Well, for what it's worth Wikipedia article on the paleolithic suggests there is much evidence of trade during that era (referenced, but I don't have the time t

Well, for what it's worth Wikipedia article on the paleolithic suggests there is much evidence of trade during that era (referenced, but I don't have the time to research that ATM). But that's beside the point really. The issue here is how we define what economy is and what trade is. But more to the point, trade in general is not a defining characteristic of capitalism, it's not the differentia specifica of capitalism. But I agree that the statement "trade is the foundation of any economy" is too strong in the sense that it's not only trade that is needed to have an economy (you need production, consumption, etc.).