Most stock market trades are made by algorithms, not humans, and they've already caused crashes. We need to understand their group behaviour to avoid disaster

Gone to lunch, or just gone? Qilai Shen/Panos

ROBOTS are taking over Wall Street. “Technology has utterly transformed the financial system,” says Andrew Lo, an economist at the Massachusetts Institute of Technology. “The vast majority of day-to-day trading is done purely algorithmically.”

More and more human traders are being shown the door. And researchers like Lo are beginning to find that the more the stock market is run by machines, the less it behaves like one. Today’s markets are an ecosystem, a zoo of bots grazing on our pensions and investments – and no one quite knows how they work.

Is …