Last Night's Television: The Secret Life of Twins, BBC1<br /></b>The Art of Dying, BBC4

I've had problems before with Chris and Xander, two male doctors who first popped up on Channel 4 in a series called Medicine Men and are now fronting up The Secret Life of Twins, a BBC1 series about what we can learn about nature versus nurture from biology's very own buy-one-get-one-free offer. There's nothing wrong with either of them incidentally: they look good on screen and they have a kind of easy-going manner that makes them a good anchor point for a popular- science programme. The problem is that they're identical twins, which makes it tricky to attribute the quotes properly. Was it Chris or Xan who expressed the hope that genes wouldn't turn out to be "an iron cage that constrains all your choices"? And was it Xan or Chris who insisted, in a comically pushy manner, that his counterpart was "a bit more pushy than me"?

It doesn't greatly matter in the larger scheme of things I suppose and Chris and Xander's status obviously gave them an edge when it came to the programme's central subject, which was the way in which identical twins offer clues as to how our characters and our bodies are formed. Whenever large groups of identical twins are gathered together – as in the annual festival in Twinsburg, Ohio, or the twins summer fête at St Thomas' Hospital, which featured here – scientists swarm around them like wasps at a picnic, hoping to pin down the genetic component for everything from pain resistance to susceptibility to alchohol. And for these white-coated wasps, the jam to beat all jams is a pair of separated identical twins, born as clones but raised in entirely different circumstances.

Twins like Alexandra and Mia, two Chinese orphans who had been portioned out by the Chinese authorities to Norwegian and American adopters. Suspecting the truth, their respective parents had done DNA tests and had their suspicions confirmed, and the programme included a touching sequence in which the two little girls met again, their shared genetic code almost immediately triumphing over the gulf of language and experience that now separated them. That was one finding here. You – or your parents – may think that environment and upbringing will mould the raw genetic material, but the raw genetic material has ideas of its own. Spare a thought for Iain Southerthwaite, an expat Englishman who lived a life of blameless nutrition and exemplary exercise in New Zealand and yet succumbed to the same arterial clogging as his pie-eating, tab-smoking, pint-quaffing twin back home.

Like Chris and Xan, Dan Cruickshank had a direct personal stake in the subject matter of the programme he was presenting, but then we all do because it was The Art of Dying, another of the BBC's attempts to send us with a bit of top-spin into a national bout of Seasonal Affective Depression. If programmes had to be named on the basis of the images that predominated in them then this would have appeared in Radio Times as "Dan Cruickshank Stares Out of the Window", because it was a daringly contemplative affair, filling startling amounts of its hour-long slot with pensive gloom. This doesn't entirely do justice to Matthew Hill, the director, because in some ways this was an object lesson in how to make an unsatisfactory programme beautifully. There were lovely, thoughtful shots in it, and some effective visual metaphors for the erasure and enigma of death, including the downbeat Caspar David Friedrich with which Hill ended his film – Cruickshank staring out over a drizzly sea as if hoping to catch some clue as to what lay over life's horizon.

But it wasn't easy to work out exactly what the programme was supposed to be doing. The title (and the trails) seemed to suggest that it was about how artists help us to understand the mystery of death, but if so it was a very desultory survey, looking at a mere handful of examples. And if – as was alternatively proposed from time to time – it was one man's journey towards an acknowledgement of his own mortality, it was never entirely clear what we stood to gain from accompanying him on the trip. His eloquence tended to abandon him at the critical moments, as when he visited the office of the BBC's obituaries editor to read a less than unequivocal 700-word survey of his own life and career. "Umm, urrr, wow... err," he said, absorbing the stinging fact that John Tusa's attack on him as the very epitome of dumbing down was to take up at least 20 of those words. By the time he'd staggered on to a nearby stairwell, to gaze mournfully out of yet another window, he appeared positively suicidal: "Nothing lasts," he said glumly. "Let alone our own pathetic little lives." Cheers, Dan. Personally, I can't see what's so terrible about living in a state of denial about death. It's only doing to it what it's eventually going to do to us.