Instinct - evolved or better answer?

On a number of threads I've seen people suggesting that instinctual practices (the building of certain kinds of nests, etc.) are too complex to have arisen out of natural selection.Then the other day I saw a little dog climb his back legs up a tree trunk in order to pee higher. It's not the first time I've seen this. It's always a small dog, though not always the same species.What occured to me was this - this behavior in this little dog could not have "evolved" since it's doubtful that the breed had existed long enough for such an occurance. Likewise, it's doubtful that the breeders were selecting for "high tree peeing".So why have I see so many little dogs do this?I suggest that it's as much an engineering problem as one of biology.Given a certain set of tools and a certain goal, chances are most participants are going to solve the problem the same way.A weaver bird doesn't need to evolve the "weaver nest" as though it were some blueprint stamped on the mind. It only needs to evolve the ability to weave reeds, the tendancy for curves, and the desire for a nest which is big enough to support it's weight. Given the simply programming for next building, the outcome is generally the same.Computer scientists have shown that with very little code they can make tiny robots which behave like insects. You don't need very many commands to create complex behavior.I'm not suggesting that no behavior / instinct is the result either directly or indirectly of evolution.What I am saying is that - if a little dog wants to pee higher than the other dogs, there's only one was he's going to do it.Thoughts?

Good question.I would suppose that this is where natural selection kicks in (futher blurring the engineering/evolution line). Obviously a bird who fails to build the nest isn't going to have a place to lay the eggs.I don't know how you'd measure this outside of the lab. We'd have to look for the nests that weren't built - hard to do.I'm not saying that evolution didn't play a role in these behaviors. I strongly believe that it did. What I'm suggesting is that, in the case of the weaver bird, all that's needed is - 1) A desire to build a nest, 2) the availability of grasses, 3) the ability to weave the grasses, 4) the birds morphological restrictions (ie the bird needs a nest X big, it's head tilts Y degrees left or right, etc). and 5) -speculative- a desire for a hanging nest as opposed to one that sits on the branches.I'd be interested to know if weaver birds hand raised from eggs will build weaver-type nests. I suspect they will.