all structures are well understood and simple. it's just, they all work together, and influence each other. and this, by today, is, even in case of a fly, out of our control.
thats why we can't understand a fly-brain. not because it's something strange, magic. the rules, with wich it works, we know, we can identify each component exactly, and what the part does. but we can NOT understand, and work with the whole brain at once. we can't get up to that complexity, it's much over our head, and computing-simulation-power.
it's similar to chess, understanding the rules is easy. winning against a master is near to impossible. you know the rules. you _should_ know how to win. why don't you? ... same reason we can't really use the knowledge we yet have. thinking on the whole isn't doable. but we can correctly identify each component, and what it does, on it's own.
proof? you know drugs yourself... there's tons of proof out there. medicine, sports, all the stuff, that has to do with our body. it's all just about how it reacts on different situations, influences.
we know the human brain about as good as you, and i can program c/c++. quite good, we know about all we need to, and can read all sort of code. the same way, we can read info in a brain today, easily. we can see the "brain-code" of your fly.
but even while we can read source-code, i'm not capable of reading the whole windows XP source, or the full linux source, and simply "go in there, and fix some problems".
and THATS nature. a human body is not billions of lines of code to read. it's sorta billion billions. while we can understand it's behaviour, we can not control that mass at once. not anytime soon.
and i still don't want robots to take our job on being "the dump-ass of the world"