In this paper, we explore the heuristic potential of a set of ideas about the structural and functional complexity of systems, proposed in the 1990s by theoretical biologist Daniel McShea. In particular, we focus on the structural aspects of the complexity exhibited by social systems organized into low- and intermediate-level functional units (i.e., groups and teams). To address this subject, we describe a methodology suited for measuring the complexity in the organization of work in such systems, which is primarily based on hierarchical task analysis. With this methodology, we approach a concrete case study: the construction of megalithic monuments in late prehistoric Iberia (ca. 3800–1800 BC). On the basis of the analysis of the three best documented, most structurally, and functionally complex monuments built within each of the three periods under study (Late Neolithic, Copper Age, and Early Bronze Age), we found that there was a trend towards less complexity in work organization related to monument building from the Late Neolithic to the Early Bronze Age. We discuss the importance of these results in light of the existing models of social complexity in European Later Prehistory, concluding that a more balanced view of social processes would be obtained if we look at complexity as a property of every different social system integrated into the whole society, and not as an exclusive property of the latter.Facultad de Ciencias Naturales y Museo