Lynne Truss leaps the species barrier and appreciates some clever monkey business in a highly-evolved novel of ideas; Ark Baby by Liz Jensen Bloomsbury, pounds 15.99
There's a game you can sometimes play with ambitious fiction writers: reconstruct the reference library they gathered round them while their novels were taking shape. Liz Jensen's impressive second novel Ark Baby is the sort of book this game was invented for. Wilfrid Blunt's The Ark in the Park is a candidate, the biologist Steve Jones is a certainty; while Peter Carey's Oscar and Lucinda can't really be denied. Will Self's recent Great Apes? Well, that came out too late (and anyway, who cares?). But what about John Collier's 1930 novel His Monkey Wife? Ark Baby is a rich, original book which augments its appeal by reminding you of at least a dozen others.

It's a double narrative: two protagonists tell their stories, 150 years apart. In the year 2005, we have Bobby Sullivan, a cynical vet who thinks nothing of killing a pet monkey for dosh. He lives in very peculiar times. A fertility crisis presages the extinction of the British; an Egg Bank is sabotaged, monkeys are adopted as surrogate children; the demarcation lines of the human species are becoming unacceptably blurred.

Meanwhile, back in the 1860s, the deformed and hairy foundling Tobias Phelps grows up in a vicarage in Northumberland - a place of wind and flood, where men pull thistles for fun; the Old Testament is regarded as namby-pamby; and the new orthodoxy of Darwinism is cursed as an abomination.

Ark Baby is a clever, beautifully written, zeitgeisty novel about man's uncertain place in the great chain of being. What are the origins of Tobias? Do they have any connection with the so-called "Ark" - a converted slave ship whose cargo of stuffable animal specimens arrived dead and stinking in London?

The illiterate testimony of a woman caged on board the Ark among the beasts reminds us of a world of captivity, creaking boards, and frightened animals. Tobias has memories of a gilded cage, and toes like thumbs...

In the best sense of the word, the book is fanciful. And being fanciful, it is entertaining, even if its humour is not always the sort to make you laugh aloud. Light relief is provided by the household of Sir Ivanhoe Scrapie, chief taxidermist to the Palace, whose opium-addicted wife succumbs from eating the poisoned flesh of a Gentleman Monkey.

After death Mrs Scrapie hovers between the two narratives, inhabiting both, and informing her daughter Violet that the future contains such marvels as long-life milk. Nobody cares for her company very much in either time scheme, but from the reader's point of view, she's a riot.

Given that determinism is her principal theme, and that no clues are withheld from the reader, it is miraculous that Jensen still contrives to surprise us with the conclusion of the story. True, the characterisation is weaker in the modern strand. But if they gave prizes to authors for keeping a cool head under potential thematic overload - well, you have to hand it to someone who can juggle this lot.