In this commentary on Osiurak and Reynaud's target article, we argue that action is largely missing in their account of the ascendance of human technological culture. We propose that an action-based developmental account can help to bridge the cognitive-sociocultural divide in explanations of the discovery, production, and cultural transmission of human tool use.

We examined the functions of mothers’ speech to infants during two tasks – book-sharing and bead-stringing – in low-income, ethnically diverse families. Mexican, Dominican, and African American mothers and their infants were video-recorded sharing wordless books and toy beads in the home when infants were aged 1;2 and 2;0. Mothers’ utterances were classified into seven categories (labels/descriptions, emotion/state language, attention directives, action directives, prohibitions, questions, and vocal elicitations) which were grouped into three broad language functions: referential language, regulatory language, and vocalization prompts. Mothers’ ethnicity, years of education, years living in the United States, and infant sex and age related to mothers’ language functions. Dominican and Mexican mothers were more likely to use regulatory language than were African American mothers, and African American mothers were more likely to use vocalization prompts than were Latina mothers. Vocalization prompts and referential language increased with mothers’ education and Latina mothers’ years living in the United States. Finally, mothers of boys used more regulatory language than did mothers of girls. Socio-cultural and developmental contexts shape the pragmatics of mothers’ language to infants.

We examined reciprocal associations between early maternal language use and children's language and cognitive development in seventy ethnically diverse, low-income families. Mother–child dyads were videotaped when children were aged 2;0 and 3;0. Video transcripts were analyzed for quantity and lexical diversity of maternal and child language. Child cognitive development was assessed at both ages and child receptive vocabulary was assessed at age 3;0. Maternal language related to children's lexical diversity at each age, and maternal language at age 2;0, was associated with children's receptive vocabulary and cognitive development at age 3;0. Furthermore, children's cognitive development at age 2;0 was associated with maternal language at age 3;0 controlling for maternal language at age 2;0, suggesting bi-directionality in mother–child associations. The quantity and diversity of the language children hear at home has developmental implications for children from low-income households. In addition, children's early cognitive skills further feed into their subsequent language experiences.

Motor development – traditionally studied in WEIRD populations – falls victim to assumptions of universality similar to other domains described by Henrich et al. However, cross-cultural research illustrates the extraordinary diversity that is normal in motor skill acquisition. Indeed, motor development provides an important domain for evaluating cultural challenges to a general behavioral science.