It is important that these hematopoietic stem cells are able to undergo self-renewal because the human body needs billions of new hematopoietic cells each and every day. If the cells were not able to do this, humans would not be able to survive. There was an experiment that was done involving quail embryos on chicken yolk sacs that found complete opposite results of the experiment done by Sabin. In this experiment, it was found that yolk-sac progenitors only contributed on a small amount to hematopoiesis compared to the embryo. This experiment also showed that blood cells that were made by the yolk sac were not present when the bird hatched. Over time there have been experiments done that add to the confusion if the blood cells and red blood cells are related in the yolk sac and embryo.