What significant purpose has wood been used for as long as humans have built shelters?
Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction. Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).
The development of writing enabled knowledge to be stored and communicated across generations with much greater fidelity. Combined with the development of agriculture, which allowed for a surplus of food, it became possible for early civilizations to develop, because more time and effort could be devoted to tasks (other than food production) than hunter-gatherers or early subsistence farmers had available. This surplus allowed a community to support individuals who did things other than work towards bare survival. These other tasks included systematic studies of nature, study of written information gathered and recorded by others, and often of adding to that body of information.