The Weekend's TV: Sperm Whale: Inside Nature's Giants Special / Sun Channel 4, Ronnie Corbett's Comedy Britain / Sat ITV1

Whale of a time with the monster bunch

"I know him not," says Ishmael, the narrator of Herman Melville's Moby-Dick, "and never will." The best documentaries about the natural world reveal more about what we don't know than what we do. Together with the sheer majesty of the species dissected, this is what made Sperm Whale: Inside Nature's Giants Special one of the outstanding nature documentaries of recent years.

And that despite an inauspicious setting. In March, a sperm whale was beached on the craggy sands of Pegwell Bay in Kent. Taupe skies gave a grimness to its final setting, but veterinary scientist Mark Evans, who looks like the sort of person you'd back in a fight with a cobra, saw this as a marvellous opportunity. He and the producers called in a garrulous anatomist called Joy Reidenberg, who soon emerged as the star of the show. In a 20-hour burst, first under floodlights and later fighting the tide, they went digging into Leviathan.

Cetacea, the order that includes whales and dolphins, comes from the Greek ketos, meaning "sea monster". That is how whales were thought of for long, with a vast incongruity between their size and our tiny understanding of them. Whales were first filmed under water only in 1975. Sperm whales can be around 20m long, weigh 60 tonnes, have probably the biggest brain of any animal and produce the loudest noise – over 200 decibels and audible to human ears nearly 40 miles away. The have a prehensile penis and a nose that must strengthen the otherwise silly case for intelligent design.

They are so named, we discovered, because the spermaceti (a wax-like substance) stored in their vast head, which constitutes a quarter of the body, looks like semen. This substance, sometimes called whale oil, provided the smokeless flames that lit Victorian England. Naturally, the producers had sympathy for the plight of the species at the hands of man, but thankfully the misanthropy wasn't laid on too thick. Instead, the further we dug inside this enormous, fresh cadaver, the more fascinating the biology lesson became.

Sperm whales have so much blubber because they need to withstand extreme cold and high pressure at the bottom of the ocean, where they find food. At these depths they can get down to one or two heartbeats per minute. Possibly their most amazing feature is a nostril that both breathes and, through a set of inner lips, sends a giant noise rebounding through the head, emitting from the front of the nose. This "clang" is the loudest language known life can produce.

There was a dual narrative between Evans and a chap called Simon Watt, who was off speaking to experts about all things whale. Richard Dawkins had a walk-on part too, narrating a few diagrammatic asides. At times, it felt like two shows were being forced into one, but that could be forgiven because of how beautifully directed the beach scenes were.

The gruesome adventure into blood and blubber on Pegwell Bay had a kind of nobility. Science itself was on the march here, entering a bodily universe in search of clues about life in our oceans. The ultimate hero was the nameless whale, and by the time its hacked body was conquered by the tide, gleaming puce and silver, we had the abiding consolation of a life donated to human knowledge, which is not a bad thing for a sea monster to achieve.

Size has always been central to Ronnie Corbett's fame too – or rather, the lack of it. As if to prove the point, Matt Lucas described him as "a giant" in the introductory sequence of Ronnie Corbett's Comedy Britain. That sequence made this sound like a long and slightly tedious tour of Corbett's lunch companions, with the aim of presenting him as the patron saint of British comedy. In fact, it was utterly wonderful.

Miranda Hart, Stephen Merchant, David Mitchell and John Cleese were among those who shared insights into what makes comedians tick and comedy funny. The former is mainly the potential for going from bladder-wrenching insecurity to megalomania in the blink of an eye. The latter is mainly timing.

Corbett proved a superb and humble interrogator. He didn't address the decline of the sitcom and the relative rise of sketch shows, nor did he ask why so many comedies these days centre on flocks of people, rather than families, and what that says about our society. But he did remind us that contemporary British comedy is full of great talent, a useful corrective to the nostalgic defeatism of most televisual trips down memory lane.

a.rajan@independent.co.uk; twitter.com/amolrajan