Much academic work asserts a relationship between the design of a complex system and the manner in which this system evolves over time. In particular, designs which are modular in nature are argued to be more quot;evolvable,quot; in that these designs facilitate making future adaptations, the nature of which do not have to be specified in advance. In essence, modularity creates quot;option valuequot; with respect to new and improved designs, which is particularly important when a system must meet uncertain future demands.Despite the conceptual appeal of this research, empirical work exploring the relationship between modularity and evolution has had limited success. Three major challenges persist: first, it is difficult to measure modularity in a robust and repeatable fashion; second, modularity is a property of individual components, not systems as a whole, hence we must examine these dynamics at the microstructure level; and third, evolution is a temporal phenomenon, in that the conditions at time t affect the nature of the design at time t+1, hence exploring this phenomenon requires longitudinal data.In this paper, we tackle these challenges by analyzing the evolution of a successful commercial software product over its entire lifetime, comprising six major quot;releases.quot; In particular, we develop measures of modularity at the component level, and use these to predict patterns of evolution between successive versions of the design. We find that modularity has a strong and unambiguous impact on design evolution. Specifically, we show that i) tightly-coupled components are quot;harder to kill,quot; in that they have a greater likelihood of survival in subsequent versions of a design; ii) tightly-coupled components are quot;harder to maintain,quot; in that they experience more surprise changes to their dependency relationships that are not associated with new functionality; and iii) tightly-coupled components are quot;harder to augment,quot; in that the mix of new components added in each version is significantly more modular than the legacy design
