captioning funded by cbs and ford. we go further, so you can. >> i am a muslim, i am an american, and i've been serving my country for 22 years and counting. and i am appalled at what these animals are doing to my country while desecrating my religion. >> his name is a national secret. his appearance, we have disguised. his true identity cannot be known, because he is an undercover f.b.i. operative who lives among the terrorists. >> it is part of what we do, though. we pretend to be someone we loathe, while hanging out with people we hate. >> animals with babies, always a

sure-fire hit at the zoo. >> oh, look. >> it's what all living creatures are biologically programmed to do-- mate, rear young, and pass their genes on to the next generation. >> is he a boy? >> but it turns out that behind every baby animal crowds flock to see and biologists want to protect, there is an elaborate mix of science, software... >> and that's a good pairing. >> ...genetics and moving vans. it's no longer the old-fashioned birds and the bees at the zoo these days. it's more like match.com. >> i'm steve kroft. >> i'm lesley stahl. >> i'm scott pelley. >> i'm anderson cooper. >> i'm bill whitaker. those stories, tonight, on "60 minutes." ♪ ♪

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>> pelley: tonight, an unprecedented interview with an undercover f.b.i. operative who secretly lives and works among the terrorists of isis and al qaeda. his name is a national secret, but, in 2012, al qaeda knew him as tamer elnoury. they thought he was a wealthy arab-american with seething anger at the united states. but as we first reported in october, in reality, he had dedicated himself to the war on terror the morning of 9/11. >> tamer elnoury: i remember thinking, "please, god, don't let this be a terrorist attack. please, god." and that's how naive i was. that's how naive we all were at

that time. >> pelley: tamer elnoury-- one of his many aliases-- immigrated from egypt as a child and was raised in new jersey in a traditional islamic home. >> elnoury: we're not at war with islam. we're at war with radicals. i am a muslim, i am an american, and i've been serving my country for 22 years and counting. and i am appalled at what these animals are doing to my country while desecrating my religion. >> pelley: devoted to islam and america, comfortable working alone amid killers, he was a rare find for the f.b.i.'s undercover counter-terrorism group. >> elnoury: it's called the national security covert operations unit. >> pelley: and what do the guys in the unit call it? >> elnoury: it's not the guys, it's me. i jokingly referred to it as the "dirty arabs group." >> pelley: the dirty arabs group? >> elnoury: yes. >> pelley: your bosses must have loved that. dark humor is part of the trade. in a new book, "american radical," he writes about

infiltrating terrorist groups at home and abroad. he wrote the book, he told us, so that fellow americans could understand how the islam he knows is tortured by terrorists trying to justify mayhem. we disguised him and changed his voice so he could tell us about one of the biggest investigations of his career. the target was a 30-year-old tunisian who was working toward a ph.d. at a canadian university. it was in 2012 that routine surveillance of chiheb esseghair's phone calls and travels gave canadian intelligence and the f.b.i. reasons to worry. >> elnoury: chiheb was talking to some really bad folks overseas. he made two trips to iran, and a handful of other int gathering evidence that was presented to us that led us to

believe that we needed to figure out who he was. >> pelley: esseghair had a visa to attend an academic conference in the united states, so the f.b.i. wanted tamer elnoury to dangle himself as bait just in case esseghaier was recruiting for al qaeda. what did you do then? >> elnoury: i crafted my legend, and made myself recruitable. i wanted him to choose me. i wanted him to go to bed that night wondering what he could do to become my friend. >> pelley: his legend, or false biography, was that of a wealthy arab-american real estate investor with a painful, private grudge. how did you meet? >> elnoury: we met on a flight from houston to san jose, california. >> pelley: not by accident? >> elnoury: we met on the flight from houston to san jose, california. >> pelley: that planned "accidental" meeting in june 2012 is called a "bump," as in, bumping into someone.

they boarded as strangers, and fate did the rest. >> elnoury: people were in his seat, people were in my seat. it was a legitimate mix-up. and as i was talking to the flight attendant, he noticed that i had a long beard, that i looked middle eastern and probably was a muslim. so, he poked his head over, and he said, "batakalem arabyi," which means, "do you speak arabic," in arabic. i said, "taba'an, assalmu alaikum wa rahmat'allahi wa barakatu." and he looked at me. and he said, "wa-alaikum assalaam wa-rahmat'allah," "i knew it." and then, the conversation proceeded in athher flight attendant and said, "we must sit together." he insisted. he chose me. >> pelley: the whole key to the thing is to make it their idea? >> elnoury: that's correct. >> pelley: what is the process

that you go through to get into one of these roles? >> elnoury: it starts that morning that i'm traveling, assuming i'm traveling covertly, in alias. i take a shower, and i put on, for this case, i put on tamer's clothes. i put on tamer's watch, his shoes. i drive tamer's car. his wallet's in my pocket. his phone is on me. and i drive to the beach, and i sit at the beach and i talk to myself out loud like a crazy person, reciting everything there is to know about tamer elnoury-- his company, his family, his legend, over and over. >> pelley: the f.b.i. created a history for tamer elnoury; an online presence, an actual office for his investment company where a receptionist answered the phone. there were ownership records, a home, fake i.d.s. and, critical to the legend,

there was a false personal tragedy. elnoury's fake background said that his mother had died of neglect in a u.s. hospital because of anti-muslim discrimination. that lie completed the picture of a wealthy arab-american who had a reason to hate. chiheb esseghair thought that his new friend was "made to order," which, of course, he was. for ten months, the men drew close. esseghair twisted the koran to justify attacking the west. he admitted that his trips to iran were for meetings with a senior al qaeda leader. surveillance showed that esseghair was checking tamer elnoury's back story. and one night, in a basement in toronto, elnoury was grilled by esseghair and three accomplices. >> elnoury: "what do you do? how do you do it? is it commercial real estate? is it residential? what do you do when you fly here? what do you do here?" it sounded like an

interrogation. >> pelley: this interrogation was so sharp, elnoury feared that his cover had been blown. he analyzed the room, in case he had to escape. but the cop within you had figured out where the exit was and had decided what order he was going to shoot the people in the room in, if it came to that? >> elnoury: oh, absolutely. at that point, as you get older and slower, you realize you always go for the young ones first. >> pelley: which leads me to ask, in all seriousness, where does the courage come from? >> elnoury: i can make the argument that you're probably more in danger crossing the street here in new york city than i am when i'm embedded in an al qaeda cell. if my legend holds up, i am worth so much more to them, safe. they protect me more than they protect their own, because tamer elnoury means access to the west. >> pelley: he passed the grilling and was enlisted in what al qaeda hoped would be its

long frustrated encore to 9/11. >> elnoury: he was planning on derailing a train from new york city to toronto. >> pelley: how was he going to do that? >> elnoury: well, that changed multiple times. it was either break up the tracks, use explosives. the bottom line was that train was getting derailed over a bridge that had as little water as possible, to ensure the deaths of everyone on that train. >> pelley: was this just some kind of pipe dream? >> elnoury: no, that was his tasking from al qaeda. >> pelley: the via-rail train carries hundreds of passengers from new york to toronto. in september 2012, esseghaier, elnoury and another man cased this bridge near toronto, the scene of the planned attack. as a surveillance team watched overhead, elnoury recorded chiheb esseghair explaining how the disaster would unfold.

it would seem that you have plenty to arrest chiheb on at this point. why does the investigation keep going? >> elnoury: because chiheb revealed to me that there was an american sleeper. he told me that there was an american version of him and that although he didn't know who he was, he was told by his trainers, al qaeda senior leadership, that they would put the two of them together when the time was right. >> pelley: there was an al qaeda american agent inside the united states? >> elnoury: that's what chiheb believed, and i believed him. >> pelley: the possibility of an al qaeda agent in america took the investigation in a new direction. tamer elnoury lured esseghaier loping leads. esseghaier asked elnoury to show him the sights, including times square. >> elnoury: he didn't see times square the way a foreigner would.

he saw it as an opportunity to kill americans. >> pelley: an opportunity, esseghaier suggested, for a future new years eve when more than 100,000 people would fill the streets. >> elnoury: multiple explosions that were timed about five to ten seconds apart. as one went off, he thought about where the crowd would then run to. and that's where he wanted the next bomb to go off. maximum carnage, maximum casualties. >> pelley: he expected to get away with derailing the train, so that he could go on to times square next? >> elnoury: exactly. chiheb said that al qaeda shifted gears. after 9/11, they lost some of their best minds. no more martyrdom. they didn't want to lose soldiers anymore, people with access to the west. so, you do what you can and get out, hide, and do it again. >> pelley: after his visit to times square, esseghaier wanted to see where the twin towers had

fallen. >> elnoury: and as he was wand me.his beard, and his arm he said, "tamer, this place needs another 9/11, and we're going to give it to them." i saw red at that moment. it was the hardest time in my career to stay professional. here i am on hallowed ground, and he said that to me. at that very moment, i could feel a pen in the pocket of my jacket. i envisioned stabbing him in the eye and dropping him dead right where he stood. >> pelley: you very nearly blew your cover? >> elnoury: yes. we do, though. we pretend to be someone we loathe, while hanging out with people we hate. maybe it was the culmination of everything that was happening,

the stress and pressure of identifying the sleeper. chiheb's rants about the west, whatever. but the point was, i almost broke that night. but thankfully for the case, i didn't. >> pelley: the f.b.i. wanted more time but, in april 2013, the boston marathon was attacked. and one week later, the canadian government insisted on wrapping up its al qaeda cell. chiheb esseghaier and the accomplice on the bridge were tried, convicted and sentenced to life, but the trail to the american sleeper, if he existed, went cold. >> elnoury: there hasn't been a day since april 22, 2013, when i've woken up-- no matter where i am-- that i don't think about the american sleeper. >> pelley: tamer elnoury's book, "american radical," was cleared for publication after an f.b.i.

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>> stahl: zoos have always been places where people come to marvel at, and connect with, the wonders of the animal world. but with more and more species endangered in their natural habitats, zoos have had to change their stripes. they have shifted their focus to conservation, and gone is the old practice of bringing in exotic animals from the wild. but without them, zoos today have to re-populate from within. and it's complicated. it turns out that behind every baby animal crowds flock to see, and biologists want to protect, there's an elaborate mix of

science, software, genetics, and moving vans. as we first reported this spring, it's no longer the old- fashioned birds and bees at the modern zoo. it's more like match.com. >> look at the baby. >> stahl: animals with babies-- always a sure-fire hit at the zoo. it's what all living creatures are biologically programmed to do: mate; rear young; and pass their genes on to the next generation. >> is he a boy? >> stahl: but you might be surprised to learn that long before the babies, and even long before the making of the babies, there is this... >> keith: we have three potential females that can move. >> stahl: ...a decidedly un-romantic meeting, in an unromantic-sounding place called "the population management center." >> amanda lawless: and that's a good pairing. >> stahl: in this conference room at lincoln park zoo in chicago, population biologists

like amanda lawless use computers to search out the best genetic matches for just about every zoo animal in north america. >> lawless: things like flamingos can have hundreds of animals. and, in a planning meeting, we are going to talk about every single animal in that population. so-- >> stahl: come on. you have-- if you have a meeting on flamingos-- >> lawless: yes. >> stahl: you're going to talk about every single individual flamingo in every zoo in the united states? >> lawless: yes. >> stahl: wow. >> lawless: so, some of these can take quite a long time. >> stahl: what this leads to is zoo animals traveling the country in search of love-- or at least a good genetic match. layla, the rhino in front, moved from kansas to chicago to mate with nakili, who seemed interested. >> hello. >> stahl: this marmoset monkey just flew in from omaha to meet her mate. and on the morning we visited, one of these warthogs was loaded into this crate for the nine-

hour drive to his new home, and prospective love interest, waiting in maryland. oh, they're eating! imagine transporting a polar bear. >> ron kagan: that's nuka. >> stahl: detroit zoo executive director and c.e.o. ron kagan can. >> stahl: so where did the male come from? >> kagan: he was born in denver, then went to pittsburgh, and then came here. >> stahl: did he go to pittsburgh to mate as well? >> kagan: yes. >> stahl: oh my goodness. he's-- a traveling-- swordsman. >> kagan: well, that's what we do. >> stahl: it began back in the 1970s, when zoos largely stopped getting animals from the wild and had to learn to manage their populations themselves. they came to realize that one major risk in a closed system, says geneticist bob lacy at the chicago zoological society, is inbreeding. >> bob lacy: the simple thing to do if we were breeding animals would be, for example, to have 100 giraffes in zoos and just let them breed on their own. the problem with that is if we did that, probably five or ten of the males would be good

breeders, and they would exclude the other males from breeding, and we would very rapidly have a population where everyone is closely related to everybody else, and therefore we would lose diversity. >> stahl: lose diversity, meaning genetic diversity, since all the other giraffes' genes would be lost. so lacy and a few colleagues developed software now used worldwide to assess animals' lineages and calculate ideal couplings, to make sure all genetic lines remain in the mix. can i call you the father of computerized animal dating? >> lacy: ( laughs ) >> stahl: but it is computerized dating, and we smile about it-- >> lacy: it is, yes. yes, it is. >> stahl: --but it really is. that's, that's what you're involved in-- >> lacy: and in ways-- well, i don't know much about human computerized dating, but in ways that are probably comparable, that we have to look at a lot of different factors. not only inbreeding, but social compatibility, age differences, how far away they would have to move. >> lawless: so we'll have those three transfers... >> stahl: lawless and her team use lacy's software every day.

she gave us a mini-tutorial... can we look at gorillas? >> lawless: yes. >> stahl: ...starting with a list of every gorilla in an accredited zoo in north america. louisville, atlanta, milwaukee, cincinnati. for each gorilla, there is basic information. >> lawless: so, that's its parents. >> stahl: the father, the mother, birthday. a complete family tree, tracing its ancestry all the way back to the wild. oh, that's so interesting. and most importantly, this genetic ranking, done by an algorithm, with males on the left, females on the right, that rates each animal by how rare its genes are, and therefore how desirable. >> lawless: so you can see little rock has the fourth most valuable female. >> stahl: it then tells you the genetic value of any pair ofanye of one to six. >> lawless: so you can see, when we pair these two animals, that two is still valuable. >> stahl: all the way down to sixes, which she says should never breed.

can i try? >> lawless: yes. so all you have to do is click anywhere... >> stahl: i have to say, it was oddly thrilling to be a gorilla matchmaker. look what i just did. i found you a one. my pair was a male from dallas, and a female from columbus. it seemed to be very promising. i'm feeling so good about this. ( laughs ) but she said we still had to check a few details. >> lawless: okay, the age. we didn't just pair up a two- year-old with a 20-year-old, did we? and we didn't. so she's 17, he's 21. >> stahl: next, we'd have to check on their temperaments and compatibility. will they get along? >> lawless: will they get along. >> stahl: if so, they could end up here, in what are called breeding and transfer plans-- species-by-species reports the population management center sends to every zoo... oh, and here are the rhinos. oh, what are these, beetles? >> lawless: yeah, so that's-- >> stahl: you have a whole book for beetles? >> lawless: yes. >> stahl: ...telling them literally what every single one of their animals should do, with whom.

>> lawless: so, we want 2735 to breed with 2764, because that's a genetically valuable pair. >> stahl: valuable not because their genes are special somehow, but because they're less common. but what about species that live all together in big groups-- like penguins, or flamingos-- so zoo managers can't control who pairs up with whom? well, there's a system for that, too, says lincoln park zoo's executive vice president megan ross. >> megan ross: what we do is we put together a grid where the females are on one side, and the males are on the other. and then, for each pair that could possibly happen in that flock, we have a recommendation. >> stahl: again, "one" for the best genetic matches, down to "six" for the worst. so what happens if the pair that's six, wants to breed, or tries to breed? >> ross: we might do egg management, where we might take the egg and replace it with a

dummy egg so that their eggs would not hatch. >> stahl: you actually go in and take their egg and replace it with a fake egg? >> ross: we do. >> stahl: we witnessed "egg management" in action. the keeper, creeping in with a basket of dummy eggs, and notes on which birds have partnered up. she checks to see which pairs laid eggs overnight, then makes a switch. when you take an egg away and put in that dummy egg, are they not aware that the dummy egg is not their egg? >> ross: as far as i know, they do not realize that we have swapped their eggs out. >> stahl: they sure didn't seem to notice. and how's this for egg management? this pair of european white storks used to get high genetic ratings, but they have had so many babies, their genes are now too common. so when they laid another egg last year, the zoo took it, and

gave them someone else's-- the egg of a genetically valuable but inexperienced pair of storks from cleveland. >> ross: the stork parents at cleveland metropark zoo were not really attending to the nest in a way that we thought they were going to be good parents. so they sent their egg to us, and we swapped out the eggs. >> stahl: you brought a fertilized egg here to chicago, from cleveland? >> ross: we did. >> stahl: it hatched last may. >> ross: and now this pair is actually rearing another pair's chick. >> stahl: do they know it's not theirs? >> ross: i don't think so. >> stahl: so, stork foster parents. >> ross: you probably thought they just delivered the babies. >> stahl: ( laughs ) your program-- to create this genetic diversity, requires an enormous amount of cooperation. and i was under the impression that zoos compete. they compete for the panda, they compete for exotic animals. >> lacy: yeah. >> stahl: are zoos not competing any more? >> lacy: zoos are still competing. you know, zoos compete for

audience, for publicity. for all kinds of things. but someone gave me a good example the other day of baseball teams. obviously, baseball teams compete, but a single baseball team on its own is pointless. it can't do anything. >> stahl: yeah, you need a league. >> lacy: the same thing's true of zoos. if zoos were all independently operating and not willing to work together, we would all sink. our populations would die out on us. they would become highly inbred. so we do compete in a sense, but we recognize that we will all succeed in conservation together or not. and zoos are now working on conservation with wildlife agencies as well, to rescue wild species in distress, like the mexican gray wolf. these wolves once lived across the southwest, but were viewed as predators and killed off. >> lacy: so, by 1980, they were gone from the wild-- >> stahl: i mean, seriously gone? >> lacy: they were gone. >> stahl: the u.s. fish and wildlife service brought the last remaining wolves to zoos, to see if they could pull off a miracle and bring the species

back from just seven, what biologists call "founding," animals. >> lacy: so we used the computer analyses to decide exactly which animals should be bred each year, how many to breed, so we didn't lose any of those seven lineages. >> stahl: and it worked. is that a pup? oh yeah, okay, i see it. >> lacy: and from those seven, they've increased numbers up to, now, about 250. and they've been releasing them in the wild for about the last 20 years. >> stahl: wow. but zoo geneticists are still at it. last spring, when litters of puppies were born here at chicago's brookfield zoo and in the wild, zoo staff took two of the newborns from here and switched them with two from the wild pack. to make sure the mothers wouldn't reject them, the staff coated the pups with dirt and urine from the dens they were going to. the mothers in both packs are now raising the exchanged pups as their own.

we saw, with storks, that they swap the eggs-- >> lacy: right. >> stahl: but you're actually swapping the actual pups. >> lacy: the pups. because the wild has so few animals, that if we didn't do some swapping, they wouldn't have any appropriate mates. so we swap between zoos and the wild just the way we swap between zoos. >> stahl: but zoo genetic matchmaking isn't just success stories. there are dilemmas and moral quandaries. how do you stop animals with "do not breed" recommendations from mating? and what happens when animals breed too well, and zoos don't have enough space? they can't just make them disappear... or can they? that's where our story takes a surprising, some would say darker turn, when we come back.

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>> stahl: zoos around the world have adopted genetic breeding programs similar to the one in the u.s. as a result, many species are breeding better in captivity than ever before. but that success has brought challenges, and differences of opinion. case in point: how to manage animals who don't get a breeding recommendation-- animals whose genes are already well-represented in zoos? one radical solution: culling them-- killing them. that's what the copenhagen zoo in denmark did a few years ago with a healthy, two-year-old giraffe named marius, and it caused an international uproar.

a warning: this part of our story contains some difficult images that young children may not want to see. but first, the preferred american solution for zoo animals who aren't supposed to breed. >> see one? gorilla! >> stahl: rollie is a 21-year old gorilla at the lincoln park zoo in chicago. every afternoon, she and the other gorillas here get a snack. being gorillas, they don't bother to unwrap it. but unbeknownst to rollie, hers has something special mixed in. rollie is on the pill. >> ross: our gorillas take the birth control pills every single day. >> stahl: the same stuff we take? >> ross: the exact same stuff that we do. >> stahl: come on. >> they all have their packets. >> mike adkesson: so ours actually come from walgreens. >> stahl: no. >> adkesson: yeah, same 28-day pack. >> stahl: mike adkesson is the chief veterinarian at chicago's brookfield zoo. for all what-- the gorillas? chimps? >> adkesson: gorillas, chimps,

orangutans, our gibbons. >> stahl: look, walgreens. >> adkesson: walgreens. >> stahl: look at that. who knew? >> adkesson: yeah. >> stahl: aww, look! and that was just the beginning. turns out, all kinds of zoo animals use all kinds of contraception. she got a "no breed" recommendation? >> adkesson: she got a "no breed" recommendation. >> stahl: this monkey, anesthetized for her annual physical, was getting a birth control implant between her shoulders. >> vet in detroit: her dose is two, because she's big. >> stahl: at the detroit zoo, there was an aardvark getting a birth control implant in her leg. now there's a sentence one never expects to say. and then there was dr. adkesson's next patient... oh, my! hello. what a strange-looking creature you are. ...a furry fellow called a rock hyrax, who dr. adkesson says is somehow related to an elephant. >> stahl: what? >> adkesson: yes. from an evolutionary standpoint, closest relative is the elephant.

>> stahl: no. elephant or not, he too was getting a contraceptive implant. >> adkesson: it's about the size of a grain of rice. and this plunger's just going to push it out under the skin. >> stahl: but not everyone thinks putting zoo animals on contraceptives is a good idea. look at those eyes. they're huge. at the copenhagen zoo, which participates in a european genetic breeding program, they have a different philosophy. here, as bengt holst, director of research and conservation told us, they're against birth control. they think animals should be allowed to breed and raise their young, just as they would in the wild. do you think that there's an ethical issue when it comes to not allowing animals to breed? >> bengt holst: yeah, i think so. >> stahl: to raise their babies? you think it's ethical? >> holst: yeah, i think-- i think it's ethical, because that's actually a big part of their-- their normal behavior. parental behavior is a 24-hours job for one year, two years, three or four years, depending on the species. and we should not take that away. >> stahl: but that means

offspring, who need new homes in other zoos once they reach adolescence, and it gets tricky. >> holst: the female cannot grow up here in this zoo, because then she will mate with her father. >> stahl: so the father would mate with his own child? >> holst: if she stayed here until she got mature, then he will start mating her. >> stahl: it's not that difficult to place young female giraffes in other zoos, because giraffes live in harem groups, where one dominant male lives and breeds with several females. but for young males, it's tough, particularly for ones whose parents have bred well, so their genes are not considered valuable in the breeding program. that's what happened to marius-- and this is where our story takes that dark turn. born at the copenhagen zoo six years ago, marius needed to move when he reached the age of two and did what adolescent male giraffes do-- start challenging their fathers, trying to take over the harem. >> holst: we could see that they

had started fighting. and-- i mean, at the beginning, it's just a little bit pushing around. but then at-- at some stage, he started getting scratches on the side, because the father had pushed him up against a tree and had really hit him hard. and if we have left him with the father, he would have killed him, i'm sure. >> stahl: in the wild, this is when marius would strike out on his own, a time when in nature, many animals are killed by predators. but in the zoo, there was nowhere for him to go, and with no spots for him in the european breeding program, the zoo thought their only choice might vebe so uggestions t of what to do, short of killing this beautiful animal. some people said, "why not just release him in the wild?" >> holst: yeah, we cannot just release a giraffe into the wild. it would be killed immediately, because all space is occupied by other giraffes. >> stahl: i know there was a very wealthy american who offered to take marius. >> holst: but for what reason? he will keep a single giraffe,

which is a social animal. that will be really bad welfare for this giraffe. we will never send an animal to a place where it won't have a good life. >> stahl: so on a cold february morning, the zoo went ahead and ended marius' life. >> he was shot dead yesterday by a veterinarian. >> stahl: marius' death got worldwide attention, and condemnation. >> judge jeannine pirro: you should all be ashamed of yourselves! >> stahl: here you tell us that zoos are there to save the animals and protect animals. and then the zoo kills an animal. >> holst: but that's exactly what we do. we protect animals. we protect animal populations. and in order to protect animal populations and make sure that they are healthy, also far into the future, we need sometimes to take some animals out of this population. normally, we have nothing against killing healthy animals in the wild. i mean, in america, you hunt deer. in denmark, we hunt-- >> stahl: well, some people hunt deer... >> holst: some-- yes, but you eat meat. most people eat meat. and meat comes from live animals.

>> stahl: if it's killing or contraception, isn't the contraception better than the killing? >> holst: no, i don't think so, because contraception-- by contracepting the animals, you take away a huge amount of their natural behavior. >> stahl: as opposed to their life. >> holst: decreasing their welfare. we need to give an animal a good life. no animal has an expectation of, "i can become 20 years old or ten years old or two years old." animals live in the present. the important thing must be to have a good life as long as they live, be it two months or 20 years, doesn't matter. >> kagan: killing a healthy animal is killing. it's not euthanasia. >> stahl: ron kagan, from the detroit zoo, adamantly opposes culling. he says the focus on genetics and saving c >> kagan: we have assumed 100% responsibility for the life of those animals that live here. so, for us, we're concerned with individual welfare, not just conservation. >> stahl: under pressure from animal rights activists, and those who think animals

shouldn't be locked up at all, zoos have tried to improve the quality of life of their animals, and kagan's been a leader in that effort. back in 2004, detroit was the first american zoo to give up its elephants for ethical reasons, when kagan says it became clear they were suffering in the cold climate. and he's worked to create larger and more natural habitats for the animals. >> kagan: i want every individual animal that lives here to have a great life. >> stahl: but he would say the same thing. >> kagan: well, you-- it's pretty hard-- >> stahl: and the good life includes pregnancy and-- >> kagan: right. >> stahl: --giving birth and so forth. >> kagan: well, the idea that you say you should be able to have a baby, but then you're going to kill it. i honestly, that-- it's very hard for me to see how that works on any level. i don't want to kill healthy animals. >> stahl: how about dissect them? the day marius was killed, the zoo conducted a public autopsy--

considered educational in denmark-- then fed what was left of his body to the zoo's lions. the autopsy-- done before the public, with little kids standing right there. now, you got a lot of criticism for that. >> holst: yeah, that's right. you have to realize, first of all, that this is normal in denmark. that we do open dissections of animals. it's because we believe that animals are fascinating, but not only when they are wandering around on the savannah, but also if you open them up, because then suddenly you can explain some of the biology. for example, why is the heart of a giraffe that big, whereas yours and mine is just like a little apple, or big apple? that's of course because the heart has to pump the blood five meter up in the air. you cannot do that just by looking in a book. there was a big crowd watching. it was bitterly cold that day, but they stayed because they were so fascinated by it. and the kids, they really-- i would claim they loved it. >> stahl: you fed marius to the lions.

>> holst: after we did the autopsy, we have a little bit more than 200 kilo of meat left. should we just throw out this meat and then kill a cow in order to feed the lions? so we take another good life? or should we use the meat that was there already and feed it to the lions? >> stahl: why was that done before the public? >> holst: why not public? because we have nothing to hide. this is just natural that an-- lions eat meat, and lions eat giraffes. >> stahl: because you want the public to support not only your zoo, but other zoos. and people don't want to know-- >> holst: yes, they do. people want to see these things, because that's normal and that's natural. and i think if we hide it, we do a really wrong thing, because then we show people a wrong picture of what nature is really about. >> stahl: while not alpe zoos practice culling, it is association rules, which call it "one of a range of scientifically valid solutions to the sustainability of animal populations in human care."

>> how do they sleep? >> stahl: so what about zoos on this side of the atlantic? the a.z.a., the association of zoos and aquariums, do they ban culling in the united sta-- it's not banned? >> kagan: no. >> stahl: is it done in the united states? >> kagan: we don't do it. >> stahl: i know you don't do it, but do other accredited zoos? >> kagan: i don't know. >> stahl: it's possible? >> kagan: it's possible. >> stahl: it's a touchy subject, but it is being discussed. two published papers in the journal "zoo biology" explore possible advantages to selective culling, and point out problems with widespread use of contraception. birth control long-term can have harmful side effects, and keeping animals from breeding can cause fertility problems later on, if their genes are needed in the mix. >> stahl: so in other words, it's all a trade-off. >> kagan: i think that's exactly right. life is filled with compromises. it's filled with compromises in the wild, and it's also true in a captive environment.

so for instance, we want animals to have as much control and choice as possible in their daily lives. having said that, they obviously don't have the choice to leave the zoo. and we don't let our tigers kill living animals. and that's a trade-off. >> stahl: speaking of trade- offs, we noticed that the detroit zoo has a young male giraffe over the age of two who is still living with his family, because a transfer plan had fallen through. so why isn't he fighting with his father? well, get this: so what was your solution? >> kagan: so he was castrated. >> stahl: was castrated. >> kagan: right. so, that way he can stay with the group. and he's perfectly healthy and happy, just like people's dogs and cats that, you know, are spayed and neutered. is it ideal? no. >> stahl: back in copenhagen, there are now two young giraffes-- a half-sister and

brother to marius. we couldn't help but wonder about their future. is it possible that one or both will have to be culled? >> holst: for the male, it may be an option, yes. >> stahl: marius ii. >> holst: could be, yes. we still have 15 months to look for a place for him. but if necessary, we will do it, yes. >> are zookeepers playing god? a conversation with lesley stahl at 60minutesovertime.com. ♪ a wealth of information. a wealth of perspective. ♪ a wealth of opportunities. that's the clarity you get from fidelity wealth management. straightforward advice, tailored recommendations, tax-efficient investing strategies, and a dedicated advisor to help you grow and protect your wealth. fidelity wealth management.

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>> whitaker: 50 seasons of "60 minutes." tonight, from 1981, when harry reasoner offered an ode to a then-38-year-old film he maintained was "the best movie ever made." >> reasoner: that's why we had them haul out the props from "casablanca" at the burbank studios in hollywood, all the artifacts from that old imaginary love. love affairs in the movies that turn out happily become "the

thin man" or astaire and rogers. the great ones always have some tears behind the smiles. remember a piano, and this lamp, and the lovely girl sitting at the table, and both the memory of love and the foreshadowing of despair? ( ♪ "as time goes by" ) ( ♪ "as time goes by" ) >> whitaker: here's looking at you, harry. i'm bill whitaker. we'll be back next week with another edition of "60 minutes."

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