This truth will forcefully be brought home later this year with the release of a film that has not only shed new light on one of the most distinctive groups of birds, but which has also become the surprise box-office smash hit of the summer in the US.
March of the Penguins is a low-budget movie with a big impact. Directed by a French biologist, Luc Jacquet, this wildlife documentary cost a mere £4.5m to make, but is putting more bottoms on American cinema seats than the Steven Spielberg/Tom Cruise epic War of The Worlds, which cost £100m.
It focuses on the remarkable life cycle of the emperor penguin, Aptenodytes forsteri, the largest of the 17 penguin species, all of which are found in the southern hemisphere. The emperor is the southernmost species of all: it breeds on the ice-bound Antarctic land mass.
Just what it takes to do this is made rivetingly clear in the 80-minute film. At the end of the Antarctic summer, in March, the birds flop out of the waters of the Southern Ocean where they have been assiduously feeding, and begin a long trek to their mating grounds. Thousands gradually come together, tramping over the ice in long single files like patrols of infantry. The sight is mesmerising, for the march of the penguins is up to 70 miles.
When at last they reach their mating grounds on the ice, courtship begins, or, as the publicity from distributors Warner Bros has it, "in the harshest place on Earth, love finds a way." The birds mingle and chatter, with females choosing males after distinctive mating rituals captured by Jacquet and his two cameramen, who spent a whole year with the birds.
As one book on penguin behaviour puts it, "before copulation they face each other, and bow several times." Then they pair up, monogamously, to face the trials ahead. And what trials they are; for the breeding season of the emperor penguin is the Antarctic winter. As the six-month dark descends and the thermometer drops with it, to minus 60 and even lower, the female bird produces an egg - and promptly departs. The effort has been so great and she has gone without nourishment for so long - up to seven weeks - that now she must return to the sea to feed.
The task of incubating the egg in the harshest conditions on earth now falls to the male . When blizzards arrive, with 100mph winds in a nightmare of frozen dark, even these birds adapted to the conditions through millions of years of evolution have to huddle round together in great groups to keep a minimum of warmth: they look like German prisoners of war in their greatcoats, shuffling sullenly across the icy steppe.
But most survive, and so do their eggs, kept secure and warm in a fold of abdominal skin just above their feet; and after 60 days of this, the eggs hatch. The male feeds the tiny chick at first with a milky substance, then the female returns to take over, recognising her mate by call.
But success is not automatic; if the female is late back - or falls prey to leopard seals or killer whales in the water - the male has to leave the chick and return to the sea himself, or he will starve to death. (The underwater shots of the birds - streamlined fish-hunting torpedos in the water, in contrast to their awkwardness on land - are magnificent.)
March of The Penguins is narrated by Morgan Freeman (who also narrates War of The Worlds), and it is a success on two levels: firstly, by revealing this remarkable saga of life on the very edge, and displaying it in stunning colour images; and, secondly, by triggering huge waves of sympathetic emotions in the viewer.
The 37-year-old Jacquet has been a biologist and film-maker for a dozen years, specialising in the Antarctic: an earlier film was about the ferocious leopard seal. He says he feels at home in the ice. "I feel particularly comfortable in the polar environment," he said in a recent interview for National Geographic. "One gets a real sense of adventure there. Yes, you encounter a lot of difficulties. But once you stay there, your body somehow adapts. Over time you learn to deal with the terrific wind, which in some ways is worse than the cold, and you learn to minimise movement."
Asked why he thought Antarctica was so beautiful, he said: "It's indescribable. It's almost not like Earth. It's such a challenge to transmit via film the sensations you feel over there. The scale is just mind-boggling. You have icebergs that are 30km wide. It's a strange environment... there's no human reference-point for it. There are only two colour schemes.
"I wanted to tell things more as I felt them, rather than try to describe them as a scientist. It's about the struggle between life and death. It explores the outer limits of what is possible for a creature to experience. The penguins live where no other creature can. How do they do it?"
Because they're tough. His film proves it. Getting into the SAS might be hard, but getting into the emperor penguins, if there were a selection test, would be much harder.
'March of the Penguins' is due to be released in the UK later this year