The ability to accumulate solutions and materials found by our predecessors is central to human cognition and social life. The practices that accomplish this not only are built into the intrinsic organization of co-operative action itself, but lead systematically to the progressive unfolding of diversity. Crucially, each reuse of inherited materials occurs within a local activity where it is transformed and adapted to current tasks. As it enters into new relationships of mutual elaboration with the different tools and resources found in each setting it helps constitute the infrastructure that makes tasks possible. Path-dependent transformations lead to the ongoing proliferation of diversity, across centuries, and simultaneously within closely linked settings, including the airport examined in Chapter 16. Lack of copresence might seem to create a crucial analytic divide, and indeed predecessors lack the ability to police their successors’ use of what they created. However, states of copresence, including participants’ access to each other and their task-relevant perception of the environment, are themselves varied and complex. Inherited resources can fall into ruin and disappear if not sustained through ongoing webs of co-operative action.

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