Science under Adversity argues that the Global South served as a dynamic arena of scientific innovation, circulation, and international collaboration. In this richly detailed history of the development of Latin American physiology in the early- to mid-twentieth century, Marcos Cueto shows that productive tensions between doctors and scientists in Argentina, Mexico, and Peru and their counterparts at US research centers and philanthropies shaped the life sciences in the region. Latin American physiologists took part in networks of scientific power that dictated distinctive styles of laboratory research and strategies. By tracing the trajectories, challenges, and overlooked figures who shaped these developments, the book highlights the crucial role of the global circulation of academic science in consolidating the modern life sciences-and reveals how Latin American researchers confronted asymmetries while redefining what it meant to be modern, universal, and simultaneously rooted in local realities. In doing so, it contributes to broader historiographical debates on the geopolitics of knowledge, demonstrating that scientific modernity itself was shaped through unequal yet mutually constitutive exchanges.