The 'God-of-the-gaps' argument is thrown around very frequently where it doesn't fit.
No, theists reason that this aspect of human behavior requires God to be fully coherent, therefore God. Instead of just accepting that their behavior is not fully coherent.
Evolution designed us to value things but it didn't (can't) give us a reason to value those things. If you are going to value those things anyway, then I commend your complacency with the natural order of things, but you might still admit that your programming is incoherent if it simultaneously makes you want to do things for a reason and then makes you do things for no reason.
(If I sound angry it's because I'm furious, but not at you cithergoth. I'm angry with futility. I'll write up a post later describing what it's like to be 95% deconverted from belief in objective morality.)
If it's any consolation, you're likely to be a lot happier out the other side of your deconversion. When you're half converted, it feels like there is a True Morality, but it doesn't value anything. When you're out the other side you'll be a lot happier feeling that your values are enough.
Sometime ago Jonii wrote:
When I'm hungry I eat, but then I don't go on eating some more just to maximize a function. Eating isn't something I want a lot of. Likewise I don't want a ton of survival, just a bounded amount every day. Let's define a goal as big if you don't get full: every increment of effort/achievement is valuable, like paperclips to Clippy. Now do we have any big goals? Which ones?
Save the world. A great goal if you see a possible angle of attack, which I don't. The SIAI folks are more optimistic, but if they see a chink in the wall, they're yet to reveal it.
Help those who suffer. Morally upright but tricky to execute: James Shikwati, Dambisa Moyo and Kevin Myers show that even something as clear-cut as aid to Africa can be viewed as immoral. Still a good goal for anyone, though.
Procreate. This sounds fun! Fortunately, the same source that gave us this goal also gave us the means to achieve it, and intelligence is not among them. :-) And honestly, what sense in making 20 kids just to play the good-soldier routine for your genes? There's no unique "you gene" anyway, in several generations your descendants will be like everyone else's. Yeah, kids are fun, I'd like two or three.
Follow your muse. Music, comedy, videogame design, whatever. No limit to achievement! A lot of this is about signaling: would you still bother if all your successes were attributed to someone else's genetic talent? But even apart from the signaling angle, there's still the worrying feeling that entertainment is ultimately useless, like humanity-scale wireheading, not an actual goal for us to reach.
Accumulate power, money or experiences. What for? I never understood that.
Advance science. As Erik Naggum put it:
Don't know, but I'm pretty content with my life lately. Should I have a big goal at all? How about you?