All complex life on Earth is composed of nucleated cells, known as eukaryotic cells. The eukaryote arose only once, and bacteria normally show no tendency towards morphological complexity. The last common ancestor of eukaryotic cells was a chimera, formed in a unique union between two prokaryotic cells called endosymbiosis -- a non-Darwinian mechanism whereby organisms converge rather than diverge. Without that chimera, evolution may never have progressed beyond bacteria, and again none of us would be here.
Isn't is amazing how things just happen? Complexity beyond our comprehension magically arose, via some combination of mechanisms that we don't quite understand, but we know must have done the job. Our confidence is exceeded only by our lack of data.