A fluffy polar bear cub called Knut, who has become a media celebrity, should be given a lethal injection according to German zoologists, who say he has become too dependent on humans.

Their controversial claims have provoked a public outcry and a debate about the treatment of zoo animals.

The male cub is the first baby polar bear to survive in Berlin zoo for 30 years. After he was born on December 5 last year, his mother, Tosca, a grumpy 20-year-old former East German circus bear, put Knut and his brother out to die on a rock in the bear pit. Keepers scooped the cubs out of the compound with a fishing net and placed them in an incubator.

Only Knut survived, and was fed with human milk and cod-liver oil every half hour. In the Arctic, the minus 35C (-31F) temperatures destroy viruses and bacteria and make it easier for cubs to live. Knut has been brought up as a pampered baby. He is fed chicken purée, was given his own Christmas tree, sleeps with a teddy bear, plays with a football and his pony-tailed keeper strums Elvis Presley songs to improve his mood. The keeper, Thomas Doerflein, says the cub falls asleep when he sings You’re the Devil in Disguise.

The German capital has made Knut into a kind of mascot and even quality newspapers have been keeping a regular Knut diary. “We Need You Knut”, says graffiti on walls. The zoo has allowed Annie Leibovitz, the New York photographer, to snap the cub for an international anti-greenhouse-gas campaign to illustrate the melting of the icebergs. Out of 70 cubs born in captivity over the past 50 years, only 34 have lived. Now it could be curtains for Knut.

“Hand-feeding is not appropriate to the species and is a grave violation of the animal protection laws,” said Frank Albrecht, an animal rights campaigner. “Legally speaking, the zoo should kill the baby bear. Otherwise it is condemning the bear to a dysfunctional life and that too is a breach of the law.”

The director of Aachen zoo, Wolfram Ludwig, also believes the Berliners made the wrong decision in saving Knut: “It is not correct to bottle-feed a small polar bear. He will always be fixated on his keeper and will never grow to be a proper polar bear.” Knut, he argues, should have been killed when Tosca rejected him. “One should have had the courage to kill him much earlier.”

Leipzig zoo showed the way last December by injecting a rejected baby sloth with T61, a poison that kills in two seconds. The argument used by Leipzig and specialists such as Rödiger Schmiedel, the head of Germany’s Bear Foundation, is that it is impossible to domesticate a wild animal so it is better not to start. But the “save Knut” faction could yet win the day. The cub is due to be presented to the public this week after reaching the critical weight of 8kg (18lb), at which he is deemed strong enough to face TV cameras. It will then be even harder to dispatch him quietly with a T61 jab.

“The humanisation of this bear has to stop as soon as possible,” said Wolfgang Apel, the head of the German animal protection league, “but he has a right to live.”

The battle for Knut comes when zoos are debating whether they have a new responsibility in the light of climate change, especially towards Arctic species. If Knut grows to maturity he could reach 500 kilos. The question is whether Knut’s offspring would be capable of independent life or whether they too would be dependent on human support. Crowds gathered in front of the polar bear pit yesterday in the vain hope of seeing Knut.

What they did see was Tosca with her partner, Lars, raising the prospect of more cub-trouble. “What do you expect?” an irritable keeper said. “It’s spring in Berlin.”

Born to be wild

— The polar bear is the world’s largest terrestrial carnivore

— It can eat up to 50kg (110lb) of fat in one meal

— In Canada seven people have been killed by bears in the past 30 years

— They devour the skin and fat of prey before the meat

— Bears’ stomachs make up between 15 and 20 per cent of their body weight

— They hunt seals by waiting next to an air hole for their prey to surface, then biting into its head

— The bears have 42 teeth, some up to 1.5in long. They are used to rip off blubber and flesh

— The teeth are not normally used for chewing as polar bears prefer to swallow whole chunks of meat

Sources: Polar Bear International, Seaworld, National Geographic

Times Recommends

• Over the Wall
• Why Africa welcomes the ‘new colonialism’
• Which will come out on top: paper or gold?