II. Economist James Heins said in 2009 that the practice had added $100 billion to the United States economy in the last 30 years. Simon gave away his idea to federal de-regulators and never received any personal profit from his solution. Although not all of Simon's arguments were universally accepted, they contributed to a shift in opinion in the literature on demographic economics from a strongly Malthusian negative view of population growth to a more neutral view. More recent theoretical developments, based on the ideas of the demographic dividend and demographic window, have contributed to another shift, this time away from the debate viewing population growth as either good or bad. Simon wrote a memoir, A Life Against the Grain, which was published by his wife after his death. Wagers with rivals Paul R. Ehrlich – first wager Simon challenged Paul R. Ehrlich to a wager in 1980 over the price of metals a decade later; Simon had been challenging environmental scientists to the bet for some time. Ehrlich, John Harte, and John Holdren selected a basket of five metals that they thought would rise in price with increasing scarcity and depletion. Simon won the bet, with all five metals dropping in price. Supporters of Ehrlich's position suggest that much of this price drop came because of an oil spike driving prices up in 1980 and a recession driving prices down in 1990, pointing out that the price of the basket of metals actually rose from 1950 to 1975. They also suggest that Ehrlich did not consider the prices of these metals to be critical indicators, and that Ehrlich took the bet with great reluctance. On the other hand, Ehrlich selected the metals to be used himself, and at the time of the bet called it an "astonishing offer" that he was accepting "before other greedy people jump in." The total supply in three of these metals (chromium, copper and nickel) increased during this time. Prices also declined for reasons specific to each of the five: The price of tin went down because of an increased use of aluminium, a much more abundant, useful and inexpensive material. Better mining technologies allowed for the discovery of vast nickel lodes, which ended the near monopoly that was enjoyed on the market. Tungsten fell due to the rise of the use of ceramics in cookware. The price of chromium fell due to better