Broadly true. Peer-reviewed reviews describe humans as an obligatorily group-living species with a basic need for inclusion and differentiation, and they find robust in-group favoritism that can even appear from arbitrary group assignments across societies. At the same time, the literature also emphasizes that people have multiple, overlapping identities and that intergroup behavior is context-dependent, so “tribal” is a useful shorthand rather than a complete description of human nature. (sciencedirect.com) Sources: Geoffrey J. Leonardelli, Cynthia L. Pickett, and Marilynn B. Brewer, “Optimal Distinctiveness Theory: A Framework for Social Identity, Social Cognition, and Intergroup Relations” (Elsevier/ScienceDirect); Alexandra et al., “Is in-group bias culture-dependent? A meta-analysis across 18 societies” (Springer); Aino Saarinen et al., “Neural basis of in-group bias and prejudices: A systematic meta-analysis” (Elsevier/ScienceDirect); Sonia K. Kang and Galen V. Bodenhausen, “Multiple Identities in Social Perception and Interaction: Challenges and Opportunities” (Annual Reviews).