The source of . . . improvements in productivity is the human mind, and a human mind is seldom found apart from a human body. And because improvements – their invention and their adoption – come from people, the amount of improvement plainly depends on the number of people available to use their minds.
The connections between numbers of scientists, inventors, and ideas, and the adoption and use of new discoveries are difficult to delineate clearly. But the links needed to confirm this effect seem very obvious and strong. For example, the data show clearly that the bigger the population of a country, the greater the number of scientists and the larger the amount of scientific knowledge produced; more specifically . . . scientific output is proportional to population size, in countries at the same level of income.
. . . The main contribution that additional persons make to society is the new knowledge of all kinds – scientific, organizational, and everyday knowledge. . . that they create and leave behind them. And to repeat an earlier statement, these gains are the result not only of geniuses but of a real number of work-a-day ingenious people.
Julian Simon, Ultimate Resource 2, 380 & 385)