For something that’s supposed to be a natural process, breastfeeding can be surprisingly complicated — and not only for new mothers literally strugglingwith the process. Breastfeeding debates can leave families feeling embattledfrom both sides, but controversy over who should breastfeed and for how longand where shows no signs of letting up. For example, in July, news broke that the United States had fought a seemingly uncontroversial resolution in support of breastfeeding at the World Health Assembly earlier this spring.

But, though such controversies can seem like a distinctly modern problem, breastfeeding has long been fraught. When historian Jacqueline H. Wolf began researching the history of breastfeeding, the questions she found American women facing a century ago weren’t so different from those faced today: who gets to do it and how, and what everyone else thinks about that.

With World Breastfeeding Week starting Wednesday, Wolf — who is a professor of the history of medicine at Ohio University and the author of Don’t Kill Your Baby: Public Health and the Decline of Breastfeeding in the 19th and 20thCenturies and, recently, Cesarean Section: An American History of Risk, Technology, and Consequence — spoke to TIME about the historical “baggage” that makes breastfeeding such a controversial topic.

How did you come to research the history of breastfeeding?

I was a graduate student when I was pregnant. I was going to be an environmental historian, but I was sitting in my study beginning that dissertation and lying at my feet was a copy of The Womanly Art of Breastfeeding, and I thought to myself, ‘Breastfeeding! Now that’s a topic historians haven’t looked at!’

Was there anything you found in your initial research that really surprised you?

My central research question was at what point and why did American women begin to bottle feed as opposed to breastfeed. I assumed I’d be writing a dissertation about probably the post-World War II era. I kept going back and back in time trying to find when the change happened, and it turned out it was the late 19th century, so I ended up writing a completely different dissertation — and eventually book — than I had anticipated.

Was there ever a period when breastfeeding was not complicated? I was thinking there must have been one, but then on the other hand you have something like the idea of a wet nurse going way back.

Wet nursing actually was a visible occupation until the 1920s in the United States. We know that from wanted ads in newspapers and from doctors’ papers. Hospitals in the U.S. had wings of wet nurses, who were usually impoverished desperate women. It was not a pleasant occupation. Wet nurses were usually single women who’d been abandoned by their families or the father of their children, and you could see their desperation — mainly because if they went to work for a private family, that private family would almost never allow them to bring [their own] baby with them, so the baby had to be relegated to a foundling home. Really, what it meant was that a wealthy baby lived and a poor baby died. That was the history of wet nursing in the U.S.

Did this make it seem like breastfeeding was something that only poor women did?

It was never that cut-and-dried. There’s evidence of wealthy women who were just heartbroken that for whatever reason they weren’t able to breastfeed. And there’s other evidence of women who were just as happy to hand over their children to a wet nurse. There’s no one answer. Yes, there’s evidence in some ways that it was class-based, especially as time went on, but on the other hand up, until the last 120 years in the United States, if you didn’t supply your baby with your own milk, the chances of the baby dying were very, very great.

When does formula enter the picture?

Interestingly enough, the word formula stems from the 1890s and it literally was taken from mathematical formulas — physicians were absolutely desperate to find a way to save babies’ lives. They thought that they could “humanize” cow’s milk if they could make it mimic the substances they could recognize, like the percentage of fat, the percentage of protein, the percentage of milk sugar. But they also wanted to gear the substance to specific babies, so they had very elaborate theories.

When does formula start being produced by businesses rather than individual doctors and chemists?

It was the Civil War that [widely] introduced canned milk, because that was given to the troops, and it was around that time in the 1860s that a lot of proprietary infant food companies first made an appearance as well. They didn’t tout themselves as being superior in any way to mother’s milk, quite the contrary; they would compare themselves to another infant food. It was around that time Nestlé’s food came on the market, and they touted themselves as being powdered and so not requiring any mixing with cow’s milk, which could be spoiled in urban areas because there were no dairy farms nearby. Cow’s milk at the time was a scandal, which is why infant feeding could be so deadly.

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In many medical fields related to women’s health, there’s a moment where it switches from being something that laywomen and midwives worried about to something that doctors worry about. Is that what happens to breastfeeding?

This goes back to how I ended up looking at the 1880s and the 1890s as a turning point. The U.S. was rapidly urbanizing and industrializing, and that changed everything for American culture. People were starting to work in factories and they had to pay more attention to time. We see the introduction in infant-care manuals of very detailed feeding schedules. The theory was that adults were having a hard time with scheduling, but if you can adapt a baby to scheduling, they wouldn’t have that tough time.

The reason that’s really interesting is that anyone who knows anything about breastfeeding works knows that the more a baby sucks, that’s what stimulates milk production. If you put a baby on a strict schedule, mothers’ milk supplies go down. So you see mothers beginning to complain that they didn’t have enough milk and it was then that the medicalization began, because doctors became involved in what seemed to be a very serious problem of lactation failure. No one connected it to the change in culture and the change in infant feeding habits. The doctors came up with all these theories. One of them was that [lactation] was simply a disappearing function. There was a large group of doctors who feared that when girls were in school during the time they were going through puberty, their reproductive systems were competing with their brains for energy, and their brains were winning — the over-education of girls. The medical community was really worried that they had to come up with a solution for infant health, because they feared that this inability to lactate was going to become a permanent problem.

That’s interesting to think about in terms of what happens in the 20th century as women enter the workforce in greater numbers and need to be on a schedule that’s not a baby’s. How does the history of breastfeeding intersect with the larger history of women’s place in society?

It’s a big reason why any discussion of infant feeding creates so much emotion and controversy. Women who are mothers, that tends to be a big part of their identity. We want to perform well. We want to do the best for our children. It feels very threatening to be criticized. I should say that infant feeding absolutely is a woman’s choice and there are all kinds of reasons why women choose to feed their babies however they decide to feed their babies. But you can’t talk about breastfeeding in the United States without pointing out that every other wealthy country has found a way to accommodate breastfeeding mothers, and usually in the form of lengthy paid maternity leave. It’s very hard for American women to breastfeed, even according to our own medical guidelines, because the social supports are not in place.

So would it be fair to say that the history and the social structure can’t really be separated from those individual choices?

Health choices are rarely truly voluntary, and certainly breastfeeding is a great example of how we may think we’re making a voluntary choice but there’s so much baggage behind it.

When does pumping become a thing?

If you look at the Sears catalog from the 1890s you’ll find breast pumps, but they were for a different purpose. If a baby were born prematurely in that era, often they’d be born too weak to suck. So breast pumps were so they could pump the milk and feed the baby with a spoon or a cup. Pumping didn’t become a major practice until really relatively recently.

The women most likely to breastfeed are privileged women, women who are wealthier, who are college educated, who might have their own offices at work where they can close the door and have some privacy to pump. Pumping has become so common now because so many women work — but it’s become a phenomenon of women who are privileged enough to be able to take time off in the middle of the day.

Where do you think the history is leading us next?

The effect of infant feeding habits on public health was very stark more than a century ago. You didn’t breastfeed a baby, the chances were enormous that the baby was not going to survive infancy. Today, still, the ramifications for public health have been profound. The structure of human milk is largely unexplored territory and scientists are just beginning to look at this truly living substance. It has effects not only on the neonatal gut and immune system but on lifelong health — the list is very long and we’re just beginning to understand the mechanism of action. It’s really important that we be able to have a sane discussion not just about the public health ramifications of not supporting women who want to breastfeed, and that [in doing so] we also look at the formula companies. They have real clout.

I am not anti-formula. Thank goodness formula is safe now, whereas it wasn’t 120 years ago. Thank goodness if families and children and mothers need formula, we have it there. It should be there in case of emergencies, and thank goodness it is.