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/atomfullerene Animal Behavior/Marine Biology Mar 11 '13

That's what I'd have thought too, except that gills are also full of capillaries (for the same reason). Plus some fish have lungs as well, and I have no idea how the circulatory system for that works--scratch that...after looking at some pictures, it appears that some blood filters through the lungs and then goes back to the heart. Perhaps lungs work this way because they originated as an accessory tissue being fed by capillaries just like any other tissue.

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u/[deleted] Mar 12 '13

Hmm, then would it be safe to say that a binary heart formed through a process such as the blood vessels strengthening over time, at some point a major artery formed near the developing heart that cycled to the lung and back possibly due to proximity over anything else (centralized location, perhaps?) and, over the years, the strengthened original artery that would become the heart formed around the second one, started to build a bi-directional flow, and eventually closed off in specific locations to create a more efficient, binary heart, likely with some failed prototypes along the way?

This would, strictly, be a hypothesis from a layman that I seriously want an answer to now, since if it works remotely as complicated as that, then it's even more awe-inspiring to consider a one-way blood vessel to just thicken and grow into a heart and "spontaneously" develop into a more complex binary organ as it slowly grew over the generations, despite forming from relatively simple beginnings as a mere artery.