Imagine a football field in which the distance from the visiting team’s goal line to the last four-fifths of an inch prior to the home team’s goal line represents human existence prior to the industrial revolution. Or, to invoke a structural metaphor, imagine a large multistory Victorian style house in which the foundation, the framing, the floors, the walls, the fixtures, the insulation, and the original siding represent the evolutionary history of our species up to the onset of domestication just prior to the agricultural revolution. The remainder of our species’ history would be equivalent to a layer of vinyl siding tacked over the top, with mass technology represented by a thin veneer of paint over the top of that. The siding plays no role in the structural integrity of the house—and even less so, the paint.
But four-fifths of an inch can mean the difference between a touchdown and losing the game entirely!