Right, and stuff like this very easy to misconstrue. Think of all the ways that life survives here on Earth. Looking at an individual case almost always makes it seem like there is intent in the design. Scaling back your perspective though, it’s more clear that nothing makes intuitive sense. It’s like biology threw everything it had at the wall, saw what stuck, and kept it going until it didn’t stick anymore. Most adaptations are odd ball solutions when looking at the big picture, like a virus surviving by infecting rats -> making the rats fear less -> rat eaten by a cat -> virus reproduces in cat tummy -> cat poops out baby virus -> rat eats poop -> rinse and repeat.

Fun fact: had we evolved to use copper instead of iron in our blood… our blood would be green. Why did we evolve to use iron? The reason Iron is used is because it holds a very specific place on the periodic table which makes it stable enough to be held by your cells, common enough to be ingested from organisms in your surroundings, and reactive enough that oxygen will readily latch on to it.

There are copper-based oxygen-carrying pigments, such as haemocyanin, found in some crustaceans & mollusks. They are only about a quarter as effective in carrying oxygen, molecule for molecule, than haemoglobin, because they do not have the steric interaction of the haemoglobin subunits that confer a sigmoid saturation curve upon haemoglobin.

So it’s likely we adapted to using iron to support our need for utilizing more oxygen within our blood. More oxygen supports a huge array of other things.

We also cook our food to break it down more and extract more calories from it. This supports, among other things, our “big brains”. Did you know cows have four stomachs to support digestion of raw grass?

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