When surgeons in Pittsburgh transplanted a baboon liver into a 35-year-old dying man, animal rights activists protested, arguing that a baboon's life should be valued as something more than a spare-parts factory for humans. That line of reasoning fizzled somewhat when a man suffering from liver disease angrily confronted the demonstrators.
Any time the welfare of animals clashes with the lives of humans, most people would agree that humans should take precedence. So it does not bode well for the animal rights movement that these clashes are bound to increase.
Spare parts aside, in much of the world animals are increasingly in competition with humans for land and food. As the world's population grows -- and it is currently expanding at a head-spinning pace -- people are increasingly edging out elephants and hippopotamuses, snail darters and spotted owls.
A vivid example comes from Zimbabwe, now suffering from a deadly drought. Compared to neighboring Kenya, Zimbabwe has been relatively successful at protecting its wildlife from poachers. Now, however, the government is sanctioning large kills of elephants and other animals, and much of the meat is being given to families who would otherwise go hungry.
Even wildlife experts agree that in this case killing the animals and feeding humans is a better solution than letting both starve. Zim- babwe's 2,000-square-mile Gonarezhou National Park is already overpopulated with wildlife, and the goodwill the plan will create among hungry peasants may reduce illegal wildlife kills in the future.
The story helps to dramatize a situation that too often gets lost in the bio-babble of environmental talk: Population stability is a critical component in protecting the Earth's environment and in helping to preserve its diversity of plant and animal life.
Remember Rio, last month's environmental story? For all the talk of biodiversity and global warming, we heard little or nothing about the major role that sheer numbers of people will play in the struggle to keep the planet livable.
So it's worth mentioning that yesterday, designated by the United Nations Population Fund as World Population Day, the Earth's population stood at about 5.5 billion people. If current trends continue, demographic experts predict that world population could easily reach or exceed 19 billion people by the year 2100.
Much of that growth will occur in developing countries such as Zimbabwe and Kenya where drought, economic dislocation and political instability already complicate the job of feeding, sheltering and educating people.
Pity the poor elephants. With 19 billion humans on the Earth, a 2,000-square-mile wildlife park will probably be an unaffordable luxury for all but the richest of nations.
Unfortunately, population is one of those unglamorous issues, riddled with statistical predictions of dangers down the road, that is easy to shove aside as tomorrow's problem. And tomorrow never comes -- or does it?
True, some of the doomsday warnings about population growth may have been a bit off in their timing; after all, human civilization hasn't yet collapsed. There is still time to avert disaster. But the notion propounded by some economists that population growth merely represents more human capital that can produce more prosperity will sound increasingly ludicrous in the years to come. Sooner or later, population pressures could easily lead to disaster.
It won't happen all at once -- just as all those billions more people won't arrive all at once. But year by year, the toll humans take on the Earth will become more apparent in exhausted farmland, disappearing forests, fewer songbirds and frogs, more days of smoggy air, dirtier (and more expensive) water, more refugees from environmental disasters and from political instability caused part by population pressures -- as well as government-sanctioned programs to shoot elephants and impalas.
There will also be other, less apparent consequences of human dominance. At least one biologist predicts that viruses similar to the one that causes AIDS will crop up around the planet to plague us. After all, when any species becomes too plentiful it presents a tempting target for new predators, even microscopic ones.
Review the population projections and you will find plenty to worry about. Today or tomorrow, the crunch will surely come. When it does, debates about the rights and wrongs of using animals as spare parts for human bodies will, in retrospect, seem like luxurious child's play.
Sara Engram is editorial-page director of The Evening Sun.