n my opinion the WHEEL is one of the greatest innovations of all time as it is the WHEEL that set the whole humanity in motion.
In today's world some of the importance of the wheel has been taken away by modern communications which have made a lot of tasks to be done sitting at home but otherwise the life on this earth would have been much different without this WHEEL.
May be without wheels the whole of humanity would have habitats on the seas because that is the only place where you move without wheels
If you want a great understanding of how innovation happens, and how it borrows, adapts, and expands on other (often unrelated) innovations, check out the fascinating and enjoyable BBC series "Connections" (1978/1979) hosted by James Burke: http://en.wikipedia.org/wiki/Connections_(TV_series). Innovation is not linear, not predictable, and does not follow a "road map".