Nathan Pearson is a geneticist at Knome, Inc., where he and his colleagues build simple, engaging tools that compare one whole human genome to the next, in order to cast new light on human health and history. Fascinated by human genetic diversity since working as a young student in the laboratory of Luca Cavalli-Sforza (Stanford University), he traveled with Spencer Wells (now head of the Genographic Project) to collect DNA from people living throughout Eurasia, to reveal traces of ancient migrations recorded in their genomes. In doctoral work at the University of Chicago, he studied patterns of sequence variation on the great ape sex chromosomes, spotlighting how mutation, recombination, and natural selection have jointly made the X and Y ever more different from each other. Later, in post-doctoral work at the University of Michigan, he first delved into the emerging world of high-throughput sequencing, grasping its power to address important open questions in biology. Today, working with a talented team of scientists and programmers, he helps researchers and consumers sift through the billions of letters in each human genome, and understand which important spellings make each person unique.