The Weekend's TV: Who Do You Think You Are? Sun, BBC1<br/>Richard Hammond's Engineering Connections, Sun, BBC2

When drama runs in the family

Sarah Jessica Parker' (Getty Images)

The underlying story of Who Do You Think You Are? – the first of the American series of Wall to Wall's blood-and-roots hit – was of the slow convergence between Sarah Jessica Parker's noisy incredulity and a revelation that actually seemed worthy of it.

You can take it as read that American versions of British reality shows will be brasher and louder than the originals, because American television executives always like to take the type-size up a point or 10, just in case someone misses the message. If Gordon Ramsay shouts a bit and loses his temper over here, then he'll have to turn into a borderline psychopath in America, so that nobody can be in any doubt that him being angry and shouty is what the show's "about". If the spouse-traders in Wife Swap here get a bit testy with each other during the debriefing, then over there they'll virtually haul out handguns. That standard inflation rate – combined with the fact that any immigrant nation brings a certain febrile intensity to questions of origin – meant it was sensible to be braced for a bit of gush from the start. Even so, Parker's wide-eyed excitement was... well, let's say, not entirely British.

"Oh. My. God!" she exclaimed when her mother brought out an old snapshot of her maternal great grandmother, "Wow!" It was as if she was stunned to discover that her family hadn't been produced by spontaneous generation only a few years previously. And each successive generational onion-skin only amplified the thrill. It was, she thought, "unbelievable" that a 19th-century ancestor turned out to be called John Eber Hodge and hailed from Cincinnati, even though that was the town where she grew up. And when the local records revealed that he'd headed west as a forty-niner, hoping to strike it rich in the California gold fields, she had to break the word in three to convey the full scale of her astonishment. "Un. Bee. Leevable," she said.

We were getting a little closer to a match between stimulus and reaction here, even if it was surprising to find that she was surprised by remains of worked-out goldmines in the Californian hills: "I just cannot believe that this is part of that," she said. "That it's still here... that nobody's moved it." And then her almost limitless capacity for startlement finally encountered a worthy object. Travelling to New England to trace back the Hodge line, she was first of all delighted to discover that her American roots went back to within 30 years of the Mayflower ("this is soooo crazy") and then virtually rendered unconscious by the revelation that a female ancestor had been named on a warrant during the Salem witch trials. At last, a match! We'll give you that one Sarah Jessica, since I think pretty much anyone would get a bit giddy on finding out that a distant relative had played a dangerously direct role in one of America's darker episodes. "I just want to go on record that I'm finding this physically upsetting," said Parker, as she read the deposition of one of the hysterical teenagers who sustained the witch hunts, to the effect that Esther Elwell had murdered her neighbour in phantasmal form. Esther was very lucky in her timing – her accusation came just as the trials began to collapse in on themselves, and she lived on to the age of 82. "It's changed everything about who I thought I was," said Parker about this discovery. "I have real stock in this country, real roots.... you know, I'm an American, I'm actually an American!" That's right, Sarah. We've Bee Leeved it for years and now you can too.

I wouldn't mind seeing a genealogical tree for Richard Hammond's Engineering Connections, in which the little meerkatty one off Top Gear unveils the unexpected continuity between current engineering marvels and ancient techniques. I'm seeing something around the eyes that reminds me very much of a Seventies series called Connections, in which James Burke created a kind of historical domino race, with one historical innovation tipping off the next one, concluding in some modern marvel that appeared to have absolutely nothing to do with where we began. Whereas Burke was all about unexpected consequences, though Richard Hammond's Engineering Connections is more generalised boy's fun, often involving practical experiments in which something is broken or blown up. Last night's episode – focused on the construction of Hong Kong's new airport – included a section on Barnes Wallis's development of lattice-steel structures for the Wellington bomber and permitted Hammond to play with a crane and iron girders. A later sequence, about the flexible joints that prevent the airport roof taking off for Thailand when a typhoon strikes, gave him the excuse to destroy a car, while the explanation of the Doppler effect involved a radio-controlled plane buzzing the film crew in a way that will surely have required an extra sheet on the risk-assessment form.

It's all pretty harmless, even if Hammond's larky manner and pretended "oo-er" moments get a bit wearing after a while. And it does do something to shine a light on engineers, people who don't always get quite enough credit for the fact that we can go about our business without the roof falling in on us. It did seem a little odd though that neither last week's programme – about the Millau Viaduct in France – nor this one bothered to give a namecheck to the architect of both schemes, Norman Foster. I know it's bolts and maths that keep these things up, but the fact that they're beautiful too isn't just an accident.

t.sutcliffe@independent.co.uk