I don't know if this is original (a defining feature of this blog, besides utter neglect, is the ban on links and references - this being a content provider, not a content repeater), but I think it's odd that evolution has to bribe people to have sex. Reproduction is supposed to be the thing that evolution cares about more than anything else - sexual animals and plants should just have sex without thinking about it, or more importantly for this post, without feeling about it. So why does sex have to feel fun? Obviously the plan is to motivate people, or whatever other animals (or plants) have lustful qualia, into having sex voluntarily.
So lustful feelings only make sense if free will already exists (or co-evolved with the feelings). But isn't this pretty risky on evolution's part? If at some point in evolutionary history sex doesn't feel quite fun enough, a being with free will could just decide not to have it, and there goes the species. I guess this supports the co-evolution idea: if the being is already a stubborn free-willer before sex becomes fun, the species will die out, and there's no point in making sex fun if there's no free will involved. (Even nausea, another candidate for earliest qualia ever, provides a useful guide to behavior, if only to get you ready to set aside some alone time, maybe so you don't infect people - I dunno.)
Maybe that's why sex is so over-the-top fun (at least for many, maybe more males than females, since females can reproduce without having much fun at all). Lustful qualia is the result of an evolutionary arms race with free will, which maybe was becoming ever more aware how not-fun raising a baby can be. (Hm, but males don't help to raise the baby in all species - maybe in the species where they abandon the kids sex is less fun...?)
Lust doesn't seem to be a very sophisticated sort of qualia - the usual philosophical examples concern stuff like the "feeling of the color red" and such. So it should be relatively easy to trace the neurology, genetics, and evolutionary history of lustful feelings. This, in turn, might make it easier to trace the neurology, genetics, and evolutionary history of qualia more generally, and consciousness more generally than that.
There's one mystery solved. Don't say this blog doesn't give the public what it wants.