LUCA is a proposed point of convergence, not to be confused with circumstances prior to that point.
So while LUCA describes DNA as the hereditary material and so on, it is a well held notion that earlier thingy's and events may well have been of an RNA world.
http://en.wikipedia.org/wiki/RNA_world_hypothesis
As RNA has not only the ability to provide hereditary information, like DNA, but to be auto catalytic, like proteins.
But taking a step back, current hypotheis largely put extant hominids, of which there is only us, s having come from a remarkably small breeding population of some 600 individuals dating somewhere very roughly around 100k years ago.
But we have the bones, the lice, the tools and the art, from well before them, from erectus habilis and and so on.
When we look at that choke point, the 600 individuals or so from 100k years ago or so, it is not to say that that represents human evolution, from there forward, rather that for whatever reason what we have today genetically maps back to then and there, but does not speak at all towards the variety and disposition of any variety of other hominids.
LUCA says nothing about much before LUCA. To so concluse would be to look at us, look at our DNA, observe that we tracked back to about 600 folks about 100k years ago and say that there were not other homids ... "but I am not sure if there is evidence of that. I think not".
Obviously given the recency of hominids, we have evidence (bones), but I know of nobody that pretends that LUCA represented the first only novel event in any way shape form or matter. LUCA is simply a choke point, nothing extant is without travelling through LUCa lineaeg-wise, but certainly we agree their was homo habilis, homo erectus, etc all of which predated the hominid choke point of 100k years ago, the presence of the choke point says nothing about anything before it.
That requires independent direct evidence. 4 billion year old independent molecular evidence is hard to come buy, but again, I am aware of nobody that postulates that there were not a plethora of potential solutions of which one emerged as a consequence of drift and selection.
The notion that may have been many 'creation' events is easy to rationalize, more difficult is to explain why there is more than just one single life form. This massive statistical and selective tendency towards one would make LUCA early, and there is just no reasonable way around it.
Importantly, LUCA is not the original life form, it is the chock point through which all current life forms share a path. that is all, no more, no less.
My divergence from neanderthal predates my 100k yr old mandatory checkpoint for extant hominds, but that does not say there was never neanderthal or even vaguely suggest otherwise.
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