When we learned how to stop the aging process, that was a major step. That's what turned us into different animals. But that wasn't evolution; that was science. We became more like permanent fixtures. Reproduction lost it's urgency. The priority became creating a perfectly sustainable, perfectly safe existence. For the most part, we became plants.
But there were some, a very few, that rejected the eternal boredom of immortality. They clung to short lives of joy, pain, growth and inevitable death. They were the ones that evolved. The rest of us were just people, but they called themselves Humans.
People crowded the planet. We were everywhere. Huddled in our safe existences like fungus under rocks, never risking any danger. Humans, in contrast, mastered the planet. They explored the depths of the seas, and conquered every mountain top. They orbited the Earth, and colonized the moon, then Mars. Many of them died, but they reproduced with voracious passion. Before long, they were pushing out to explore deep space. That's when the real evolution started.
As people on Earth we lived eternally, but we never changed much. Our bodies were our prized possessions. We nurtured them with great care, feeding them with the healthiest foods, and exercising them until they were sculptures of fitness. They were our eternal vessels. We found it increasingly difficult to relate to the Humans. They treated their bodies like tools. They injured themselves recklessly in wild adventures. For the most part we lost track of them as they branched out and explored countless different environments. When one group of them returned a couple of thousand years later, we didn't recognize them.
After living in deep space, their descendants had lost most of their musculature. Their small thin bodies had pale, almost white skin. The darkness of space had caused their eyes to become huge and black, and their heads looked disproportionately large. They just looked so... alien.