An interesting paper by a group of researchers from the Max Planck Institute for Evolutionary Anthropology has appeared in the latest edition of the journal Science. The researchers have taken an interesting approach to investigating the differences between humans and chimps - they have used a relatively new genetic tool known as microarray analysis to examine the differences in gene expression between the chimps and humans. Their results are interesting for two different reasons. First, it is always interesting to learn more about the differences that separate us from our nearest relatives. Second, this paper has actually used the human-chimp relationship as a model system to investigate some basic evolutionary questions.