The Edge sings like a siren. Sometimes the song is hauntingly close and constant. Sometimes it fades away for months. My main image of the Edge is from the topography of evolution. There is an edge beyond which an individual can neither survive nor reproduce successfully.
Timberline is one such example.
Zonations in tide pools are another. Evolution winnows out those individuals who stray beyond the edge. We are the descendants of those creatures that stayed on the right side of the edge. Our DNA has been strongly shaped to shape us to be sensitive to edges and stay within them. And so our DNA is rich with the inheritances of those who went across the edge.