" Life on our planet is several billion years old, and we literally embody this deep history in our structures, our behaviors, our instincts, our genes. We humans retain, for example, the remnants of gill arches, much modified, from our fishy ancestors and even the neural systems that once controlled gill movement. As Darwin wrote in The Descent of Man, “Man still bears in his bodily frame the indelible stamp of his lowly origin.” We bear, too, an even older past; we are made of cells, and cells go back to the very origin of life. "

― Oliver Sacks , The River of Consciousness