Chance and happenstance: On the Nobel Prize in Chemistry

Only in imagination, the mathematical imagination, does perfect equality exist. A fair coin has an equal probability of heads and tails, so across many tosses, the expectation is for the proportions to approach 50:50. Laborious demonstrations have shown that this is rarely the case; bias is preloaded into life. Only about 10% of humans are naturally left-handed; a species that is a minority can overwhelm a resident population within a few generations. Economists refer to the ‘Matthew effect’ of the rich getting richer and the Pareto principle, and small accretive effects compounding. This is not just human sociology at work. It has been known since the work of the French chemist Louis Pasteur in 1848 that lifeless molecules can have mirror-image forms, like a left-handed glove and a right-handed glove. Chirality is the term chemists use for this molecular “handedness”: a left-handed glove fits the left hand better than the right, even though the two may look like mirror images of one another. Chemists call the resulting predominance of one molecular handedness homochirality, from the Greek words for “same” and “hand”. As with hands, almost all amino acids — the building blocks of proteins — exist as two mirrored variants, but only one of them, the ‘L’ or left-handed version, is found in the proteins in the cells. In the case of sugar molecules, it is the right-handed, or ‘D’, that are part of human DNA. Despite the various available options, life likes to choose one. In their labs, chemists have been able to create equal numbers of left- and right-handed variants of these mirrored molecules, but it turns out that for making pharmaceuticals, it greatly matters which version of a mirrored molecule one uses. The thalidomide drug exists in two mirror-image forms, and their different three-dimensional shapes affect how they interact with biological molecules. Between 1957 and 1961, thalidomide resulted in more than 10,000 babies across the world being born with severe congenital abnormalities.

Henri Kagan and Kenso Soai have been awarded the Nobel Prize in Chemistry for explaining how such homo-chirality may have emerged and devising a reliable method for ensuring that a desired variant of a molecule be synthesised. Kagan’s insight has an intriguing parallel with evolutionary biology: small initial differences need not produce proportionately small outcomes. Soai showed that a tiny initial excess of one molecular form can, under the right conditions, be amplified: the product of his reaction catalyses the formation of more products with the same handedness. Other than laying forth a model of how Matthew effects may underlie evolution, their work underlines how the quest to explain natural phenomena, driven by curiosity alone, can yield insights with practical applications to improve lives and also blaze trails for the future.