What is the origin of the normal ranges of blood cell counts? An evolutionary perspective

The normal values of the complete blood count are part of the foundational medical knowledge that is seldom questioned due to their well-established nature. These normal values are critical for optimal physiological function while minimizing the harmful consequences of an excessive number of blood cells. Thus, they represent an evolutionary trade-off likely shaped by natural selection if they significantly influence individual fitness and exhibit heritability.

On the basis of the analysis of normal blood count values of 94 mammalian species, we discovered that certain parameters are strongly associated with diet, habitat, and lifespan.

Carnivorous mammals had higher hemoglobin levels than vegetarians, and aquatic mammals displayed red blood cell parameters probably selected to enhance for the diving capacities. Body weight influenced platelet counts and innate immune cells, with lighter animals having higher platelet counts and larger animals showing elevated monocytes and neutrophils.

By treating the history of life as an experiment, we have discerned some evolutionary constraints likely contributing to the selection for optimal trade-offs in blood cell count.