People are very different from one another and yet they are so similar. The concept of human diversity is relative — diverse as compared to what? A good comparison may be to chimpanzees. According to Sarah Tishkoff, an associate professor at the University of Pennsylvania School of Medicine, chimpanzees are roughly three times as diverse as humans. "People are often surprised by that because there's a lot more modern humans around than there are chimps. But it means that in the past, chimps had a larger population size than humans," she says.