"Exclusive breastfeeding is ideal nutrition and sufficient to support optimal growth and development for approximately the first 6 months after birth....It is recommended that breastfeeding continue for at least 12 months, and thereafter for as long as mutually desired."
-- American Academy of Pediatrics Policy Statement on Breastfeeding and the Use of Human Milk
That's a remarkable statement in two ways. First, it's remarkable that any group in a country with arguably the largest penetration of formula feeding in the world, let alone one with a history of financial support from formula companies, would make such a strong statement in favor of breastfeeding. But second, it's remarkable that such a statement should need to be made at all. As mammals, we are defined in part as animals who suckle their young. How can breastfeeding for the human animal be any more controversial than breathing?
The answer, of course, is that humans are shaped by culture as much as by biology. This collection of essays, published in 1995, seeks to pull together a variety of medical, anthropological, sociological and other evidence to examine and understand the practice of breastfeeding. Heavy with citations and serious analysis, the 14 authors here bring to bear a wide variety of viewpoints and help us see the biological roots of this complex phenomenon. Along the way they make an argument, sometimes explicit and sometimes implicit, that the benefits of extended breastfeeding are substantial for both child and mother.
One of the more interesting starting points is the essay by Katherine Dettwyler, "A Time to Wean: The Hominid Blueprint for the Natural Age of Weaning in Modern Human Populations." Dettwyler looks at physiological and biological studies in human and other primate populations that correlate weaning with things such as the eruption of teeth, the percentage of adult body weight obtained, the growth of the infant, or the age of gestation across a variety of primate species. Her conclusion stands in contrast to modern American weaning practice: that the "natural" age of weaning (difficult though that is to define) is somewhere between 2.5 and 7 years of age. (Readers who are not familiar with patterns of parenting may not be aware that there is, in fact, a substantial population of US mothers that nurse their toddlers and believe in "child-led weaning"). That this natural age can be subsumed in the common American practice of weaning by 12 months is testimony to the power of culture in breastfeeding patterns.
Valerie Fildes looks in a different direction in her "The Culture and Biology of Breastfeeding: An Historical Review of Western Europe". While the historical data is fragmentary and sometimes difficult to interpret, it's clear that the rise of substitutes for breastmilk, which became near-universal in some parts of Europe in historical times, had a severe negative impact on childhood mortality. Try to imagine, for example, a society in which 4 out of 10 infants died by the age of 1, as happened in some parts of Germany where artificial foods were widely substituted for breastmilk. Fildes also discusses the practice of wet-nursing as well as the disastrous one of dry-nursing (feeding infants a pap of grain or bread in water): "The usual mortality of dry-nursed infants was put at two-thirds by some contemporary authors, five in six by others, and, in the case of some London parish infants, 90-100%." (Figures for 18th century England).
Other authors explore the politics of lactation (with particular reference to the practices of formula companies in the third world), the artificial conception of breasts as erotic organs rather than functional ones, and the importance of support from family and community on successful breastfeeding. Several authors review the medical evidence: Allan Cunningham catalogs the correlations between bottlefeeding and a long list of infant diseases (diarrhea, respiratory illness, earaches, bacteremia, meningitis..) and looks at the long-term health implications of breastfeeding as well. James McKenna and Nicole Bernshaw speculate on the part that breastfeeding may play, along with infant-parent cosleeping, in the prevention of SIDS. Peter Ellison looks at the natural contraceptive effect of extended breastfeeding, and points out the maternal health consequences of removing this protection in the absence of reliable birth control. And Marc Micozzi reviews a number of studies which, while not conclusive, suggest that breastfeeding helps protect against breast cancer in both mother and infant.
Overall, this is an impressive body of work. The authors, while clearly in favor of breastfeeding, do their best to point out the areas where they're making assumptions or where more research is needed. If you're a prospective parent with a bent for academic literature, I'd consider this book indispensable. Even if you're not a parent, it's worth reading and pondering what it means to be human and how a thick layer of culture builds up atop our basic biology.