BEIJING, July 2 -- For as long as medicine has tried to understand where human blood begins, the answer pointed inside the embryo. Three weeks into development, a process called gastrulation sets the body's basic architecture, and scientists believed it also triggered the first production of blood cells. A study published Thursday in the journal Nature, led by researchers at a Beijing institute, has moved that moment of origin to a different location and an earlier time.

The team, based at the Institute of Hematology and Blood Diseases Hospital at the Chinese Academy of Medical Sciences, worked alongside colleagues at Beijing Institute of Technology and the Chinese PLA General Hospital. They applied a technique called spatial transcripto...