In a photo posted on Facebook, 26-year-old Jessica Anne Colletti is smiling. She's breast feeding two babies at the same time and cheerfully writes: "My son on the right is 16 months and my friend's son is 18 months. I watch her son while she works and have been feeding them both for a year! So much love between these milk siblings, it's a special bond between us all."

The intimate picture, shared on the Facebook page for Mama Bean, a blog that focuses on attachment parenting and breastfeeding, brought strong reaction from both sides. "Gross!" is how a number of commentators described it. Others rallied behind Colletti, praising her for helping her friend and saying they would do the same if asked. "I think its beautiful and society sadly, has lost its 'it takes a village' approach," one person commented.

In a longer explanation since the controversy broke, Colletti wrote that "breastfeeding my friend's son came naturally to me." She said she started babysitting the child when he was five months old. Since she was already breastfeeding her own son, who was three months old at the time, she began to nurse the other child, too, as he was having issues with the formula he had been given.

"My friend struggled with breastfeeding in the beginning and succeeded for 9 months. She was always very happy that her son had the nutrition and comfort he needed while she was working. Being able to breastfeed her little boy has created a special bond between us all, a bond I will always cherish," she said.

Colletti is hardly the first to cause a stir for breastfeeding someone else's baby.

In 2008, actress Salma Hayek made headlines when she was filmed on a UNICEF goodwill trip to Sierra Leone breastfeeding a local infant who happened to be hungry. When later asked by "Nightline" what she thought her daughter would think, Hayek replied, "I actually think my baby would be very proud to share her milk. And when she grows up I'm going to make sure she continues to be a generous, caring person."

While the practice may make some people in the United States squeamish today, it has been common from the time of ancient Romans -- when upperclass women would employ others to breastfeed their infants -- until the 20th century -- when baby formula was invented. An article last year in the New Republic noted that wet nurses "have fed some of the most famous babies in fiction and myth — from Rebecca, the Biblical wife of Isaac, to Muhammad to Shakespeare’s Juliet. Louis XIV was painted suckling at the breast of a woman who was not his mother."

The World Health Organisation explicitly endorses the practice. In its "Global strategy on infant and young child feeding," the WHO lists breast milk from "a healthy wet-nurse" as one of the best alternatives to breastfeeding your own child.

In recent years, feminists around the world have extolled the virtues of informal communities of women breastfeeding each other's children, with some arguing that this could relieve the burden on modern-day working moms.

Gabrielle Palmer, a British breastfeeding advocate, has called the practice a "unique opportunity for solidarity and friendship among women."

Rhonda Shaw, a senior lecturer in social and cultural studies at the University of Wellington in New Zealand, has written about the "yuk factor" of "cross-nursing," which she describes as an informal arrangement distinct from from wet nursing, which is more contractually based.

Shaw has said that this practice disrupts the "Western ideal of the individualist or exclusive model of maternity that places the entire burden of a child's care on the backs -- or breasts -- of its biological model."

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