Anthropological contributions are essential to understanding the evolution of writing and its potential variation. Although Stanislas Dehaene calls for a 'neuro-anthropological perspective', he neglects anthropological evidence, including the only indisputable case of independent invention of writing: the pre-Columbian systems of the Americas. Here I argue that anthropological and historical accounts of the cultural evolution of language suggest that ecological, technological, social and political factors have all influenced the ongoing development of writing systems, even in directions contrary to that predicted by a model of increased neural efficiency. In addition, Pre-Columbian writing systems, not subject to a diffusionist confound because of their independent invention, caution that our research on diversity in writing may represent a small, systematically biased sample. To truly understand neuro-cognitive variation, we have to avoid both overly ambitious universalisms and radical cultural relativism.