Radio has to keep talking, though. Hence it adopts a more contemplative style and focuses more - though not exclusively - on human relationships with animals. Programmes made on this basis can be brilliant (Radio 4's Natural History Programme is regularly compulsive); but it can also make for programmes that seem to forget how extraordinarily interesting animals are for their own sakes, and not because of anything they do to us or we think about them.
That's the trap fallen into by Venom, four programmes described as "a cultural and natural history of venomous animals". It seems a bit mean to put spiders, the subject of the first programme, in this category - they get a bad enough press as it is, and most of them aren't remotely poisonous (12 species out of a total of 34,000 was the figure cited). But the real problem was that the programme was too concerned with the supposed scariness of spiders, and it got hopelessly cluttered by supposedly eerie music and arachnophobe soundbites; consequently, the naked fascination of the spider world was lost.
If Venom allowed nature to be overshadowed by human considerations, The New Sexual Nature, also on Radio 4, makes the opposite mistake. The premise of the series is that you can understand human sexuality through analogy with the animal world - a premise that wears thinner with every episode. Last week's programme, on how we select a mate, ended with Gillian Rice, the GP presenter, rebelling against biological determinism - she married her husband because he had a good sense of humour, not because she thought he would help her to propagate her DNA.
In last night's programme, things got further out of hand: the theme was how animals select the sex of their offspring - coypus, for instance, can spontaneously abort predominantly female litters.
Humans, on the other hand, can't select the sex of their offspring at all, leaving the programme with no perceivable point. If radio series were governed by biological laws, this one would be extinct by now.