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A RIDDLE buried deep within Charles Darwin’s On the Origin of Species has been solved almost 150 years after the book was first published.

Within his ground-breaking treatise, Darwin cryptically refers to what has been described as the world’s first ecological experiment. In a short passage, he describes horticultural trials showing that the productivity of a plant community increases as it becomes more diverse.

But details of the experiments have remained a mystery. Now biologists Andy Hector at Imperial College in London, UK, and Rowan Hooper, based at the National Institute for Environmental Studies in Tsukuba, Japan, have unearthed a document in the British Library’s rare manuscript collection that reveals all. The trials were run at Woburn Abbey in south-east England by George Sinclair, head gardener to the sixth Duke of Bedford. But the experiments were on such a large scale they were probably ordered by the Duke himself.

The manuscript describes 242 plots of pasture species such as grasses and clovers. Sinclair compared how well various mixtures grew on different soil types. The aim was partly practical, to work out how best to grow pasture for grazing. But Hector believes Sinclair and his employer were also interested in deeper questions, such as where diversity comes from, and how it is maintained. “These are probably the central questions in ecology even today,” says Hector.

The mystery started because Darwin originally intended that Origin, published in 1859, would only be an abstract of a larger work on his theory. As such, it did not include references.

But ecology historian Sharon Kingsland of Johns Hopkins University in Baltimore, Maryland, says it is impossible to define Sinclair’s work as the first “ecological experiment”. You cannot apply modern concepts to the work of past scientists, she says. If anything, the credit should go to Darwin for putting the work in a theoretical context.