Starting in the 1960s, doctors attempted transplants of kidneys, hearts, and livers from baboons and chimpanzees—humans’ closest genetic relatives—into people. But the organs failed within weeks, if not days, due to rejection or infection. These efforts were largely abandoned after “Baby Fae,” an infant with a fatal heart condition, died within a month of receiving a baboon heart transplant in 1984. (Her immune system rejected the heart.)
By the 1990s, researchers turned their attention to pigs. Their organs are more similar in size to human ones and take only months to grow to a size suitable for donation. Unlike primates, there’s less concern about them passing on HIV-like viruses to patients (though pigs harbor different kinds of viruses). And scientists thought pig donors would be more accepted by the public, since they are already raised for agriculture.
But biological differences between pigs and humans make transplantation much more challenging. So