Your post reminds me a bit of an anime I recently watched called Gargantia. In a desperate bid to explore and colonize the unknown reaches of space, humankind separated along two very different evolutionary paths, one completely alien from the original form. The humans which stayed behind on Earth learned to coexist with this knew form of human life they affectionately named Whale Squid. They had no idea the Whale Squid were once human, and they venerated them as sacred animals. The humans in space, however, did not resolve their differences peacefully and began an arms race against this new form of life. It was fascinating to say the least.