These two loops essentially dominate the story of human history since the beginning of the agricultural age some 10,000 years ago. Rising living standards lead to higher population levels lead to higher levels of economic production lead to higher living standards and so on (Loop R1). Compounding the growth rate of R1 is that rising living standards have also led to more economic production on a per capita basis (Loop R2). These are referred to as reinforcing loops because a rise in one variable leads to a rise in the other, which in turn leads to a further rise in the first. The behaviour over time of such a loop is either exponential growth or exponential decline. Exponential growth is reflected in the data from the modern era.