Aristotle did. As Philip Kreager reminded me:
Historians of economics have for some time treated his [Aristotle’s] writings as formative, even though relevant passages in the Politics and Ethics amount to only a few pages.
Wait. There’s more:
In the Politics, however, population is a recurring topic, extensively discussed and integral to the overall argument. “The first part of a state’s equipment,” Aristotle says, “is a body of men, and we must consider both how many they ought to be and with what natural qualities,”
The almost obsessive focus on proportionality I noted in Graunt and Locke is no proof of Graunt’s influence on Locke. The proportional view was central to Aristotle’s Politics and everybody in early modern humanism “up to and including Adam Smith” was doing Aristotle. You didn’t have to read Aristotle. The commentaries on Aristotle were ubiquitous. For Aristotle,
The logic of proportional versus numerical relationships also describes the economy of the household in relation to its size, and this in turn shapes the wider demography of constituent groups. Oikos, the household, is the root of oikonomia, the art of household management, from which we derive the modern term “economics.”
What Graunt did contribute was a brilliant synthesis of humanist Aristotelianism with the techniques of merchant bookkeeping.
Graunt’s work brilliantly synthesized humanist methods of natural history and rhetorical communication that were basic to Aristotelianism with techniques of merchant bookkeeping in which population totals are treated as open or relative accounting balances, rather than closed aggregates; his method arose as a direct response to the need to calculate balances in the body politic.
So no, Graunt didn’t invent economics. He did invent the science of population statistics, though, and thus laid the foundation for modern social sciences. As for Graunt’s contribution relative to Petty’s, Walter Wilcox aptly summed up my own impression, “To the trained reader Graunt writes statistical music; Petty is like a child playing with a new musical toy which occasionally yields a bit of harmony.”