优乐娱乐参考文本（文本与音频不全一致，敬请谅解）：They're called "transplant tourists." In need of an organ transplant but lacking a donor, they travel to countries where human organs are available for purchase on the black market. The organs they buy are harvested from the poorest of the poor, those who are most desperate for money. Often, after the organs are taken, the promised payments are never made.
Monir Moniruzzaman is an assistant professor in the Department of Anthropology at Michigan State University. He's studied the sales of organs by people trapped in extreme poverty and was invited to the Vatican to participate in a summit on organ trafficking.
Moniruzzaman told us the problem started in 1971 with the development of the drug cyclosporine, which prevents organ rejection. Since then, in the United States and other countries, the number of organs legally donated has fallen far short of the increased demand.
"There is a big waiting list, often it is five years or so," Moniruzzaman said. "So to bypass this waiting list, some of the recipients, they are going overseas and they are having the transplantation done in those countries. So that’s why the black market is flourishing, for the last three decades or so."
Advances in medical science have only worsened the issue, as more organs have become transplantable. Originally the black market consisted only of kidneys. More recently, liver lobes have become available. Moniruzzaman described one case in which a poor woman wanted to sell one of her corneas.
While selling organs is illegal in nearly every country on Earth, limiting the black market can be difficult, especially when most buyers come from abroad.
Moniruzzaman explained one way of dealing with the problem that doesn’t require any legal intervention: simply increase the number of legal donors. Spain, for instance, has a "presumed consent" system where those who don’t want to be donors must opt out. That leads to higher levels of organ donation than in countries like the U.S., which has an opt-in system.
Misconceptions and fears about organ donation also limit the number of donors.
During his visit to the Vatican, Moniruzzaman hopes to enlist the help of the Pope to increase the level of donation in the U.S. and around the world.
"If Pope Francis calls for organ donation, more and more people will step forward, which will reduce the black market for organ trafficking," he said.
Listen to our full interview with Monir Moniruzzaman, assistant professor in the Department of Anthropology at Michigan State University, above.