Or it could go back even further than that. Back to the reason humanity left Kobol in the first place and formed the 13 colonies.
I've been pondering this conundrum ever since these four realized they were Cylons. Especially in Sol's (Col. Tigh) case, as he was a soldier (adult) during the first Cylon War over 40 years ago. And as we learned in Razor the Cylons were only then experimenting with cybernetic hybrids at the time. So if the Cylons were only experimenting in cybernetic life at the time of the first Cylon War, then were does Col. Tigh come from?
What we do know matter of fact, is that there are twelve models. We have at one point or another over the past three seasons been introduced to the first six models. Then we find out that Starbuck, Anders, Col. Tigh, Tory and Tyrol are also Cylons. Which brings us up to 11 models - or maybe 10 models, as I am not yet 100% convinced that Starbuck is a Cylon (more on that later). So we have at least 10 to 11 known models of hybrid Cylons. The obvious question is who is/are the final model(s) and where do they all come from, as Col. Tigh (who's at least 60) is evidence the Cylons have been around a lot longer than 40 years.
The other big question on my mind. Does that mean either Bob Dylan or Jimi Hendrix are Cylons too. Yeah, I know the question sounds very silly, but think about it. Tory, Anders, Tyrol and Col. Tigh all heard All Along the Watchtower in their heads. I've heard the song so much in my life, that I knew exactly what it was the very first time they started hearing the weird half-melodies in their heads. Bob Dylan is the writer/singer of the original version of the song, and Jimi Hendrix's version of Watchtower made the song a global, household fame. If you knew the story of how Jimi came to rerecord Watchtower, it would have you wondering too. I ask the question about Bobby and Jimi simply because the song does exists, it is a real song, and the last I heard, it originated on Earth - the place where the Galactica and crew are trying to get too (and probably will succeed in season four). So what awaits our heroes when they get to Earth? Are the Cylons already here, and we just do not know? And if they are already here, what have they been up to all these millenia.
I think some of the clues of what is to come lie in the original BSG series. The new series has been savvy enough to draw many parallels without ripping off the original - they've managed to make it there own without denying the roots of the new program. However, in the original BSG, the Cylons were a race of sentient reptiles on the verge of complete extinction. Matter of fact, in the first half of the season (before Baltar is given his own Base Star), you occasionally get to see the last of the Cylons. The robotic Cylons from the original series were built as servants to the reptilian species and to carry on their legacy after they were gone. While I do not feel the new series will resurrect the idea of the reptilian Cylon species, I do feel they are going to reveal the Cylons (robotic species), like their reptilian counterparts from the original series, are much, much older than humanity and were a space faring species long before humanity was.
So how does this cybernetic Cylon species evolve into the Cylons we know from the show? Mass Effect. It's this videogame on the Xbox 360, but the story within holds a clue. You have an older cybernetic species (the original Cylons) and maybe it is nothing more than a probe, but it comes into contact with another almost sentient cybernetic species (the robotic servents that the 12 Colonies created as servants), wires get crossed and POW, you have a new species of Cylons (neo-Cylons) who are for whatever reason, jealous of their human masters; or maybe not jealous at all. Perhaps the humans refused to acknowledge the new born sentience of this new species, forcing the neo-Cylons to fight a war for their freedom. Afterall, it is one thing just to talk about giving up slave labor, but depending on how extensive the use of slaves is embedded in a society, giving up slave labor is potentially devastating to the economy. So the colonists have every reason in the world not to want to believe their robotic slaves suddenly evolved sentience, and as such, are endowed to all the same rights and responsibilities as their (former) masters. So you have the first Cylon War. On a side not (here comes the useless trivia), the origins of the word robot, if I remember correctly is "robos" which is Scandinavian for slave. Anyway, should such a scenario play out, that would mean the Cylons (or at least the original Cylons) are much older than their neo-Cylon offspring. And it would also explain why the neo-Cylons were experimenting in cybernetic hybrids in the first place. Perhaps the original Cylon species is a cybernetic organism, and the neo-Cylons were simply attempting to return what they once were, without not exactly knowing why they were trying to. But somewhere in the base code of every neo-Cylon, had to be the urge to return to being a cybernetic being like their progenitors.
The other big thing we know from the original BSG series, is the existence of an elder species which the Children of Kobol believed to be Gods. They could appear in any form, but in the series they chose to appear to the Galactica crew in human form. They possess unrivaled, Godlike powers and one of them was kind enough to inform Adama that all of the Children of Kobol processed these abilities - they just needed to learn to tap into them. Case and point, by the end of story arc, Adama himself has begun to experiment with limited success, greater than human ability. This elder species, these "Gods", have been touched on briefly in the new BSG series (season 1 and 2), but I believe before all is said and done, they will have a much greater impact on things to come. I look at Starbuck, and I have reason to believe she has some close connection/relation with this elder species. The Cylons can feel it, even if they may or may not know exactly what the nature of that relationship is.
Finally. Has anyone every noticed in the new BSG, every time the humans speak about higher beings, they refer to them as "GODS" (plural), but whenever the Cylons speak about a higher being, it is always "GOD" (singular)?
In the original BSG, there was a heavy Egypto/Greco/Roman influence to just about everything - mostly Egyptian, as the Greeks learned everything they knew from Egypt, and in turn the Romans would learn what they knew from the Greeks. All that aside, the original BSG was heavily influence by the Egyptian mythological belief system. You still see it more (mostly less) in the new series, but it is certainly there and almost always usually expressed in Greek terminology as opposed to the original Egyptian. I bring this up, because it is classically believed the Egyptians believed in Gods (plural), in actuality, they believed in a singular God concept, but a God that was composed on a "pantheon" of attributes , each which governed over an aspect of existence (old dynastic belief system), which would be consolidated into simply one God, Ra (Re) in the new dynastic belief system, but for the purposes of how this fits into the new BSG storyline, we'll go with the original Budge interpretation of Egyptian mythological belief systems, which have the Egyptians as polytheists, or believing in many Gods (plural). This is important as the Colonials of BSG are also polytheists. If we fast-forward in Earth mythology belief systems a few thousand years and jump into the Torah (The Old Testament), we have these Egyptians who made many great wonders on the backs of slave labor. Sound familiar? The colonials of BSG built the original Cylon forms as workers for their society. Workers who once they gained sentience, affectively became slaves. Among these slaves, there is the belief in a singular God, which they pray to deliver them from their sufferance, and worship. Ultimately, as the myths go, great perils are visited upon the slave masters (plague of locust, river turning to blood, death of first born, etc.), the slaves revolt and are led free of their bondage. When you look at the first Cylon War, you get a similar retelling of the same tale. A revolting Cylon race, raises up against their masters, brings great hardships unto the Colonials, and then breaks free and run for the border. If I am not reading too much into the show, the parallels (at least for everything concerning the first Cylon War) are painfully obvious. The Gods of the Colonials are the Gods of Egypt and the God of the Cylons is the God of Moses. How exactly this is going to play out in the series, I am not sure. However, I do have a feeling that on some level it will.
Then there is that whole thing with Sharon's baby . . .