Scottish economist Adam Smith's The Wealth of Nations heralded – or caused – the market-based economic system that has increasingly become the norm since the book's publication in 1776. Some say that Smith's magnum opus was to economics as Newton's Principia Mathematica was to physics or as Darwin's On the Origin of Species was for biology. Certainly the book made its impact in the early United States. 1776 predates wide usage of the term capitalism, now commonly associated with Smith, and which Smith refers to as a "system of natural liberty." Smith presented what we today consider Economics 101: supply and demand, and the importance of specialization and the division of labor. He also posited that individuals pursuing their own self-interest could unintentionally create a more just society by so doing – an idea sometimes referred to as the "Invisible Hand." Even Smith's critics do not deny the book's immense influence. Murray Rothbard levels the criticism that The Wealth of Nations, in fact, eclipsed public knowledge of all economists – better ones, he says – before Smith.