Darwin's Garden, by Michael Boulter

Charles Darwin's house to the south-east of London at Downe, enfolded in English countryside despite being caught within the cordon of the M25, will not officially become a World Heritage Site in time for next year's double anniversary: 200 years since Darwin's birth, 150 since the publication of the Origin of Species. Its bid for listing was withdrawn after a sniffy report from a panel that advises Unesco's committee, opining that Down House and its surroundings are not of "outstanding universal value".

It is hardly surprising that the list of sites barely registers science as part of the world's heritage. Down House was not just a rural retreat where Darwin could write up his notes. It was a place that nurtured his thought; whose grounds were the site of experiment and contemplation. Visitors can pace out the Sandwalk at the bottom of the garden that was his daily "thinking path"; they can gaze out across the same fields and walk among the descendants of the living forms that surrounded him as he strove to understand the variety of life.

Above all, it was the place where he developed a universal theory about the means by which living forms develop, and the relationships between them. Perhaps that is the problem. People still don't like to be told that natural selection is how life works. For 150 years, commentators have devalued or ignored the idea. By the late 19th century, they had achieved the "eclipse of Darwinism", during which the fact of evolution was accepted, but not the mechanism.

Michael Boulter, a biologist who admitted in a previous book that he had trouble understanding natural selection, is part of this tradition. Unfortunately, he also struggles to present an alternative vision of a more rounded biology. When this book dwells on life at Down House, it is brightened by the recollections of Charles and various relatives. The further it ventures out of the garden, into the development of evolutionary thought, the more it is likely to mystify or mislead.

Typical is a passage suggesting that the First World War and the Vienna Circle of positivist philosophy together inhibited the study of natural selection by promoting physics and reductionism at the expense of biology. This contention seems rooted in a facile opposition between "hardline" scientists and softer, fuzzier ones. But the study of natural selection was transformed, and its power recognised, by scientists who analysed it mathematically in the 1920s. Boulter fails to convey the point, locates one of the investigators, Ronald Fisher, in the wrong continent, and implies the other, JBS Haldane, had no time for "myth", though his immense head was full of it. The muddle pervades all levels, from abstract ideas to factual detail. It's a pity, because Darwin's garden is such an exquisite site for a book.

In trying to achieve a harmony between the productivity of reason, family life, and the humble appreciation of the natural world, we might all do worse than to see how Darwin cultivated his garden.

Marek Kohn's 'A Reason for Everything' is published by Faber & Faber