Certain marine animals (like the ancient horseshoe crab and the octopus) have blood which is green-instead of hemoglobin (the iron compound that carries the oxygen in our blood), they use a copper compound.
My question: why would evolution cause such different chemicals to be used? I understand that the copper compound is not as efficient as iron on carrying oxygen…and that iron is a more common metal than copper-so why this evolutionary quirk?
Other than this, is the physiologyof copper-based blood pretty much the same as iron based hemoglobin?
Horseshoe crabs have been unchanged for millions of years, and I know they have blue blood.
Evolution: there is more than one way to accomplish many things, and evolution bears this out time and time again. The real question is why you would only worry about blood, because there as so many things that are different, yet accomplish the same things…especially in animals that evolved along different paths.
Evolution doesn’t have a plan it works buy random selection, based upon what happens to be available.
Evolution is hit-and-miss; it works using the materials at hand, which may not necessarily be the optimal ones.
You might as well ask why mammals like us have a respiratory so much less efficient than that of birds, which use their air-sac system to pass air through the lungs in just one direction, rather than the wasteful in-and-out system we have.