Goa'uld origin theory (6.22 spoilers)

[Sindri]

Spoilers for Full Circle
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The Goa'uld have some unique characteristics that are not normally expected in nature. Each parasite can assume control and access the memories of an alien species while providing physical augmentations and accelerating regeneration. It is also suggested in The First Ones that there was some interference to first get naquadah in their blood.
My own suggestion of how the Goa'uld came into existence is the Ancients genetically engineered them. As the Plague was spreading across the galaxy the Ancients could have attempted to create a race to transfer their consciousness into that would be immune to the Plague. Humans were vulnerable to the disease and their neural physiology wasn't sufficiently advanced. Instead the Ancients found an immune river snake and modified it to accept their consciousness. They also bioengineered this species to be capable of assuming control of a human host and boosting the host's immune system to improve Plague resistance. The Ancient controlled parasite would frequently change hosts as each one succumbed to the Plague. This would have allowed the Ancients to exist in a similar form to their original state without having the deterioration problems blighting the Asgard.

 

[PTeppic]

That would probably be reasonably consistent with most of what we know... except that they wouldn't have needed to let the remaining symbiotes run riot around the galaxy.

It also seems to clash with "The First Ones" comments and examples that the natural (un-naquadah'd) symbiotes are also still capable of mind control. There are dozens of examples of symbiotic creatures and relationships in Earth's nature, just not quite as blatant as symbiote and host in this particular manner. Although the Ancient's event in 6.22 are un-dated, the prehistoric symbiote fossils may predate it.

 

[Sindri]

Allowing the modified symbiotes free reign over the galaxy could have been the result of an accident or oversight by the Ancients. Or it could be due to their apathy towards events in this galaxy demonstrated in Full Circle.
Indeed, there are symbiotic relationships on Earth involving the parasite influencing the host. Although the parasite having absolute control over the host's movement and sufficient mastery over its neurology to access specific memories would be in a completely different league to anything on Earth. I'm convinced this level of control is impossible without intelligent design.
The naquadah-less symbiotes in The First Ones could have been the engineered symbiotes or from some pre-final stage in the modification process. Naquadah addition could have been at a very advanced stage or was a modification made by the Goa'uld themselves and not part of the Ancients' plans. The prehistoric fossils in The First Ones were not parasitical.
This theory would also justify why the Goa'uld prefer humans as hosts because this is the species they're engineered for, making control easier. It may also reduce the discontinuity between the motion picture by having a race dying and attempting to transfer their consciousness into another species.
Although one of the problems I can't satisfactorily explain with this theory is why the Tau'ri were not wiped out by the Plague. Earth could have had all traffic to it strictly controlled and subjects removed remotely.

 

[PTeppic]

Some of the latter stuff above seems to disagree with what we know... humans were only lately (relatively) taken as hosts by the Goa'uld: Unas and other, nastier, hosts were used before that. Humans were used because they healed really easily in sarcophaguses. Which is odd, given how resilient Unas are... surely they would be better? Maybe they don't heal well in the sarc., although being naturally resilient. We also don't know that the prehistoric symbiotes weren't parasitic: the Unas have developed sufficiently to know of the problem and avoid being "impregnated" by the current aboriginal symbiotes.

 

[Sindri]

I would suggest the engineered symbiotes escaped or were abandoned on the planet in The First Ones then took the indigenous Unas as hosts in the absence of humans. Once the Goa'uld got access to Earth they could have begun using human hosts.
An Unas is certainly more imposing and resilient than a human. My suggestion is humans are a subspecies of the Ancients so they designed the Goa'uld for human hosts. The Ancients could then exist with a similar physical appearance and form to their natural state. With this the Goa'uld would prefer human hosts because they were designed for humans making control easier and more effective. If the Goa'uld evolved taking Unas as hosts they would probably be biased towards continuing using Unas.
Evolution 7.11 spoilers:

Spoiler

It is stated the sarcophagus was developed from Ancient technology. As humans are very similar to the Ancients it makes sense the sarcophagus is more effective at healing humans.

The fossilised creature Jackson and Rothman found in The First Ones was predatory instead of parasitical. It can't be inferred when the Unas started wearing necklace defences. There is no evidence the Goa'uld evolved to become parasites.

 

[PTeppic]

Not sure I agree yet, mostly because it seems so different, but its certainly very convincing and well argued. All the bits seem to fit together with everything we know [though I've only just got up to 6.22]... wonder if this is where the series is going by the end of s7?

 

[PTeppic]

Just thought of a problem with the theory - known Ancient technology specifically doesn't work with Goa'uld carrying people - e.g. the Teaching device in "5th Race"

 

[Sindri]

Most of the examples of technology that disregards symbiotes are not Ancient. The only cases seen other than The Fifth Race are the aliens from Crystal Skull and Asgard technology. There is also an alternative explanation offered for why the Ancient device accepted O'Neill but not Teal'c in season 7.
7.03 Fragile Balance spoilers:

Spoiler

O'Neill is stated as being a more advanced form of human than anyone in the previous generation. It is asserted that this was why the download worked on him. Therefore the Ancient repository didn't necessarily discriminate against the Goa'uld.

 

[PTeppic]

I'm coming more and more onto the (at least plausibility) of this theory - to answer my own query above, it could be that the Ancients did it deliberately, to not harm the symbiotes, since there would be two minds present at once...