How I look at Yeerk evolution is by noting that, between Gedds and Yeerks, the relationship is actually not a parasitic one. They have a true symbiotic relationship, beneficial for both species. The Yeerks get the Gedd's body, the Gedds get the benefit of the Yeerk's intelligence. Win-win.
I disagree. The Gedds lose control over themselves, and while they may not be intelligent by human/Yeerk/Andalite standards, they are still a sentient species.
If you recall in Book 6: The Capture, the Gedd was described to be fearful and bewildered by his imprisonment, while the Yeerk ruthlessly crushed and subdued the Gedd.
That doesn't sound beneficial for the Gedd. Doesn't sound like a win-win either. It is no symbiotic relationship, it is a parasitic one. True symbiosis would be the Iskroot.
Notice that I never said that the Gedds actually liked the arrangement. Only that it was beneficial from an evolutionary standpoint. Gedds are much less intelligent than Yeerks, therefore Gedds with a Yeerk in their heads are more likely to succeed and reproduce than Gedds that do not. They don't have to like it for it to be beneficial to their reproduction.
Evolution does a lot of things that animals don't like. As an example that's a little closer to home; humans' bodies store fat whenever we eat more than we need. Do we like it? No. Some of us spend our whole lives fighting that particular trait of our physiology. But is it evolutionarily beneficial to us? Yes.
All symbiosis really means, is something that is a mutual evolutionary benefit for both species. Do acacia trees like being protected by ants? Do ants like living in acacia trees? Neither species is even capable of 'liking' anything, yet that example is always cited as the classic example of symbiosis. Therefore, I still think Gedds and Yeerks count as symbiotes.
The Isk and the Yoort have a deeper symbiosis, of course, given that neither of them can even live without the other. Doesn't mean that Gedds and Yeerks are not symbiotic.
Before the Yeerks enslaved them, the Gedds seemed to be living just fine. There was no mention of unYeerked Gedds dying at a greater rate than those with Yeerks. By losing their freedom, that means the relationship between Yeerks and Gedds is NOT symbiotic and mutually beneficial. How can any sentient species think that losing their freedom is beneficial?
I'm not sure what the storing fat example has to do with the Yeerks evolution. Storing fat is beneficial to ourselves, but it does not involve taking over another species and causing them great harm. *shrug*
I also disagree with the trees/ants example, because those do not involve two sentient species. Trees and ants are not capable of making the choices that Yeerks and Gedds make.
My point about the storing fat example is simply that species do not always like what is evolutionarily beneficial to them. Evolution and symbiosis has nothing at all to do with personal freedoms or happiness.
And there was no mention of unYeerked Gedds dying at a greater rate, simply because there weren't enough free Gedds
left at that point for it to matter. I mean, the Yeerks pretty much had completely taken over their own planet by the time the Andalites got there, right?
Anyway, I think maybe I'm not being very clear, and that's why you're misunderstanding me. We seem to be operating under different definitions of the word 'beneficial.' I'm saying that it doesn't matter if the Gedds prefer, in their own minds, to be free or not to be free. If evolution selects for Gedd-controllers, then Gedds will evolve in that direction, whether they like it or not.
And, I would even go so far as to argue that some Gedds probably actually
did like to be infested. Otherwise, why would they seek out Yeerks in the first place? And if they didn't seek out Yeerks, then how could the Yeerks have found
them? And besides, evolution grants all species the
desire to do what is beneficial to their survival (in the Gedds' example, putting Yeerks in their ears), so it wouldn't be totally illogical to think that Gedds had perhaps evolved a deep-seated need for companionship, maybe even so strong that they couldn't function without another mind alongside theirs. The example that you cited in book #6 was one example, perhaps an aberrant Gedd, or maybe even a KASU (lord knows there are plenty of those). I don't think that it's a very good argument against symbiosis, though, even if it is true.
I'm going from the strict, scientific definition of symbiotes, which is merely two species that aid each others' evolutionary survival. And the Gedds and the Yeerks seem to fit that definition. You seem to have a different definition, though, and I think that's all we're really arguing about. I'm not saying, after all, that being a controller is in any way preferable, from a single individual's standpoint, over being free. But it's beneficial to the species, and to evolution, that's all that matters.