This image is yet another representation of ‘family trees’ of languages, a common way of illustrating relationships among the numerous languages spoken by humans. But what are the roots of human language? Why did humans develop these complex forms of communication when other species did not? An article by Paul Ibbotson, a developmental psychologist, and Michael Tomasello, co-director of the Max Planck Institute for Evolutionary Anthropology, argues that language developed from the human need to collaborate. What do you think?