Seeking to meet the demand, scientists explored other sources of supply, including different species. In 1984, for example, the fatally defective heart of a 12-day-old infant known as Baby Fae was replaced with the heart of a young baboon. Despite the use of cyclosporine, the baby rejected the heart and died 20 days after the operation. In 1992, a baboon's liver was used to treat a man dying of hepatitis. Similar operations followed soon after, using organs from baboons and pigs.

The long-term failure of these experiments, as with early transplants, comes back to the question of matching tissues. Now, however, instead of waiting for a close genetic match, scientists aim to produce one by genetic manipulation. In 1994, pigs were engineered with human genes so that their tissues produced human proteins that inhibit organ rejection. Hearts from the genetically altered pigs were subsequently transplanted into baboons (as models for humans). The primates survived only 19 hours after the operation, but they did much better than a control group of animals given regular pig hearts, which survived no longer than 40 minutes.

A different option for replacing some body parts is to use totally artificial structures, bypassing the need for donors of any kind. Thus, the heart's function of moving blood around the body can be carried out by a plastic and metal pump—surgery's greatest vindication of the materialist view of the body. This kind of development shifts attention from transplants to implants: fabricated body parts that can be manufactured. Included among implantable parts are such items as pacemakers, stainless steel hips, artificial lenses, and various other prosthetics. Such implant operations outnumber transplants in the United States by 100 to 1.