Records from two nearly 100-year-old shipwrecks, the Titanic and the Lusitania, have given researchers new insight into human selfishness — and altruism.

On one boat, it seems, the men thought only of themselves; on the other, they were more likely to help women and children. This occurred for one key reason, researchers said: time. The Lusitania sank in about 18 minutes, while the Titanic took nearly three hours. Women and children fared much better on the Titanic.

“When you have to react very, very fast, human instincts are much faster than internalized social norms,” said Benno Torgler, an economics professor at Queensland University of Technology in Brisbane, Australia, and one of the authors of the study, published in the current issue of Proceedings of the National Academy of Sciences.

“It’s very nice to get a nice and controlled experiment,” he said. “You’re in the ship; you cannot go in and out. We were looking for shipwrecks that were very similar — similar structure, similar rates of survival, only a couple of years apart.”