Most scientists are aware that developmental databases derive primarily from Western, middle-class samples, but fewer are cognizant that developmental theories can be similarly biased. There is urgency in revising developmental theories, both scientifically (embracing diversity is essential to the study of human psychology) and applied (it is damaging to apply WEIRD standards/methods/theories to evaluate development in the multitude of non-WEIRD contexts).

We evaluate the extent to which two prominent developmental theories are inclusive. We find that Shared Intentionality Theory is based on a WEIRD bias in the foundational databases: the core constructs lack culturally diverse data, undermining claims that this theory explains human-general social cognition. In Attachment Theory, we illuminate the lack of inclusivity in the core assumptions and resulting claims of the meaning and measure of the attachment system: this theory excludes cultural diversity in social-emotional constructs focused on communal orientations (e.g., interdependence, attachment networks) found in many people of the Global South, and neglects culture-specific adaptive behavior patterns.

Acknowledging the lack of inclusivity at the level of theory is necessary. We urge researchers to take a more WILD approach: obtain Worldwide samples, study development In situ, focus on Local cultural practices and ethnotheories, and consider development as Diverse. Being WILD entails attending to inclusivity during the entire research process, from framing the research questions to interpreting the data (e.g., respecting all adaptive behaviors in development). Five Steps for Increasing Inclusivity can be used as a practical guide to decenter psychological theories from their current WEIRD mindset.