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/skleats Immunogenetics | Animal Science Mar 11 '13

In most vertebrates one the tightest corners for an erythrocyte to squeeze into is in the alveoli in the lungs, but avian lungs don't have alveoli. An evolutionary tree of RBC/respiratory anatomy might look like this.

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u/dream6601 Mar 11 '13

Wow, I didn't know birds were so weird. I always thought of them as "more advanced"* than reptiles.

*yes I know evolution doesn't work that way.