Darwin’s spirit lives on in everything from the Human Genome Project to medicine to conservation biology–the three topics I covered in my post on Friday. It also lives on in brain scans.

While Darwin is best known for The Origin of Species, he also wrote a lot of books in later years, most of which explored some aspect of nature that he showed revealed the workings of evolution. His examples ranged from orchids to peacock tails. In his 1872 book, The Expression of the Emotions in Man and Animals, he proposed that the expressions we humans use–our smiles, our frowns, and so on–are part of a heritage that dates back millions of years, a heritage shared by other mammals. He