N.Drew, what you want isn't an answer or understanding. What you want is somebody with knowledge of biology to throw their arms up and say "Nobody knows! It's a bizarre mystery! It's completely illogical that things would evolve like they would given our current understanding of chemistry, physics, and biology! It's almost like there is some secret X factor that we can't pin down driving the whole thing.....strange....."
That isn't going to happen. You need to (A) stop anthropormophising biology. Asking how does something "know" to evolve a "finished product" is like asking how a ball "knows" to fall to it's "most desired position." A ball doesn't know to fall, and it doesn't desire to be anywhere. It's physics. Evolution doesn't know anything, and it's not working towards anything. It's chemistry and natural process. and (B) pay attention, and do it honestly. Your questions have been answered a hundred times in a hundred topics like these. If you can't see the answer, it's because you don't want to.
But in good faith I will give it another shot. There are no "unfinished" products in evolution. In order for a trait to be carried forward it either has to be so benign that it can hitch a ride by means of genetic drift, or it has to be beneficial. Which means any trait is already a "finished" product, no matter how flawed it might be. You don't see any "in development" traits because you don't know what they will be a million years from now. Your appendix is virtually useless, your eyes are a mess of engineering, your back isn't built for bipedal movement, the list goes on. But you don't see those as "unfinished" because they still work. In a million years human vertebrate may be vastly superior and better suited for upright bipedal movement, but right now that is not the case. If we were the finished product, then fuck us because our bodies are riddled with anatomical and biochemical problems. But we still work, at no point have we been an "unfinished product" and at no point will we be a "finished product." But all through our genetic legacy that has been the case. A light sensitive patch was not an "unfinished" eye, it was a useful aspect that helped an organism's reproductive success, and it just so happened that after a hundred million years or so, it was an eye. It's like asking for a transitional form, when everything is a transitional form, because there is no final or finished products. You're not going to find a lizard with only half a leg evolving into a whole leg, that doesn't even make sense. But you can find animals like the yellow bellied skink, that are gradually evolving to be more like snakes than lizards over a long period of time.
I don't know what you expect to see when you say you want to see something new evolving. I can point to monotremes that are mammals with venomous claws, duck bills, and lay eggs but you will probably just say "Well that's already a finished product, I want to see something NEW evolving." There are no finished products.
