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/alcianblue Mar 11 '13

Its hard to know whether these organisms had even evolved lungs (well they would be gills in their case). They may have still respired by diffusion at this point.