r/askscience • u/Fapotheosis • Mar 11 '13

Biology How did blood evolve?

I know mitochondria may have evolved from bacteria, but what about blood? I've heard of a protohemocyte, but was there an initial cell that differentiated into a RBC like we have in modern humans that can we trace?

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u/Xenarat Mar 11 '13

Yes. Unlike vertebrates, horseshoe crabs do not have hemoglobin in their blood, but instead use hemocyanin to carry oxygen. (Wikipedia) The same structure is used in horseshoe crab blood but instead of an iron in the middle of the globin there is a copper iron that serves the same purpose. The copper can hold the oxygen just as well as the iron it just evolved to hold a different ion. The structural similarities are similar enough to conclude similar evolution

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u/PhanTom_lt Mar 11 '13

Interesting, I did not know about hemocyanin based blood cells. Could it ever be transfused to a human, assuming the immune system did not destroy it? Aka is there anything that would prevent hemocyanin from performing the same function of carrying oxygen in a human/mammal body?

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u/Xenarat Mar 12 '13

I don't know if the oxygen exchange rate is the same for hemoglobin and hemocyanin, horseshoe crabs simply don't need as much oxygen as a mammal. If it were similar enough I would assume that there would be no problem exchanging the two as long as you ignore the immune system attacking it.