Like many scientists of his day, Darwin included, Haeckel didn’t get everything right, as one would expect from a work written prior to a thorough understanding of DNA, relativity, or quantum mechanics. Nevertheless, his fundamental philosophical arguments remain valid. One antiquated idea that’s examined in-depth in both works is the concept of “ether”, a term used to describe the medium which exists between the particles of matter in the universe. In the post-Einstein world, this ether could be seen as the very fabric of space-time itself. Nowadays, ether might even be analogous to dark matter. The point is, even though all of Haeckel’s scientific conclusions may not have survived the scrutiny of the past century, it doesn’t change the fact that his application of empirical science to the philosophical questions of the nature of the universe, God, human consciousness, and free will still provides thought-provoking inspiration for rational thinkers looking for answers to such universal riddles.