the thought that we are more advanced and more intelligent than those in antiquity. We scoff at the things they believed, their theories of the world, because we know so much better.
I don't think that's the case. Our brains aren't much different than they've ever been, so our potential for creativity and intelligence aren't any greater than the ancients'. I think the difference is our access to shared knowledge. We've never relied on just our own brains to retain all the information necessary to our lives.
Our ancestors were smart - We are smart - Our descendants will be smart