The architecture of haematopoiesis — which is the process by which all blood cells originate — is essentially the same throughout the mammal world, report scientists in the Proceedings of the Royal Society. This is an unexpected result considering the thousands of mammals’ species with a myriad of habitats and lifestyles, as so well demonstrated when comparing the 30 mm flying bumblebee bat and the 30 meter-long aquatic blue whale both mammals.