I was not aware of Miriam O'Reilly, the former presenter of Countryfile, until she became a martyr for women over 50. O'Reilly claims that Jay Hunt, the former controller of BBC 1, dumped her because her face could not survive the age of high-definition television. It is perfectly possible, however, that Hunt took against O'Reilly for individual rather than general ageist reasons. Plausibly, it is not that Hunt "hates women", as a fellow female presenter alleged, but that she didn't rate her.

Jay Hunt has told the employment tribunal that the charges against her were untrue, distressing and "offensive on every level". She declared: "The last thing I would ever do is discriminate on the basis of gender or age." But it is her job to make casting judgements. The series producer Teresa Bogan was straightforward about this, calling the replacement presenter, Jackie Brambles, "pretty".

Meanwhile, a radio producer called Lucy Lunt has made a distinction that will have other women examining their work wardrobe: O'Reilly was "a little black dress" presenter, she told the tribunal, whereas the show needed more "red carpet frock".

Television presenting is a type of performance. Nobody complains when some perfectly able actress is thrown aside for a bigger name when the show transfers or is made into a film. In any forum where your face is on show, it matters how you look and your looks can go out of fashion. Hunt, right, understands the need to hold on to viewers, as she demonstrated last week by wearing a succession of tribunal coats.

Appearing on television makes you go mad, driven by the need to stay on screen. Look at Christine Bleakley's desperation as her ratings plummet. Many committed presenters have vanished from the screen, not culled, so far as I know, but because of capricious public taste.

The excitement about this story is that it is women vs women. Hunt has been far more scrutinised in her former job than a man would have been. She is generally a thoughtful, talented boss and I'm sorry to see her leave the BBC for Channel 4.

The case has uncovered a cultural and social change. Jay Hunt was making a legitimate professional judgement about Miriam O'Reilly. Hunt's job was to reflect public taste. But what she and all her colleagues misjudged was the public's altering perceptions of older women. Hunt reflected public taste, but did not lead it. The "mix" is at the heart of BBC programming – gender, race, politics. Rachel Johnson claimed last week that television had an unacknowledged policy of contrasting blondes with brunettes.

It is the further subdivisions that defeat the BBC. Women have advanced, but society is perplexed by women past childbearing age. In America, they retain power; in France glamour; in Britain they disappear.

It takes time to readjust, and television has been especially slow. Hollywood once discriminated against older women. Now our most famous British actresses are Helen Mirren and Judi Dench. Jay Hunt's professional fault is not lack of feminist empathy, but missing a social trend.

Sarah Sands is deputy editor of the London Evening Standard