So why do we find structures with similar or even identical function yet vastly different construction in different animal species?
What I see as a coder is this vastly different construction is using the same building blocks (cells) and new combinations of similar rules (or Code in my world). We just don’t have access to the source code or good documentation. Without the code, all we have is useless parts. If you ever experience the joy in reverse engineering an existing complex system without any access to the source code you would better understand this. So much of any system seems simple from the outside. Often this is only what our less techie managers see. Then when it comes to parallel testing the old one and the new one you start seeing how much you missed and much of this can only be seen when you start pumping in years worth of data and calculations. Welcome to my world.Google Chaos theory and weather models , or the butterfly effect if you want to delve deeper.
but often superior than many of the other types.
Superior in what sense? If all creatures had this superior vision what would happen to those creatures that survival depends on the poor seeing prey? Things are designed to fit into a whole that neither of us will ever be able to get our mind around. We are talking about cause and effect in large complex systems.
broken vitamin C synthesis in primates.
You can NOT say with certainty that this serves no usefull purpose. Design always involves trade offs, think armor v. speed. We can say with certainty that we do not fully understand this yet. We can even say at this point with our current knowledge it looks like poor design. How much knowledge does Science lose when we think we are done in knowing anything? You see “broken”, I see perfection not yet realized. Which Scientist is better, the one that stops digging out answers or the one who keeps on digging deeper?
I run into this when I have to fix other's code that is poorly documented. I remove the line that I think is useless only to get burned may months later when the right combination of complexity/logic ends up needing this line of code that I arrogantly removed. Things like this keep me humble. Now take into account that none of the code that I have ever worked with even comes close to the complexity of systems in living things such as eyes.