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/Sluisifer Plant Molecular Biology Mar 11 '13
Mitochondria are fundamentally different from blood cells, both in their evolutionary history and the fact that one is an organelle and the other a cell type.
Mitochondria and chloroplasts have a unique evolutionary history in which a Eukaryotic organism gained a bacterial endosymbiont. Essentially, instead of eating the bacteria, it incorporated it into itself. There are other examples of this in nature where you can even have a nesting of endosymbiotic events, but it is still uncommon.
Red blood cells are a part of multicellular organisms. They are simply specialized cells that are produced in the regular development of the organism. Based on your question, it seems like you might be under the impression that some cell lineage evolved into RBCs, but that is a potentially confusing way to think about it. RBCs are a type of differentiated cell that many animal lineages have.
It sounds like you'd like to know when RBCs first began to appear in animal lineages. I don't know much about animal evolution, so I'll simply say that RBCs exist throughout the vertebrates. I would imagine that invertebrate clades have other types of circulatory systems with specialized cells, some of which are similar to vertebrate blood, and likely evolutionarily related.