In earlier studies, scientists had offered monkeys mirrors of different sizes and shapes for years, even beginning at a young age, Gong explains. While the monkeys could learn to use the mirrors as tools for observing other objects, they never showed any signs of self-recognition. When researchers marked the monkeys' faces and presented them with mirrors, they didn't touch or examine the spot or show any other self-directed behaviors in front of those mirrors in the way that even a very young person would do.