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Last Night's TV - Horizon: Are We Still Evolving?, BBC2; Leah's Dream, ITV1

Bedazzled by a brave new world

We're all doomed, according to Horizon. It's said this sort of thing before, of course, and frankly you'd have slit your wrists by now if you'd taken all of its previous prognostications to heart. It went through a dizzily apocalyptic phase a while ago, apparently convinced that what the public really wanted from a serious science strand was a thinly disguised disaster movie. But – although the dark sky lens filter and the sepulchral music got a heavy workout in Alice Roberts's film about human evolution – this was a far more thoughtful "we're all doomed" than usual, and it provided a wryly teasing conclusion to the programme, not a banner headline to pull in the rubes.

We're doomed in the very long run, incidentally, not imminently threatened by rogue meteors or a mutating virus (though the latter did play a part in this story), but destined, eventually, to give way to our evolutionary heirs. That was the point of the programme – that far from having escaped the iron grip of evolutionary change we're still subject to its laws, and may even have accelerated its rate of change. This goes against the grain of common-sense assumption, which is that evolutionary change should be too slow to be easily detectable in recent human history and that, in any case, technology has lifted us free of an animal subjection to selective pressures.

Neither assumption is necessarily true, though. Dr Alice, in a derelict Devon copper mine, went hunting for worms that have successfully adapted to toxic soil conditions in just over a century. They are, the worm expert said, now more genetically distinct from regular earthworms than we are from mice, though you'd have to say that they've hidden the fact pretty well. And, although we're considerably more complicated than earthworms, research in Nepal has revealed that Sherpas are now physiologically different to the rest of us in ways that go beyond the superficialities of outward appearance. If you or I set off to climb Everest, we cope with the lack of oxygen by temporary bulking up our haemoglobin, which works but can cause other problems. Sherpas have evolved extra-curly capillaries to do the job instead.

Equally intriguingly (and, obviously, once you think about it a little bit), while human technology exempts us from some evolutionary pressures it also creates entirely new ones of its own. For our ancestors the ability to digest lactose in adulthood wasn't all that common, but the development of farming, and the huge advantage conferred on those who could take advantage of cow's milk ensured that the variation spread in the population. You can now map its prevalence, showing how neatly it corresponds with societies in which dairy farming was culturally central. More balefully, intensive chicken farming may have been implicated in the transformation of a mild poultry disease into an absolutely lethal one, a reminder that we can't be sure that our actions won't create the kind of environmental challenge we'd be hard pressed to overcome. Modern cities are a lot more like battery farms than a free-range paddock, and should a virus evolve that can get past existing medicines then natural selection will return and bite us to the bone. The last place to which Dr Alice took her slightly unnerving permanent smile was an LA fertility lab where the technology exists to offer parents a selective menu of traits for their next baby (though at present you don't get to choose anything but gender) – another twist to the story. I don't know whether it's my imagination, by the way, but Horizon itself seems to have undergone an evolutionary advance recently, from a palaeolithic concentration on audience figures to something more cerebral. I'm pretty sure that the brow has lifted an inch or two and the posture is a tad more upright. These days you could easily mistake it for Homo sapiens.

Leah's Dream showed you how cruel genetic mutations can be when they twist in the wrong direction – observing the slow, inexorable regression of a young girl with Niemann-Pick disease, which induces a premature senility and generally kills off its victims before they reach the age of eight. Leah had beaten the odds in one sense – since she was shown here celebrating her ninth birthday – but it was also clear that it was only a postponement not a permanent victory. Filmed over two years, Chris Malone's film was able to capture the way that Leah's abilities slowly faded, an agony for her mother, who had survived a serious cancer herself and the collapse of her marriage.

It was, rather self-consciously, a study in maternal love and human fortitude and it didn't always avoid falling into tabloid sentimentality. There was a real-life justification for adding Abba's "I Have a Dream" over the final sequence of the film, but it would have been better, in my view, not to have taken advantage of it. The narration also occasionally seemed to wheedle for your emotions, rather than letting the facts speak for themselves, which they would have done perfectly eloquently. Perhaps the most poignant detail was the persistence of parental hopes in the face of the disease's inversion of the natural order. "I want her to remember me as being happy mummy, not sad mummy," said Leah's mother, Lindsey, although the sad truth was that Leah's memory was fraying with every passing day, and that in any case it wouldn't be long before Lindsey was remembering Leah rather than the other way round.