Language distinguishes us humans; we learn it through experience and social interactions. Especially in the first year of life, human vocalizations change dramatically, becoming more and more language-like. In our closest relatives, non-human primates, language development was previously thought to be largely predetermined and completed within the first few weeks after birth. In a behavioral study now published, researchers from the German Primate Center, the University of Tübingen and the Rockefeller University New York were able to show that the infantile development of vocalizations in common marmosets also includes an extended flexible phase, without which language development in humans would not be possible. The common marmoset is therefore a suitable animal model to better understand the evolution of early infant speech development.