Here in northern India, Austin and I met a mother, Maher Bano, whose daughter had been born at home just hours earlier. The baby was underweight and in danger of dying. The best medicine in this context is breast milk: Studies from India, Nepal and Ghana show that prompt breast-feeding reduces neonatal mortality by 44 percent.

But Maher Bano said that for the first 24 hours, the baby would be given only tea with honey.

“I’ll breast-feed the baby tomorrow, or the next day,” she said, explaining that she was following the guidance of the traditional birth attendant who had helped her deliver the baby and cut the cord. This is common: Worldwide, only 43 percent of babies are put to the breast within an hour of birth, as recommended by the World Health Organization.

One reason for delays is suspicion of colostrum, the first, yellowish milk, which doesn’t look quite like milk but is packed with nutrients and antibodies; it’s sometimes called the “first immunization.”

Another big challenge: In hot countries, villagers also often give infants water on hot days, or start them on food before six months. Water both displaces milk and also is often contaminated. (Breast milk, in contrast, is safe even when the mom drinks contaminated water.)

Western companies are also to blame. Manufacturers of infant formula face stagnant growth in Western countries, so they aggressively pursue poorer countries. Researchers found that 85 percent of recently discharged mothers in Phnom Penh, Cambodia, had seen advertising for formula.

Some also believe that Western entertainment has sexualized the breast in ways that reduce breast-feeding.

While the clearest benefits of breast-feeding have to do with saving lives, there is also some evidence of other health and cognitive gains. In Belarus, children of women randomly assigned to exclusive breast-feeding promotion scored six points higher on I.Q. tests than controls.