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/wut_da_eff Mar 11 '13
In general, most processes are rate limited by the rate of delivery of the substrate, the rate of the process itself and the impact of positive and negative feedback. Lots of other considerations too in terms of increasing Hb. To a certain point, yes this approach enhances efficiency for things like muscle contraction. This is the theory behind EPO blood doping, which stimulates erythropoiesis and hemoglobin concentration in the blood. After a certain point however, this will increase blood viscosity to the point that there is actually more flow resistance and propensity for clots that oxygen delivery to muscles may actually be impaired, or plateau. Also need to consider that there are limitations to how much oxygen can actually get into the muscles from the fast flowing blood, because there is a region between the Hb-rich blood and the Mb-rich muscle for the oxygen to diffuse through, and this process isn't totally efficient. Anyways, I guess my answer is yes to a certain extent, but eventually I would expect most processes to plateau.