The following script is from "Back to the Wild" which aired on March 15, 2015, and was rebroadcast on August 9, 2015. Lesley Stahl is the correspondent. Shachar Bar-On and Alexandra Poolos, producers.
More Americans go to zoos every year than to professional baseball, football, hockey and basketball games -- combined. We get to encounter the dangers of the wild from the safety of suburbia. But increasingly zoos see their mission as not just displaying animals, but also saving endangered species. And that raises an interesting question: can endangered animals born and bred in captivity be released into the wild? As we first reported in March, a conservation group called the Aspinall Foundation is trying to find out. It's run by Damian Aspinall, a multimillionaire who owns a chain of casinos in England but his biggest gamble involves his animals.
They say that the English can be eccentric, but Damian Aspinall takes the cake. This 54-year-old likes to play tug-of-war with tigers and pet black rhinos. But gorillas are his best buddies -- and wrestling with them is his favorite pastime.
Damian Aspinall: They're part of my family, and I'm part of their family. They see me as an intricate part of their lives. And when I look after these animals, they're my equal.
Damian Aspinall: Now the tricky thing is getting out! [Gorilla clobbers him.]I'm not allowed to leave.
Damian gets to do this because he oversees a 500-acre wildlife park that looks like the Serengeti, but is in Kent, England, surrounding Damian's country estates. The zoo was started by his wealthy and no-less-eccentric father, who liked to take a dip in the pool with the tigers and let the gorillas roam about the grounds.
"If I could extinguish all zoos over the next 30 years, including my own, I would. I wouldn't hesitate."
Lesley Stahl: When you were a little boy were the gorillas your playmates?
Damian Aspinall: Yeah without question. The problem being of course that you never had any human friends 'cause no parents would ever let you have a play date.
When Damian took over the zoo, he set out to save the species: over 130 critically endangered western lowland gorillas have been bred here, more than any other zoo on Earth. Also 30 near extinct black rhinos, 180 tigers, and 140 rare clouded-leopards...but not to keep them. It wasn't long before Damian decided that zoos are immoral; they're jails that lock up the innocent for life. So his goal now is to set all the animals that were born here free.
Damian Aspinall: If I could extinguish all zoos over the next 30 years, including my own, I would. I wouldn't hesitate.
Lesley Stahl: And you don't think, as many do, that the zoo animal is an ambassador and that they educate the public who then in turn become more interested in conservation.
Damian Aspinall: Please show me the statistical evidence that zoos educate. And that education that they claim they're doing has helped animals in the wild. There is no evidence because it's a lie.
Lesley Stahl: But if you go to a zoo you should see the faces of children when they actually see an animal.
Damian Aspinall: But that's so wrong.
Lesley Stahl: But it's-- it--
Damian Aspinall: They should-- their face should be one of disgust. That's what's so wrong. We've culturalized them that, "Oh, those animals are here for our pleasure." They're not. We don't have the right as a species to take animals to pleasure our children. That disgusts me. These poor animals.
So this zookeeper who hates zoos announced that he was going to send an entire family of zoo-born gorillas to Africa: a silverback named Djala, his five wives and four infants: a project no other zoo would even consider.
Lesley Stahl: Why isn't anybody else doing it?
Damian Aspinall: Because they don't believe in it. You gotta understand, we're considered mavericks. You know -
Lesley Stahl: You're actually considered a little nutty.
Damian Aspinall: Yeah. But that's such a good thing. 'Cause it's only the nutty people who ever get anything done in this world.
But these giants are actually very fragile, they get stressed and even depressed by change; finding it hard to adapt to new environments. Especially the adults.
Lesley Stahl: You know, people think "Well, we're going to send them home to Africa." This is home. They were born here. Why would they wanna go back if they're living a cushy-
Damian Aspinall: Why wouldn't they wanna go back?
Lesley Stahl: Well, 'cause it's cushy here.
Damian Aspinall: But-- so you decide that?
Lesley Stahl: But you're deciding to send them back.
Damian Aspinall: Because that's where they belong. I'm not really deciding anything. They're for 50,000 years have evolved in this forest. That's surely where they belong, not after 12 years living in a zoo.
Lesley Stahl: But isn't it dangerous for the animals to release them into the wild if they've been raised in a place like this where they're pampered and they're fed? How can they survive in the wild?
Damian Aspinall: Man always underestimates the intelligence of wild animals. You have to help them on their way. But if you leave them be, they'll pick it up immediately.
To help them on their way, Damian created gorilla school in his mansion's backyard, where he himself taught these English-born infants survival basics like how to climb a tree and avoid poison berries. Still, sending the family of 10 gorillas to Africa was a massive undertaking: they had to be sedated and couriered - you couldn't make this up - by DHL!
Lesley Stahl: Was that hard for you? You're basically sending your family away.
Damian Aspinall: Honestly, no. I'm so proud that they're going where they belong. But if I didn't do it, I would not live easy within myself.
The gorillas were flown to Gabon and taken by raft to this dense forest -- about a million acres that he bought and turned into a national park to protect animals like the western lowland gorillas whose numbers keep dwindling due to habitat destruction and poaching.
Lesley Stahl: I'm wondering why the poachers even want gorillas. They don't have horns. They don't have ivory.
Damian Aspinall: Bush meat. They'll eat the gorillas.
Lesley Stahl: They are poaching them to--
Damian Aspinall: They'll cut the hands off--
Lesley Stahl: --to eat them?
Damian Aspinall: --and sell them as ashtrays. The babies are taken for pet trade.
To keep them safe, the gorillas were taken at first to an island to acclimate. Damian's staff continued to feed them and give them medicines like malaria pills. This wasn't his first time sending gorillas here. He had already sent 12 from his zoo, but they were all babies who hadn't adapted yet to the zoo. He's taken many trips to see how they're doing: he says most of them have survived, and multiplied. But on one visit -- that he videotaped -- he was concerned about one of them, Kwibi, who hadn't been seen in a long time.
Damian Aspinall: And I went up the river and called for him. He obviously heard my call and he came down to the edge of the river. And I jumped out of the boat and I went to see him, and he greeted me with a fantastic gurgle-- love gurgle. We sat there together, and he was so sweet, and he introduced me to all his wives. And then when I wanted to leave, he wouldn't let me leave. He clung onto me very tightly. He wanted me to stay. But you know, I know the best thing for him was for me not to stay, and he's wild, and let him be wild.
[Damian to Kwibi: I'll come see you tomorrow, OK? All right, I'll come see you tomorrow.]
Looks idyllic, but conservationists we spoke to were critical of Damian, some calling his work a vanity project.
Tara Stoinski: Maybe it makes him feel good. He has a relationship with these animals. And he wants to do well for them. And he thinks that taking them back to Africa will be doing that. But it's not conservation.
Tara Stoinski is president of the Dian Fossey Gorilla Fund, run out of Zoo Atlanta, home to the largest collection of gorillas in North America. She says returning a handful of zoo animals can't begin to counter the vast numbers that are lost every year, so Damian's money would be better spent saving gorillas already in the wild.
Tara Stoinski: We need all hands on deck right now to be conserving wild populations. We need funds to be going into saving these wild places so that the animals that are living there currently can continue to survive.
Lesley Stahl: You know, there's just something kind of, I think, in us, intuitively in us, that we want to see these animals roaming free.
Tara Stoinski: I think that humans have a very romantic notion of what the wild is like, and the wild is not a place where it is safe, and animals get to roam free and make choices. They have to find food, they have to avoid predators, they have to find mates. And then you add on top of that all of the challenges that humans are imposing, whether it be hunting, habitat loss, disease. I think the challenges that these wild populations are facing are huge.
One year after the silverback from Kent, Djala, and his family were sent to Gabon - we went with Damian to see how they were coping.
We snaked down the Mpassa River, but there was no sign of Djala thru the dense vegetation. Then, a glimpse of eyes and limbs through the trees. As our boat approached, the females and infants came slowly into the clearing.
Damian Aspinall: They're so calm, it's such a beautiful thing to see! I mean, how happy do they look?
But when Djala came forward, he didn't look all that happy.
Damian Aspinall: He knows I'm here now. He's protecting the females. He's looking at me.
But Damian was ecstatic - as they settled on the grass in front of us.
Damian Aspinall: One two... three... four... five... six... seven... eight... nine --
... A full house.
Lesley Stahl: Did you give the baby a name?
Damian Aspinall: That's Akou.
Lesley Stahl: Akou?
Damian began tossing them coconuts, sugar cane and bananas.
Damian Aspinall: That's Tamki. She's calling for some: hey!
Lesley Stahl: She keeps wanting more!
Damian Aspinall: "You're so silly"... She's smart though because she get more than anyone else.
Lesley Stahl: Do you think that you have brought them home?
Damian Aspinall: Without any question. Yeah.
But they weren't totally free yet. Damian's idea was to complete this bridge only when he felt they could fend for themselves.
Damian Aspinall: And just over the other side of that bridge is the true wilderness.
Lesley Stahl: They don't swim.
Damian Aspinall: No. So, here, they're protected 'cause they're on an island. But once they cross the bridge, they'll come across elephants and leopards and other gorillas. Djala's gonna be, you know, defending his females. He might lose some of his females. It could become very stressful--
Lesley Stahl: You mean other males--
Damian Aspinall: Other males, yeah.
Lesley Stahl: --who are there wild.
Damian Aspinall: Yes, wild, who-- want his females
Lesley Stahl: Will challenge him for his females.
But Damian thinks this family is ready - so he and his crew put the final planks on the bridge. Then he tries to lure the gorillas over with, but of course, food.
[Damian on bridge throwing food yelling: "Come on! Come on!"]
Wouldn't you know it? The females venture out first. And once again, Djala follows their lead.
Lesley Stahl: Djala's going in.
Damian Aspinall: Brilliant.
Lesley Stahl: Oh my goodness. And look at the babies, the second one. Oh my gosh.
Damian Aspinall: That's wonderful isn't it?
That's one year old Akou. Within an hour, all 10 had crossed over.
Damian Aspinall: This is the ultimate goal--
Lesley Stahl: The ultimate goal--
Damian Aspinall: This is the Holy Grail.
Lesley Stahl: Although they will get on this side and inevitably face dangers that they're not really prepared for--
Damian Aspinall: Yeah. They will. The problem will be is when the other males turn up here. They have been quite near in the last few days. So I suspect they are quite near. And I suspect within a few hours, they'll be coming to investigate.
Lesley Stahl: Oh boy.
Damian Aspinall: Oh boy. Yeah.
If only we could end on an optimistic note. But we can't. A month after the gorillas crossed the bridge, Damian's team found all five adult females dead, including Tamki - as well as baby Akou. An outcome so many of Damian's critics predicted. So what does this mean for his experiment? We remembered what he said back in Kent.
Damian Aspinall: It may be a disaster. And if it's a disaster and they all die, all those people will jump up and down and say, "He was an idiot." Fine. I'm willing to take that. I don't care. I don't seek popularity. I'm the ambassador for these animals. I'm here to protect those animals and give them their chance to go back into the wild. 'Cause what I don't believe in is they should spend the rest of their lives in captivity.
Damian's best guess is that a wild male silverback attacked the family: killing some on the spot, others dying from injury, infections or stress. He called it "a hell of a setback" but is determined to send more gorillas into the wild.