China yesterday threw down a challenge to America's 50-year dominance of the global economy as it proposed replacing the dollar as the world's main reserve currency with a new global system under the control of the International Monetary Fund. In a muscle-flexing move that will be seen as an attempt to exploit the big shifts in economic power created by the recession sweeping the West, Beijing said that the dollar's role could eventually be taken over by the IMF's so-called Special Drawing Right (SDR), a quasi-currency that was created in 1969.