That is the prediction of anthropologist Virginia Abernethy, professor emerita of psychiatry at Vanderbilt University, speaking on Feb. 13 in the symposium "From the Ground Up: The Importance of Soil in Sustaining Civilization" at the annual meeting of the American Association for the Advancement of Science held in Seattle.
"The availability of energy has been a major factor in population growth," said Abernethy. "In the modern context, energy use per capita affects economic activity. So a prolonged decline in energy use per capita will tend to depress the economy which, in turn, will cause a decline in the fertility rate."
Abernethy's argument has two parts: the link between the availability of petroleum and the economy, and the link between changes in economic conditions and fertility rates.
Regarding the first link, she points out that oil and gas are "unparalleled" sources of energy. Not only does petroleum provide the fuel that powers modern vehicles and the natural gas that people use for home heating and cooking, but petroleum products are the source for hundreds of industrial and agricultural products, including fertilizer, pesticides and plastics. This means that petroleum cannot be easily replaced by other fuels and feed stocks.
Despite the fact that continuing low prices are encouraging Americans and the inhabitants of other industrialized countries to consume oil and gas at profligate rates, "numerous geologists, physicists and computer scientists have calculated that petroleum and liquid natural gas production will begin to plateau and then decline within five to 10 years," she said.
Such a downturn will have major economic effects, Abernethy expects. In the United States since World War II, rising oil prices have preceded most U.S. recessions and unemployment rates have risen following significant increases in the real price of oil.
"Higher priced energy may force policy-makers to think of economic recession or slow growth as the usual state, and force farmers to rethink agricultural inputs. The shift away from high inputs to soil-conserving technology is theoretically ideal from the perspective of moving to a sustainable agricultural system. The downside, however, is that crops will be smaller and food costs higher – probably much higher – than with industrial agriculture," she said.
The second link, from economic change to the fertility rate, is based on a theory called the "economic opportunity hypothesis" that Abernethy first proposed more than 30 years ago. According to her hypothesis, people increase the size of their families when they are convinced that economic opportunities are expanding and decrease family size objectives when they believe that resources are shrinking and the difficulty of raising children is increasing.
What is important in this regard is not how rich or poor a society is, but the perception its people hold about how things are changing. When the future appears threatening, for example, people tend to exercise reproductive caution and adopt such measures as marrying later and putting more space between births within marriage.
According to Abernethy, this correlation holds true over the entire socioeconomic range and its predictions differ substantially from the conventional view that increasing educational levels in a society by itself can reduce fertility rates.
Abernethy uses recent U.S. history to support her proposed energy-fertility link.
The 15-year burst in fertility rates that followed World War II, known as the "baby boom," was accompanied by the widespread substitution of energy-intensive technology for labor that substantially improved productivity. Higher productivity and labor shortage in an expanding economy produced an increasingly large and affluent middle class that "responded with early marriage and closely spaced births." The baby boom ended within a year following rising energy prices and the 1961 recession.
Fertility rates fell to the lowest level ever recorded in the United States following the oil-induced recession of 1980-81. Both white and black fertility rates plunged below replacement level.
In the late 1980s, lower oil prices and other factors encouraged rapid job growth. Nevertheless, the bottom half of wage-earners enjoyed little increase in real income. So fertility rates rose only slightly and the recession at the beginning of 1990 reversed the modest upward trend.
"The improving standard of living to which many societies have become accustomed will be difficult to maintain in the face of rapidly rising prices for energy. In these circumstances, fertility rates are unlikely to rise. Indeed, a future marked by declining energy use per capita may be the ultimate driver of worldwide declines in fertility," she wrote.