The origin of blood cells can be traced back approximately 700 million years to when human ancestors were single-celled organisms. When these ancestors evolved into multicellular organisms (animals), macrophages emerged as the first blood cells. Over the course of subsequent evolution, various blood cells, such as mast cells, diversified.
KyotoU / Yosuke Nagahata
In a stunning, albeit unwitting, rebuttal of creationist claims, a team of researchers at Kyoto University is due to publish, on 29 May 2026, the results of their investigation into the evolutionary history of animal blood cells in Proceedings of the National Academy of Sciences of the United States of America (PNAS). The paper, entitled "Animals have expanded the evolutionary legacy of unicellular ancestors in blood cells", is unlikely to please those creationists who keep assuring their dupes that biomedical scientists are about to abandon 'Darwinism' and adopt creationism instead.
It will also disappoint those who insist there is no evidence for the evolution of complex multicellular organisms from single-celled ancestors — what they like to caricature as the 'microbes-to-man hypothesis', as though humans, preferably modern Americans, were the preordained end-point of the entire history of life. That, of course, is creationist teleology masquerading as biology: the assumption that evolution must have been aiming at us because Bronze Age religion says humans are the central purpose of creation.
What the Kyoto University team found was not a sudden, magical appearance of blood cells, but a deep evolutionary continuity. They developed a new method for comparing gene-expression profiles across different animal cell lineages and species, and included unicellular organisms in the comparison in order to trace the possible origin of blood cells back to our single-celled animal ancestors.
Among human blood-cell lineages, macrophages showed the closest resemblance to unicellular organisms. This is hardly surprising, since macrophages still behave in a remarkably cell-autonomous way: they move through tissues, detect targets, engulf bacteria, clear dead cells and remove unwanted material — behaviour strongly reminiscent of free-living phagocytic cells.
The team then traced the gene FOS, commonly expressed in blood cells across animal species, back to a single-celled ancestor that lived about 700 million years ago, around the time when the first animals were evolving. The implication is that the earliest animal blood cells did not appear from nowhere. They arose when early multicellular animals repurposed genetic programmes inherited from their unicellular predecessors.
From there, the researchers were able to reconstruct a family tree of blood-cell lineages spanning roughly 700 million years. Their analysis suggests that early blood cells were macrophage-like, that mast cells later branched from that macrophage lineage, and that prototypic T cells and red blood cells subsequently branched from mast cells. Prototypic B cells, meanwhile, appear to have branched from the macrophage lineage after mast cells had already diverged.
In other words, the blood and immune cells circulating in our bodies today are not isolated, specially-created structures with no history. They are modified descendants of ancient cellular systems, inherited, repurposed and diversified during the evolution of animals from unicellular ancestors.
So, far from supporting the creationist claim that there is no evidence for the evolution of complex life from single-celled ancestors, the evidence is literally circulating in our blood. It is also circulating in the blood and immune systems of other animals, carrying with it a molecular and cellular legacy hundreds of millions of years older than the creation myths of the Bronze Age.
And, as usual, the Theory of Evolution provides the only coherent explanation for the observable facts. The research does not point to separate acts of creation, nor to a sudden magical appearance of blood cells fully formed and without ancestry. It shows descent with modification, inherited genetic programmes, divergence of cell lineages, and the repurposing of ancient biological mechanisms — exactly the pattern evolutionary theory predicts, and exactly the pattern creationism cannot explain without special pleading.
