The code that is DNA

[Mister Agenda]

I emphasize once mostly because evolution always attempts to trace ancestry to a single common ancestor for all life. Rarely do you hear someone suggest multiple lineages emerging from separate origins of life.

That's because we haven't found any evidence that suggests multiple lineages. It's no problem for the theory of evolution if another lineage were discovered, as long as it follows the same biological rules as the one lineage we know of. Yes, there may be multiple lineages, but that suggestion has little value if we can't find them. It's possible that life started more than once but only one lineage survived the early stages. We just don't have any evidence/observations to support that hypothesis. It's easy to imagine a 'first come, first served' scenario though, where once even microbial life becomes abundant, any life in the early stages is simply devoured unless it's completely isolated from already extant life.