Last night's viewing - Horizon: Playing God, BBC2; 15 Kids and Counting Channel, 4

"Somewhere on this farm there is an animal that is part spider, part something else," said Dr Adam Rutherford in Horizon: Playing God. He said it in a very portentous way, which, along with that title, nudged the mind towards monstrosities and chimeras. "Yikes", you were supposed to think. "A spider and what?" Then Rutherford doubled down just before the reveal: "There's one animal here that I think shouldn't really exist," he said. Did "shouldn't" have an ethical edge to it? Or was it simply a statement about likelihood? The answer to that was for later, though, because first we had to look upon the beast itself. I think more excitable viewers may have been a little disappointed by what eventually turned up. If a fairground barker promised you a spider-goat, after all, you'd expect nothing less than a few extra legs, even if you didn't insist on the full eight. You'd want fangs, or bulging red eyes. If you just got a goat you might ask for your money back. The truth, though, was a bit less exciting than the promise. When Rutherford said "part spider, part something else", our minds naturally conjure up a half-and-half deal. What you actually got was something that blended a microscopically tiny bit of spider with an overwhelming quantity of goat, making a transgenic animal that could produce spider web proteins in its milk.

Interesting enough without the hoopla, I would have thought. But whereas it used to be the case that science presenters were required to radiate an authoritative superiority of knowledge, they now have to pretend to be small boys for at least part of the time, gushing and goshing as if they've just started work that day. This can easily become absurd: "You can actually see the milk coming out!" gasped Rutherford as he watched a spider-goat being milked, as if lactation itself was a recent discovery. "I don't know what these animals think about being spider-goats," he continued, "or whether they've got any idea at all." Perhaps he should apply for a research grant into this promising field of study.

The content itself, once he got to it, was genuinely interesting: the boom in synthetic biology, which deals with how new organisms can be synthesised out of mail-order parts. Essentially we've worked out how to hack the operating systems of living things, tweaking the DNA code so that a yeast cell excretes diesel fuel instead of alcohol, or an E.coli bug fluoresces under ultra-violet light. And this new technology is advancing so fast that it brings with it the inevitable anxieties that attend all new technologies. I'm glad to say that God wasn't discussed at all here – beyond the title – because it's difficult to see why this adjustment of our environment is really any different in moral terms than artificially making fire or brewing alcohol, both of which have their downsides too. There's no question that this ability requires some more thought about that tricky borderline between the possible and the permissible, but since we made the problem we're probably best placed to solve it too.

God was invoked by Tania and Mike Sullivan in 15 Kids and Counting. As devout Catholics they've left it up to Him to decide how many children they have, because they think that contraception is sinful. God seems to have had some difficulty making up his mind, because Tania's had eight miscarriages so far, as well as 11 healthy children. Also featured in the programme were the Radfords from Morecambe, who didn't outsource the responsibility for their vast brood to a deity but speculated that their addiction (their word) to procreation might have something to do with the fact that they'd both been given up for adoption. Both families seemed pretty happy, it has to be said, and neither mother looked remotely ready to stop. "Never say never," said Mrs Radford, which may explain how she'd ended up with 15 children.