Throughout the ages, rich or sick women turned their babies over to already nursing mothers, called wet nurses, to feed them through early childhood.
Early in the century, scientists began analyzing the content of human milk, Naylor said. They took "evaporated milk, added sugar, fiddled around with some vitamins," in an attempt to re-create human milk.
Researchers suspected the early formulas had vitamin deficiencies, but at least the babies who were fed that formula survived and grew, Naylor said.
Later when men went to fight in World War II and women went to work outside the house, formula came into use, "in large, large numbers that hadn't been done before," Naylor said.
"People didn't recognize that other losses went along [with the switch to formula]," she said. As one or two generations stopped nursing, the norm became to bottle-feed. And a body of knowledge once passed from grandmother to mother to daughter began disappearing.
By 1971, lactation hit a low point, with only 24.7% of new mothers initially breast-feeding in the hospital, according to La Leche League.
"Many people feel the rate of breast-feeding was lower," said Mary Lofton, spokeswoman for La Leche. The surveys counted even women who nursed once a day in the hospital and didn't continue at home.
By 1982, lactation hit its high point, with 61.9% of mothers nursing in the hospital. In 1995, the latest figures, 59.7% of women initially nursed their babies, with only 23.3% nursing past six months.
The recent AAP policy statement received much criticism for burdening women with keeping up lactation for a year. Said one working mother of twins: "It's all the Super Mom thing. Now let's go to work, and if you get a minute from your desk, let's go to the lactation station."
Lofton finds such criticism ironic.
More working mothers continue to nurse than do stay-at-home moms.
"It is the employed mother who is leading the pack," she said. Lactating mothers tend to be higher income, older and better educated than women who don't. Seventy percent of mothers 35 and older initiate nursing in the hospital compared with 52.6% of mothers 20 to 24.
Lofton said a less obvious, though powerful, reason women choose to use formula is because new motherhood is so overwhelming, nursing is often confused with being forever bound to the baby.
"Going from being somebody's daughter to somebody's mother is a chasm of unbelievable length," Lofton said.
One mother came to a La Leche meeting wanting to continue to nurse her newborn but convinced that it was tiring her out, Lofton said. She stopped nursing but came back to Lofton later, saying, "You know, I weaned, but the baby didn't go away."
Along with the enormous changes in a mother's life, she often has to deal with what Lofton calls a "chorus of voices, husband, mother-in-law, even the man down the street, saying, 'Are you still nursing?' "
And, because the breast is so sexualized in Western culture, the subject of breast-feeding is loaded with confusion.
Both the AAP and La Leche have been criticized for promoting breast-feeding. But Lofton and others say it's a medical recommendation and not a value judgment.
"Parents have the right to hear the data. They can make their own choice. Fear of instilling guilt is a poor reason for not giving a mother information," Lofton said.
For Kiran Saluja of Women, Infants and Children (WIC) and the Breastfeeding Task Force of Greater Los Angeles, the issue is one of public health. "This is easier than bottle-feeding, it is way more healthy and the long-term effects are still coming out."
WIC has often been blamed for encouraging formula-feeding among lower-income women. Saluja admits that at one time, that was true, but there was purpose behind the practice.
"In the '60s, anemia was a huge problem" in low-income communities, Saluja said. Because more than three-quarters of those babies were bottle-fed and often drinking cow's milk by 6 months, infant anemia was endemic. WIC workers went out to the public armed with iron-fortified formula to bolster babies' nutrition, she said.
For the last several years, however, WIC has also heavily promoted lactation. The U.S. Department of Agriculture began funding the new effort in 1989.
"The largest increase in breast-feeding has been among low-income women and among women of color," Saluja said.
Saluja says she is passionate about the subject because, 15 years ago she was misled into formula-feeding her daughter. After the birth, Saluja suffered from what is aptly called "rusty pipe syndrome"--a little blood was coming out with her milk. She didn't realize the blood would stop, and her doctors and nurses encouraged her to formula-feed instead. She has since nursed her two younger daughters.
"It's something that's always moved me. If that could happen to me, I was thwarted in what I wanted to. This is so unfair," Saluja said.
To Saluja, this country has such a "bottle-feeding" culture that "even women who want to do it get daunted at so many steps."