HOWEVER hard your choirmaster tried, I suspect that, in one aspect at least, your Ash Wednesday performance of the Allegri Miserere was inauthentic: the top lines, surely, were not sung by castrati.

This central phenomenon of late-Baroque music provided the starting point for The Fantastical World of Hormones with Dr John Wass (BBC4, Wednesday of last week). Why should the removal of a boy's testes just before puberty, to ensure that his singing voice never broke, have such widespread other physiological effects as, for example, over-long limbs?

Gradually, medical research showed that many crucial processes in regulating our bodies were governed by chemicals generated in glands, especially the thyroid. Deficiency in such production could be remedied by implanting healthy thyroids from other animals. Experiments proved that the chemicals moved round the body not by "nerves", but by secretion.

More than 80 different hormones have now been identified, and we know that they are created by many different bodily constituents. Even the crucial regulatory part played by the pituitary gland appears to be only part of the full picture; and, more worryingly for those of us who like to cling to the chimera of free will as an essential component of the human condition, it seems that some radical hormonal imbalances are genetically determined: there really is an obesity gene.

Normally, I dislike any programme that contains in its title the name of the presenter; but Professor Wass was so committed to his subject and communicated such a particular excitement about how much it is still in its infancy that the awkwardness is justified.

This contrasted with another BBC4 documentary, The Secret of Bones (Tuesday of last week). The evolutionary biologist Ben Garrod does not have the same antennae to warn him that this or that expression is, frankly, banal. The subject is fascinating: skeletons may seem to be inflexible structures, but he shows us that bones are constantly changing.

It was disappointing, though, to learn that the snake's unique skeleton, consisting entirely of vertebrae, is evolutionary rather than, as I have always insisted, the instantaneous result of divine punishment.

A couple of clergy turned up in Brushing Up On . . . Miniature Britain (BBC4, Thursday of last week), a compilation of TV archive material which last week looked at our national obsession with making models. But the presenter, Danny Baker, wrecked what could have been enjoyable. Each clip of a 1950s enthusiast showing off his model railway, boat, or toy furniture was made the excuse for a lame joke.

There are questions worth asking: why do so many invest huge chunks of their lives in creating small-scale worlds? Why are priests especially drawn to railways? Why, once girls relegate their doll's houses to the attic, is this so predominantly a male pursuit? And however misplaced we might think it, we could at least be impressed by the astonishing levels of skill on display. But Baker's relentless gags degraded the whole subject - and, more seriously, him.