Last night, a new science-fiction drama series called Extant started on television, or rather it started on the video-on-demand service Amazon Prime, which is not quite the same thing.

Television is changing, mutating, evolving and some species are going to get left behind.

Extant itself is promising. It's written by a writer called Mickey Fisher who is pretty much a newcomer to television drama, but it's produced by Steven Spielberg, who is most certainly not a newcomer, and stars Halle Berry in her first television role since the early 1990s.

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In an echo of the recent film Gravity starring Sandra Bullock, Berry plays an astronaut who has just returned from an 18-month solo mission in space. Just as she's trying to readjust to life back on earth, her doctors tell her some shocking news: she's pregnant, even though she's infertile and hasn't been near another human being for more than a year.

What this means is that she's having an alien baby (is there a greetings card for that?), which leaves Berry with a dilemma: has her body been invaded or liberated? She also becomes the target of big-business baddies who think alien/human breeding offers some interesting development opportunities.

Anyone who loves science-fiction, or who wasted their youth on bad films, will know that the idea of an alien baby is hackneyed. As recently as 2012 the movie Prometheus explored the idea in bloody detail, but the idea also cropped up in the 1980s TV series V and the film Inseminoid, which shamelessly exploited teenage boys' fantasies about Judy Geeson.

But it's not the alien baby idea that makes Extant interesting, it's the fact that it's the latest in a growing number of television dramas that are being shown not on traditional channels but through online, video-on-demand services such as Amazon Prime and Netflix.

These are not obscure shows: recently there was House of Cards, the remake of the British drama about a murderous politician that stars Kevin Spacey. And last year there was Orange is the New Black, the glorious, colourful comedy about a women's prison based on the memoirs of Piper Kerman.

All of these shows are part of an attempt by Netflix and Amazon Prime to carve out a new section of the television market because they know that to thrive in TV, showing other people's programmes is not enough . You have to make your own.

So far it's proving successful, but the creation of these new, nimble ideas throws up some tricky challenges for the BBC, the diplodocus of broadcasting. How does it respond without making itself extinct?

The answer is: with difficulty. Speaking at City University in London this week, the BBC's director general Tony Hall suggested the system that ensures half of all BBC programmes are made in-house should end and the Beeb could start making shows for other channels. It's a perfectly fine idea, but the more flexible the BBC tries to be and the more it tries to respond to the changing landscape, the harder it will be to justify its special status - a special status paid for by the licence fee.