Are zookeepers playing God?

There are lions, tigers, and bears -- but when it comes to the zoo, people rarely think about the birds and the bees.

This week on 60 Minutes, correspondent Lesley Stahl does just that, reporting on the methods zoos use to manage their animal populations. Gone are the days of taking animals out of the wild; most zoos rarely do that anymore. Instead, zoos today engineer animal reproduction in a decidedly unnatural -- but very of-the-moment -- way: using a computerized pairing program. Think of it as Match.com for animals.

The point of such careful coupling -- which can send one animal on a trip hundreds of miles away to mate with another -- is to maintain genetic diversity. And in a small, closed population like a zoo, that variety is vital for the species' survival. Zookeepers effectively decide which animals get to mate and which animals they mate with.

In some zoos, they also determine which animals get to live.

In some cases, an animal in captivity has a genetic profile that's well-represented in the global zoo population, so a zookeeper will prevent that animal from mating. In the U.S., zookeepers often put these animals on birth control. 60 Minutes cameras filmed a gorilla, a monkey, an aardvark, and a rock hyrax all receiving some type of contraception to prevent them from passing on genes that are too common in captivity.

But some European zoos have a different philosophy. They believe animals should be able to breed and have babies, just as they would in the wild. The problem then arises when it comes to finding homes for those offspring.

In Copenhagen, zookeepers have had to address this issue with giraffes. A young female born in the Copenhagen Zoo cannot stay there because once she matures, her father will mate with her, giving rise to inbreeding. It's not hard to find another home for a female giraffe at another zoo, however, because giraffes live in harem groups of multiple females and one male.

For young male giraffes, it's another story. At the Copenhagen Zoo, a male giraffe named Marius couldn't stay in his family because once he matured, he started challenging his father, as adolescent giraffes do -- and zoo staff feared his father would kill him. Other European zoos already had male giraffes, so he couldn't be rehomed, and releasing him into the wild would likely lead to other giraffes killing him. So the Copenhagen Zoo ended his life, dissected his body before a public audience, and fed his remains to lions.

The zoo received international criticism as a result. But Bengt Holst, the director of research and conservation at the Copenhagen Zoo, told Stahl the decision was necessary -- and natural.

"Animals, they die," Holst tells Stahl. "They are born, and they die. In the wild, they die. Maybe they die on the same day they are born because they are eaten by a lion or by a hyena. That's what happens. And also, we have to make sure that the right animals are always in the population so the population is healthy."

Back in the U.S., Ron Kagan, the executive director of the Detroit Zoo, disagrees. He adamantly opposes culling healthy animals in service of genetic diversity and tells Stahl that ending the life of a healthy animal is killing -- not euthanasia.

Stahl acknowledges that her story raises an ethical debate. "We're playing God. We are," she says. "But on the other hand, we're trying to save these animals who are being depleted so quickly off the planet."

Stahl says it's important to remember the broader context: Fewer and fewer animals can survive in the wild, so zoos are beholden to keep the animal populations in captivity alive and well.

"There will be a day, I think, when if you want to see a giraffe, you're going to have to go to a zoo," she says. "And so we better be rooting for them to continue their conservation work."

Video of Marius courtesy of DR -- Danish Broadcasting Corp., TV 2 Lorry Denmark and the Copenhagen Zoo

The video above was produced by Lisa Orlando and Ann Silvio, and edited by Lisa Orlando.