The past few years have led to the widespread recognition that morphology is an independent domain of language functioning in dynamic interdependence with more familiar domains such as phonology and syntax. This has permitted nuanced research into the organization of morphological systems as well as the development of hypotheses concerning factors responsible for such organization. In this chapter we compare two classes of hypotheses — adaptive explanations and neutral ones — for attested differences in morphological complexity claimed to correspond with sociocultural and demographic factors. While both examine language change as a (cultural) evolutionary process, we argue that much recent work on adaptive hypotheses for morphological complexity has been uncritically adaptationist, neglecting key results and lessons from population genetics about how to study evolutionary systems. Finally, we argue that neutral explanations are presently more likely explanations for the apparent association of morphological complexity and smaller, historically more isolated populations and should a priori be preferred over adaptive explanations unless and until a high evidential burden has been met.