that probably holds for the two of us. >> charlie: this is charles darwin's book, the expression of the emotions in man and animals. darwin was amazing. >> amazing man. he was without a doubt the most important biologist who ever lived. he not only formulated the theory of evolution but he realized that behavior evolved. just like body parts evolve, so does behavior evolve. you can see examples of human behavior in simpler animals. and since emotion is an important feature of behavior, you can see expressions of emotion in animals and you could detect that. he looked around at different groups of people living throughout the world and he realized that they all had a fixed number facial expressions. six or seven that expressed different emotions. and those are conserved. so whether you're living in the orient or living in america, you express emotions in exactly the same way through the same facial expressions. >> charlie: this is an extraordinary idea and we explore the social brain with our group of experts. understanding how this remarkable idea takes place in our brain. >> most anima