Umberto D’Ancona spread Adriatic Sea catch records across his desk at the University of Rome. Ink-smudged columns from Italian fishing ports: Trieste, Venice, Fiume, the city where he’d been born. Fishermen logged their hauls by species. D’Ancona sorted them by year, separating predators from prey, sharks and skates from sardines and mullet. The data covered the decade spanning World War I. During the war, Adriatic fishermen had stayed in port because mines floated in the shipping lanes and warships blocked the routes. Fishing effort collapsed. When peace returned and the boats went back out, D’Ancona found something that defied his training. The proportion of predatory fish in the catch had increased during the war years. Less fishing should have helped all species equally. Instead, the predators had gained ground while their prey lost it. Remove the boats, and the ecosystem didn’t rest. It reorganized.
D’Ancona couldn’t explain it. He brought the data to his fiancée’s father.
Vito Volterra was in his mid-sixties, a mathematician who had spent his career on integral equations and the theory of elasticity. He had never studied fish. He sat with the data for weeks, then published a paper in 1926 that reduced the puzzle to two linked differential equations. The equations showed that predator and prey populations don’t settle into balance. They oscillate. The prey population rises. Predators eat well and multiply. Their numbers swell until they consume prey faster than prey can reproduce. Prey crashes. Predators, now starving, crash behind them, delayed by the time it takes hunger to translate into death. With predators gone, surviving prey breed unchecked. The cycle restarts.
