Clones assemble! The clonal complexity of blood during ontogeny and disease

•The clonal complexity of the hematopoietic system increases during early ontogeny but declines with age.•Novel non-invasive methods are shedding new light on our understanding of the clonal complexity of the blood throughout development•Clonal hematopoiesis is common in an aging hematopoietic system and associated with an increased risk of hematologic cancer and cardiovascular disease.•Bone marrow stress from cytotoxic chemotherapy or chronic...