Biological determinism: The “natural” range of weaning

I’m not quite ready to let go of Kathy Dettwyler quite yet. Dettwyler is the author of a scholarly paper which I’ve read but cannot find, unfortunately, but a layperson’s version can be found at her site, which claims that the natural range of weaning for humans is 2.5-7 years.That is, supposedly all human children would cease nursing between those ages if our (stupid and unnatural, it’s implied) cultural biases weren’t involved. She bases this upon various extrapolations made from the animal, and particularly the primate, world – animals wean when they reach a certain weight, or grow certain teeth, and what not.

I’m sure Dettwyler is correct in the particulars of her descriptions of the animal kingdom (though I’m hard pressed to know which “pediatricians” she claims to have culled this knowledge from. I know precious few pediatricians who are also comparative zoologists), but it’s all really beside the point: the way the information was gathered about the animal kingdom was by observation, not by extrapolation. We should be applying the same standard when studying humans. And as Dettwyler herself says (and I have no reason to disbelieve her):

In societies where children are allowed to nurse “as long as they want” they usually self-wean, with no arguments or emotional trauma, between 3 and 4 years of age.

This, therefore, is what we’d expect to be the “natural” (i.e, rules-less) age of weaning. What’s more, this actually corresponds to what pre-industrial societies do: in a large study about infant feeding patterns, spanning nearly a century of anthropological research about 133 different nonindustrialized societies, the average age of weaning was 29 months, with a range of 12-66 months (1-5.5 years). The authors noted (emphasis mine):

Classical evolutionary biological approaches have focused on the adaptive aspects of weaning in relation to life history and aimed to infer a human pattern from analysis of nonhuman primate data. Cross-species comparisons have generated several models to predict ages at which primates are adapted to terminate lactation, which include: 1.5 times the length of gestation , eruption of first molar teeth, tripling or quadrupling of birth weight and attainment of one-third adult weight. Unfortunately, the range of variation in weaning patterns within and between species of nonhuman primates has yet to be fully described and explained, and no model reliably predicts age at weaning for all primate species. When applied to humans, each model yields a wide range of predicted values due to variation in birth and body weights across populations, most likely because they do not incorporate the modifying effects of diet, work activities, culture, social organization and technology. Independent characterization of species-typical values for human weaning parameters will facilitate evolutionary analyses of human life history traits.

See, what Dettwyler’s overlooking is that it’s an inseparable part of human nature to create cultural rules – about weaning and everything else. Therefore, trying to extrapolate what humans would do if they were driven solely by biological forces is about as useful as speculating what humans would breathe if they had gills.

One of Dettwyler’s assumptions especially rankles in that regard: she claims that since the human immunological system isn’t fully developed until age 6 (true to an extent), some humans breastfeed until that age and beyond. However, if breastmilk were necessary to boost children’s immune system until it became fully functional, we’d expect all human societies – especially primitive ones with no access to antibiotics or modern hygienic practices – to nurse that long. The fact that the overwhelming majority of the world’s children don’t should be evidence enough that this assertion is bogus.

I would also submit that just because certain things may be “biologically correct”, doesn’t mean they’re actually the correct thing to do. For example, most girls in the western world develop reproductive ability between the ages of 8-16 years. Would any anthropologist be so bold as to suggest that girls as young as 8 should be reproducing, just because they can? It’s also biologically correct to walk around naked – after all, nobody is born clothed – but except for a handful of nudists, nobody actually walks around without clothing. Especially not outside, in mid-January!

I’m sure Dettwyler would absolutely love this family (short video). But Is this type of absolute worship at the Shrine of the Breast really natural to humans? I really hope not.

Unlike that woman in the video, Dettwyler acknowledges that the importance of breastfeeding diminishes as the infant grows into a child. She makes an amusing analogy about how even small amounts of breastmilk matter:

“Clearly the phenomenon of diminshing returns is at work here — the first six months of breastfeeding are clearly much more important in terms of the baby’s nutrition and immunological development than the six months from 3.5 to 4.0 years. That doesn’t mean that you shouldn’t continue to provide breast milk if your baby wants and you don’t mind. It would be like saying, “Well Mabel, we don’t get very much income from that oil well anymore. Used to get $56 a month in royalties, now we’re lucky if we get $25 a year. Guess we should tell that oil company just to keep their durn money.” And Mabel says, in return “Good grief, Clyde, don’t be ridiculous. That check still buys $25 worth of food. Where has your mind gone to now?””

I don’t know about Clyde, but if I all I were getting was a measly $25 in royalties from my proverbial oil well, I’d sell the land it stands on to the highest bidder and put the money in a high-yield CD. Or in real-life terms, I’d take the body attached to those lactating breasts and go do something else with it. Because, contrary to what Dettwyler asserts, breastfed children of that age (2 and beyond) have not been proven to be significantly “healthier, smarter or happier” (where on Earth does she get that last one?!) than other children.

UPDATE Jan 27th – a bit more on the subject here.

UPDATE #2 May 1st – and yet more.

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10 Responses

  1. Excellent analysis. I am always annoyed at cross-species comparisons that pretend cultural invention isn’t an inherent part of our culture.

  2. one question, do you breastfeed?

  3. Dayna,

    I’ve blogged about my breastfeeding experiences here. I don’t necessarily think you need breastfeeding “street cred” for a post like this, though. I imagine I’d write the same thing if I were a man or a childless woman.

  4. That is Veronika in the video… it was part of a documentary which aired on Channel 4 in the UK called ‘Extraordinary Breastfeeding’ in 2006

  5. I know. I wrote a post about her later on, here .

  6. You are clearly not a scientist. You don’t understand my research, and indeed, you admit you haven’t actually read it, even thought it is available online with a basic google scholar search. I have never said that children “should” breastfeed for any length of time. My research addresses what the natural age of weaning would be in modern humans IF we didn’t have cultural beliefs. Of course, we do have cultural beliefs, and I’ve discussed this extensively in my work. Before you go around trashing people who do scientific, peer-reviewed, scholarly research, you might want to make a little bit more effort to actually read it. And if there are parts you don’t understand, I’ll be happy to explain them to you. In the unsourced quote that you provide, the author says my research includes a model of breastfeeding for 1.5 times the length of gestation, but that is incorrect. The correct ratio is 6 times the length of gestation, or 4.5 years.

    • I had read your article but couldn’t find it for the purposes of this blogpost to link to it. Which you’d have known if you’d bothered to read the blogpost with any care. And it seems I understood your article (scholarly and popular) quite well, as you’ve just reiterated what I said about it. The point is that there exists no human society – and probably has never existed, either hunter-gatherer, rural or modern – without cultural beliefs and practices, hence speculating about how long humans might breastfeed under non-existent conditions serves no practical purpose whatsoever and should certainly NOT be used as a guideline to how long humans *should* nurse. Nor should the word “natural” be conflated with “optimal” or “uniformly best”. Nature (or rather evolution) doesn’t do that. And while you may not have claimed this yourself, you can hardly be unaware of the misuse of your “research” precisely to that end.

      Just like when you want to know what is natural for gorillas, you go observe gorilla behavior, the correct way to determine human behavior is to observe human behavior, which is what the study I linked and whence the quote you take issue with came from did, and it came up with a far lower estimate of “natural” breastfeeding duration than yours. Again, reading comprehension is important, Kathy. Even more than bloviating about being a scientist and having peer-reviewed research. You also are clearly no doctor, and shouldn’t be making far-reaching statements about the result of medical research you clearly don’t understand (such as the real magnitude of breastfeeding benefits and their impact on mothering abilities or happiness).

  7. You write: “However, if breastmilk were necessary to boost children’s immune system until it became fully functional, we’d expect all human societies – especially primitive ones with no access to antibiotics or modern hygienic practices – to nurse that long. The fact that the overwhelming majority of the world’s children don’t should be evidence enough that this assertion is bogus.”

    First of all, there are no such things as “primitive” societies. You aren’t better than people, or more advanced, or more intelligent, or more moral, or anything — than people living anywhere in the world.

    In societies where people have no access to antibiotics or modern hygienic practices, they often have access to traditional medicine and traditional hygienic practices, which are often quite effective. If they weren’t, all the kids would die before reaching adulthood.

    In fact, in many rural populations with marginal nutrition and lots of diseases to contend with and no access to antibiotics or immunization, up to 50% of the children did die before the age of 5. Just another example of how parting ways — culturally — with the biological underpinnings of evolved human physiology, can lead to serious consequences.

    We have a number of cultural adaptations that have helped us “get away” with not nursing for 5-6-7 years and still produce enough children that we are rapidly exceeding the carrying capacity of the planet. The earliest such cultural adaptation was the discovery of the making and control of fire, especially for transforming food. The second was the Neolithic Revolution (domestication of plants and animals). Instead of having only a few kids, 6-7-8 years apart and having them all (or almost all) survive to adulthood, humans early on adopted a pattern of earlier weaning so that they could have children closer together, and more of them — up to 10 — across a woman’s reproductive career. Even if 4 or 5 of them died from being weaned too early, they still have more than enough surviving children to replace themselves and grow the human population of the planet.

    This is all a much more complicated, and interesting, issue than you seem to think.

    • I disagree that there are no humans who’d manage to survive without any medical intervention (traditional or otherwise- those pesky cultural interventions again!). The % of surviving children would surely be much lower without any healthcare whatsoever, but I doubt that it would give us infant/child mortality rates of 100%. As it is, even with breastfeeding and without modern medical intervention, infant mortality is rather dismal – I seem to remember seeing figures of 20-40% under-5 mortality for hunter-gather societies, even when infans breastfeed for many years, though I don’t know of ANY human society where all children routinely nurse until age 6. (Oh dear. Did just about every human ever alive “part ways with the biological underpinnings of human society”? Wonder why that is?). Breastfeeding plays an important role in infant survival in those societies for sure, but is hardly a panacea. And evolution’s lack of optimality is well demonstrated here. It’s certainly not the force that explains our current planet-overwhelming reproductive rates.

      Indeed, it’s a very complicated and interesting issue. However, you’re the one with the misconceptions, I think. Our modern society, with its medical interventions (including hygiene, immunizations and infant formula), allow us to “part ways with the biological underpinnings of human society” and get away with it as never before, and with few if any serious consequences. We’ve come to expect infant survival rates of close to 100%. The beneficial effect of breastmilk, in the big picture, is kind of small these days (if it exists at all). Even with the other non-survival related benefits (which can’t always be differentiated from confounding variables and are often much smaller in magnitude than advertised), there’s no denying that many children not only survive, but thrive, on formula, and that you really can’t tell how a child was fed just by looking at them or at any other health measure.

      You might want to remember that next time you’re thinking of bullying some mother on Facebook because she had the temerity to have a child and not breastfeed it. Eh, Kathy?

  8. Oh, and Kathy, in case you’re not just hit-and-run posting, maybe you’ll share the scientific rationale behind the following screed you posted on Facebook some months ago on a fellow breastfeeding bully’s page:

    “Reasonable people understand that “in nature,” without intervention, sometimes mothers and babies die, who could have been saved if they’d had access to modern medical care. They also understand that Western medicine has gone way beyond “medically necessary” interventions to the point that modern ob/gyn/labor&delivery care
    now causes as much – if not more — damage than it does good. One of
    the problems with a rational evaluation of the topic is that it’s easy
    to say “A child’s life was saved by intervention” and place some sort of
    value on that. It’s not so easy to place a value on the hundreds of
    thousands [millions?] of children whose lives were permanently harmed by unnecessary c-sections, unnecessary separation from mother, unnecessary interventions such as routine fetal heart monitoring, epidurals, early cord cutting, suctioning, hatting, swaddling, vigorous scrubbing baths, immediate eye drops, immediate circumcision, formula supplementation, etc. etc. etc. How does one begin to do the math? If we harm 10,000 children to various degrees, is that worth it to save the life of one child? What if we harm 100,000 children through our interventions, but save the life of one child? There is no way to compare the outcomes. But there is no shame is asking medical professionals to rethink how they approach childbirth, to dial back the interventions and use them only when medically necessary or when proven to be helpful, rather than harmful. “Evidence-based medicine” that relies on current research tells us that all of the interventions mentioned above (routine fetal heart monitoring, epidurals, early cord cutting, etc.) do NOT lead to improved outcomes in terms of maternal-child health. On the contrary, they are harmful. Yet they too often remain part of “traditional Western childbirth practice” – even against the mother’s wishes.”

    Of course, if you knew anything about evidence-based medicine, had ever even read and understood a medical article, you’d know that such risk/benefit assessments are made constantly, that many “unnecessary” procedures ca only be determined to be so in retrospect, and that “harm” is not defined by most people as losing their bragging rights about their birth at the local LLL meeting. Most of us sane mothers define harm as those dead and injured babies you seem to treat so cavalierly.

    And speaking of harm, I’m sure you’ll be happy to expound to my readership about the immense harm to the babies from the evil practice of hatting you mentioned. Using scientific, peer-reviewed articles from respectable journals mind. I’ll wait. 🙂

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