The number of children a woman in America has in her lifetime declined during the past two centuries, and it's not just because of the birth control pill.
Historians are closing in on the socio-economic and cultural factors in family downsizing, a trend also found in most of Western Europe.
"There are two reasons fertility rates can decline," said J. David Hacker, a SUNY Binghamton historian. "One explanation is that marriage declines. Not as many women get married, and if they do marry, they do so at a later age, so that there is less time to have children. The second explanation is that people consciously try to limit having children, which was revolutionary in the 19th century."
According to most census estimates, an American woman had on average seven to eight children in 1800. By 1900 the number dropped to about 3.5. That has fallen to slightly more than two today. Birth rates fell first in New England, and then among pioneers as they headed west. Internationally, France led the way to smaller families.
Reconstructing the intricacies of census data has been difficult for dates prior to 1933, when the National Birth Registration system was put into place. With grant money from the National Institute of Child Health and Human Development, Hacker is taking a closer look at long-term census trends thanks to a new database developed by the Minnesota Population Center.
Modern economics have made smaller families a good investment, historians and economists agree.
Before the 1800s, children were educated at home or in church. Children became more expensive to care for and less helpful around the house once public schooling became available. At the same time, women were freed up from all-day children-rearing, allowing mothers to enter the paid labor force.
However, money isn't the only incentive for smaller families, experts say.
"We know for sure that you don't have to reach a high level of per capita income for fertility to decline, but we don't know exactly what sets it off," said historian George Atler at Indiana University. "Whether it's general change or attitudes about birth control is still a question debated among demographers today."
The dogma of most major Christian religions during the 1800s forbade abortion and divorce in the United States. And in 1873 the Comstock Act made it illegal to send any so-called obscene materials in the mail, including information about contraception.
Ironically, Hackler said, record sales of two family planning books published in the 1830s suggest that the public was eager to keep families small, regardless of religious or political pressure.
"There's a flurry of publications in the mid-19th century giving readers advice on how to control family size," Hacker told LiveScience.
"Moral Physiology" by Robert Dale Owen and Charles Knowlton's "The Fruits of Philosophy" became popular for advocating contraception methods. Owen described coitus interruptus, where a man ejaculates outside of the woman's body. Knowlton's book included instructions for women on how to wash with a spermicidal solution.
Hacker's research may better inform economists and policy makers about current worldwide trends toward smaller families.
"All nations are experiencing fertility declines," said Hacker. "It's becoming a social policy issue as countries face prospects of caring for an aging population."