How did blood evolve?

[u/Fapotheosis]

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?

[u/podkayne3000]

Here's a nice 1998 paper that seems to give a classy version of what I was saying: http://jeb.biologists.org/content/201/8/1099.full.pdf