How Did RBCs Evolve?

February 3, 2012 at 9:20 am

By Billie Rubin, Hemoglobin’s Catabolic Cousin, reporting from the labs of Stanford Blood Center

Ill-conceived blood transfusions go back to the 1600’s (disastrous transfusions of lamb’s blood into humans), and the discovery of the ABO system goes back to the early 1900s. But just how old is blood itself? A picture from the Smithsonian in 2009 showed a red blood cell (RBC) in the soft tissue of a Tyrannosaurus Rex bone from 68 million years ago.

But blood cells go back, really far back. The first ones to evolve may have performed a mixed function of what white blood cells and red blood cells do now. Here’s what the U.S. National Library of Medicine, National Institute of Health has to say: “The most primitive blood cell may have been a protohemocyte which was first involved in phagocytosis and nutrition. When metazoans (sponges) appeared [hundreds of millions of years ago], their “blood” cells, the archeocytes, were phagocytic. [Later] a progressive differentiation of several leukocytic types occurred. Differentiated cells appeared that distributed food and oxygen, thus erythrocytes evolved in certain marine or polychaete annelids [worms].”

In other words, the earliest ancestor of blood cells may have been one type of cell that provided both immunity and energy to the organism. Later, in what may have been sponges or marine worms, this “proto” blood cell evolved into several types of cells involved with immunity (WBCs) and other blood cells that distributed nutrients (plasma) and oxygen (RBCs).