The Small Excess

In 1848 a young chemist in Paris sat at a bench with a magnifying glass and a pair of tweezers and did something nobody had thought to do. Louis Pasteur sorted the tiny crystals of a tartaric acid salt into two piles. They were identical in every respect but one: each was the mirror image of the other, as a left glove mirrors a right. Dissolved, one pile twisted polarised light one way and the other twisted it the opposite way. Chemistry had discovered that molecules have hands.

Nature, it turned out, is overwhelmingly one handed. The amino acids in our bodies are left handed. The sugars are right handed. Why life chose one hand rather than an even mixture of both was a question that outlived Pasteur by more than a century. On 7 October the Royal Swedish Academy of Sciences gave the 2026 Nobel Prize in Chemistry to the two men who did most to answer it: Henri Kagan, 95, of Orsay, and Kenso Soai, 76, of the Tokyo University of Science.

The citation speaks of nonlinear effects and autocatalysis in asymmetric organic synthesis. The idea underneath is simpler and stranger. In 1986 Kagan showed that a catalyst need not be pure to produce a strongly one handed product. A modest imbalance at the start could be amplified into a far larger one at the end. Soai went further, finding a reaction whose product speeds its own formation, so that a tiny excess of one hand multiplies itself, round after round, until it swamps the other. For medicine this matters enormously. The thalidomide disaster taught chemists that the two hands of a drug can behave very differently in the body, and the industry now needs reliable ways to make one without the other.

That is the chemistry. The biography is what makes the prize impossible to read as chemistry alone.

Kagan was born in Boulogne-Billancourt in December 1930 to a Jewish family. During the war the family took refuge in a village in the south of France under assumed names. A small boy learned to answer to a name that was not his. A false name is its own kind of mirror image: the same child, reversed, held up to be inspected by anyone who cared to look closely. His survival depended on a village where enough people either helped or chose not to see.

Here the science becomes uncomfortably apt. Most of wartime France was neither heroic nor murderous. It was a mixture, roughly balanced, of the frightened, the indifferent and the opportunistic. What decided outcomes, village by village, was a small excess: the clerk who issued papers, the teacher who asked no questions, the neighbour who kept silent when silence could be fatal. Yad Vashem has recognised more than four thousand French men and women as Righteous Among the Nations. They were never a majority. They did not need to be. Roughly three quarters of the Jews in France survived the war. Kagan’s own discovery says that a small imbalance, amplified, can decide the character of the whole.

The mirror works the other way too. Hatred is also autocatalytic. Each tolerated slur lowers the threshold for the next, and each unpunished attack makes the following one cheaper. France, home to the largest Jewish community in Europe, has seen a sharp rise in antisemitic incidents since October 2023. A society does not need a majority of bigots to become dangerous for Jews. It needs a small excess, left to feed on itself.

Then there is Soai. He was born in Hiroshima in 1950, five years after the bomb, into a city still rebuilding from the war’s most terrible single morning. One laureate was hidden from the machinery the war built; the other was born into the ruins it left. Two children of the same catastrophe, from opposite ends of the earth, now share a prize for explaining how mirror images part company. It is hard to imagine a committee scripting that, and of course it did not.

Israel saw Kagan first. In 2001 the Wolf Foundation awarded its chemistry prize jointly to Kagan, Ryoji Noyori and Barry Sharpless for pioneering work in asymmetric catalysis. Months later Stockholm gave its chemistry prize to Noyori, Sharpless and William Knowles. The Nobel cannot be shared by more than three people, and Kagan was the one left standing outside. French chemists were furious; Nature reported the protest as a cause célèbre. The Wolf Prize has a long record of anticipating Stockholm in chemistry, and on this occasion the Israelis were simply right sooner.

It took a quarter of a century for the Nobel arithmetic to correct itself. Kagan is now the second oldest chemistry laureate in the prize’s history. The Nobel is not awarded posthumously, so the delay was not a formality. Being right early is not the same as being recognised, and recognition that arrives at 95 is recognition that very nearly did not arrive at all. Science, like history, keeps a long ledger, but it does not always keep the people who are owed.

The Wolf Prizes are traditionally presented in the Knesset’s Chagall Hall, beneath the tapestries of Marc Chagall, another Jew who found France both a home and a trap, and who fled it in 1941 for a life he could not have planned. The ceremony ends, the chairs are stacked, the guests go out into the Jerusalem evening, and the room empties.

What the room held, briefly, was a small excess of recognition, the right name read aloud a little before the rest of the world was ready to say it. Twenty five years later the rest of the world caught up. That is how the chemistry works. A little of the right hand, held long enough, decides the whole.