Uncover the hidden ‘sibling action’ that fundamentally shaped modernity. Stefani Engelstein’s groundbreaking work reveals how the concept of the sibling became the bedrock of genealogical classification across European thought. From languages and races to literature and identity, this paradigm organized knowledge and forged collective identities. Explore how this dynamic structure, though destabilizing, influenced fields like life sciences and human sciences, leading to crucial debates on belonging and agency. Essential reading for students and scholars of intellectual history, sociology, and comparative literature seeking a new lens on modern subject formation.