From whence we don't know, but there is a lot of evidence for several competing theories (my favorite is the RNA world). If, once life arose, it did not attempt to survive, it would die off and not replicate. The organism with the will to survive is more likely to replicate -- in other words the survival instinct would become fixed quite rapidly in early life.
Do you actually try to mentally answer your own questions before you ask them, or are you simply transcribing the questions as they pop into your head? This is a very important question, and not meant to denigrate anyone, but I've noticed that "thinking several moves ahead" is not an artifact of the creationist crowd; it's as if contemplation of such concepts is rejected outright because of the implications it might raise.
"The evidence that is available at the present time does not support the idea that RNA, or an alternative replicator that uses the current set of RNA bases, was present at the start of life."
Shapiro, R., Prebiotic cytosine synthesis: A critical analysis and implications for the origin of life, Proc. Natl. Acad. Sci. USA 96(8):4396–4401, 1999
Cordially,