It has been estimated that throughout prehistory, the world average GDP per capita was about $158 per annum (adjusted to 2013 dollars), and did not rise much until the Industrial Revolution. The first object or physical thing specifically used in a way similar enough to the modern definition of money, i.e. in exchange, was (probably) cattle. The first economist (at least from within opinion generated by the evidence of extant writings) is considered to be Hesiod, by the fact of his having written on the fundamental subject of the scarcity of resources, in Works and Days.