Why is life chiral?

Why life is chiral has puzzled scientists for well over a century. Louis Pasteur famously discovered molecular chirality in his meticulous experiments in 1848. He separated by hand the mirror-image forms of salts of tartaric acid and saw that their solutions will rotate the plane of polarised light in opposite directions. ‘There is no doubt,’ he wrote in 1860, ‘that there is a grouping of the atoms [in tartrate ions] of an asymmetric type that is not superposable on its mirror image.’

Pasteur convinced himself that this property of molecular chirality was a barrier separating the living from the inanimate worlds – almost an echo of the vitalistic belief in the specialness of organic nature that Pasteur’s work on microbes and ‘spontaneous generation’ helped to dispel. He set out to find the origin of this handedness of life’s molecules.