The Weekend's Television: Young, Dumb and Living Off Mum, Sun, BBC3; On Thin Ice, Sun, BBC2; Rivers with Griff Rhys Jones, Sun, BBC1

There seems to me to be an essential flaw in Young, Dumb and Living off Mum, a BBC3 series in which eight unweaned young people are torn from the parental teat and forced to look after themselves in a south London house. Each week the participant who has delivered the feeblest simulation of maturity is voted off the show by a panel of their parents while the remaining members stay on to compete for the prize of a round-the-world trip. And, given how infuriatingly feckless those taking part are, this seems to get the carrot-and- stick ratio seriously wrong. Surely it should be the other way round. The ones that show themselves halfway capable of adult life should get early release for good behaviour, while the monsters are forced to stay, battling to avoid the grand prize of a season's work as a deckhand on an Arctic crab boat. Given their terrors of even the smallest personal inconvenience I suppose they would have all simply walked out in week one – but barbed wire and Tasers don't cost that much.

On the other hand, perhaps it's not the inmates that deserve the punishing. If you've got a 25-year-old still living at home, demanding an "allowance" and scornfully contemptuous of the idea that they might justify their existence in any way, then you've probably played a sizeable part in making them that way. It's not that these people are incapable of grasping the abstract concept of responsibility. It's just that they have never been required to exercise the muscles. So you get dim, blurry approximations of what it might look like to behave in a grown-up fashion. Rachel, a puffy amalgam of smeared mascara and backcombed hair, groggily explains that she only goes out and gets hammered two nights a week and that on the other nights she keeps her drinking in check – advancing this as a measure of her self-control. Dina, who thinks herself a prodigy of self-reliance because she can make instant soup, is puzzled when she attempts to do it from scratch: "I thought you just put peas in a pan and they melted," she says, jabbing disconsolately at the pan with a potato masher. Frankly it's surprising that they can wipe their own bottoms – though the state of the house lavatories suggests that some of them might still be grappling with that lowest common denominator badge of independence.

Their task this week was to put on a fashion show, a challenge one team achieved perfectly creditably while the other team, handicapped by people whose egos have had an extra four or five years to calcify into selfishness, fell apart. Jay, a preening clothes horse who'd assumed he'd walk it, was sent home after one of the faintly prickly decision sessions in which parents are obliged to diss each other's children. He sulkily declared himself happy, his mother looked profoundly glum and the other housemates faced the grim prospect of another week living with Nicola – the most aggressive defender of her right to wallow in her own mess until somebody else can be persuaded to clean it up. Come to think of it, Nicola may count as a big enough stick.

That overachievement can have its selfish aspects was demonstrated by the final episode of On Thin Ice, as Ben Fogle and his teammates pressed on to the South Pole – putting in sixteen-hour days as human sled-dogs. James Cracknell was the problem here – competitive to the point of pathology. Despite the fact that his body was falling apart, and despite the fact that coming first was hardly the point anyway, he pushed relentlessly onwards, absorbing the support of his team members like a sponge and reflecting very little of it back. When they found themselves in a crevasse field he refused to harness himself up, storming melodramatically ahead on his own. "The state I'm in, I'm no use to you," he said. The dangerous self-indulgence of this gesture even infuriated the lovably genial Fogle – a far better exemplar of the right stuff, to my mind, because he combines physical determination with a heart that manages to stay warm even at 40 degrees below.

Griff Rhys-Jones has done mountains and Coast has already been bagsied by someone else. So his latest topographical excursion, Rivers with Griff Rhys Jones, takes waterways as the running theme. He started in Scotland, risking his manhood by abseiling down the side of the Grey Mare's Tail waterfall and then subjecting himself to varying degrees of dampness and drenching as he squelched and canoed along the Leven, the Tummel and the Tay. It's calendar television, packed with landscape shots that could be framed and hung on a wall – and Rhys-Jones certainly can't be accused of failing to immerse himself in his subject. He ended by risking his manhood again, swimming a mile in the Tay in November, alongside a wild swimming club whose members appeared to have a lot more natural insulation than he does.