Baby Fae body began generating isohaemagglutinins, but a suitable donor could not be found in time. Prior to the procedure, no infant heart transplant—even with human hearts—had been successfully performed due to a lack of infant human hearts. To address this issue, Bailey had become a pioneer in the research of cross-species heart transplants, which had included "more than 150 transplants in sheep, goats, and baboons". Multiple surgeons had previously experimented with baboon heart implants, leading some to speculate even that baboons could be farmed in the future for such purposes. When asked why he had picked a baboon over a primate
Baboon as a full species, but regard all the others as subspecies of "P. cynocephalus" and refer to them collectively as "savanna baboons". This may not be helpful: it is based on the argument that the hamadryas baboon is behaviorally and physically distinct from other baboon species, and that this reflects a separate evolutionary history. However, recent morphological and genetic studies of "Papio" show the hamadryas baboon to be more closely related to the northern baboon species (the Guinea and olive baboons) than to the southern species (the yellow and chacma baboons). In 2015 researchers found the oldest baboon fossil dating