It raises the question not just about twins but also about wet nurses. I mean its a pretty normal tradition for mothers to 'outsource' their breast feeding to other mothers, especially if they're tired or sick.
What about formula milk? The long term benefits of breast feeding are so tenuous that I can't imagine there's a practical significance to the difference between breast milk produced for girls versus boys in human babies: http://www.skepticalob.com/2013/05/world-health-organization....
Studies like these are valuable, but it's tempting to jump from interesting observation to policy recommendation without keeping in perspective (or even bothering to quantify) the magnitude of the impact.
The long-term benefits may be tenuous or as-yet undetermined, but the short-term benefits are so overwhelming that the WHO paper to which you link states quite clearly, citing the WHO Global strategy for infant and young child feeding:
Given such evidence, it has been recommended that in the first six months of life, every child should be exclusively breastfed, with partial breastfeeding continued until two years of age.
That's WHO guidance. They don't broker much consideration for formula milk in that statement.
The WHO isn't just giving advice to mothers in America, they're giving advice to mothers in Bangladesh and other developing countries. Indeed, that's their primary audience. The short-term advantages of breastfeeding are extremely relevant to mothers in countries where the water may not be clean and where babies are constantly exposed to high levels of pathogens. Those considerations are far less relevant to babies born in the first world.
It's stupid to take WHO recommendations, or medical recommendations generally, at face value, because they generally are devoid of any cost-benefit analysis. Take this study of short-term benefits done in the U.K. http://pediatrics.aappublications.org/content/119/4/e837.ful.... It found a 53% reduction in diarrhea hospitalizations from exclusive breastfeeding, and a 27% reduction in lower respiratory tract infections. This is a very strong result and justifies the "breast is best" recommendation. Yet, when subjected to cost-benefit analysis, the result isn't so clear. The incidence of these conditions in the sample of infants was only 1-3% to begin with. In other words, exclusive breastfeeding reduces the chance of a diarrhea hospitalization from 1.1% to 0.5%, and for a lower respiratory tract infection from 3.2% to 2.3%. And remember, both conditions are easily treatable.
On the other side of the scale, exclusive breastfeeding guarantees that the mother will be saddled with the primary role of feeding the infant for six months to a year and cannot easily delegate the task to the father (even with pumping, the father remains wholly dependent on the mother). Does a statistically significant, but small, reduction in an unlikely outcomes really justify blanket recommendations to exclusively breastfeed? Do you apply that same sort of extreme caution to every parenting choice? Given that motor vehicle crashes are the leading cause of death in children at every age from 2-14, shouldn't the WHO recommend that everyone move out of the suburbs into cities where they don't have to drive?
> The long term benefits of breast feeding are so tenuous
This is a joke, right?
Simple reasoning and deduction will lead you to the right answer. We evolved to drink the milk of our mothers, not a chemical concoction derived from the milk of cows fed by corn.
Actual data are more valuable than "simple reasoning and deduction" when matters of the physical universe--of which the biology of breastmilk and its benefits are a subset--are concerned.
I can easily see the possibility that long term benefits are masked or "washed out" by other factors. Short term benefits, on the other hand, are unequivocally and easily empirically established. The fact that immune systems and richer nutrients are passed through breastmilk undeniably give breastfed babies an advantage over formula-only babies.
We also evolved with immune systems. This does not mean that supplementary tools such as antibiotics and vaccines are not useful.
I believe rayiner's point is that infants can thrive on formula milk as well as breast milk. Please don't mock parents who choose to formula feed; there are many cases where it is preferable and/or necessary, just as there are cases where it is necessary to use antibiotics to supplement the body's immune system.
No, my contention is more pointed: the theoretical short-term advantages of breastfeeding are largely irrelevant in the developed world where babies aren't susceptible to infection anyway, and, when considered rationally in the general case, the inconvenience of breastfeeding outweighs any advantages of formula feeding.
Remember, the couple of generations of Americans grew up on formula feeding. Breastfeeding rates were down to the 20% range in the 1970's. Yet, there is very little evidence showing any long-term negative impact in those generations.
> Please don't mock parents who choose to formula feed; there are many cases where it is preferable and/or necessary
And where have I done that? Formula is a fantastic invention that can specifically assist in very difficult situations.
But just as it is clearly inferior to take antibiotics daily because it is too inconvenient to wash one's hands ... so to is it clearly inferior to use formula when the mother is capable of breastfeeding, but can't be bothered.
The real question is whether formula is inferior in any way that matters in the developed world. My contention is that it's not, and in the general case, the inconvenience of breastfeeding greatly outweighs any theoretical advantage from breastfeeding in first world babies.
Babies in the first world are: 1) not exposed to that many dangerous pathogens to begin with; and 2) in the rare cases they do become infected, are easily treated with antibiotics, etc. Sure, breast milk has live immune cells, etc, but does that matter in any practical way?
While I can certainly see the downsides of abusing antibiotics, I don't "clearly" see comparable downsides, in likelihood or magnitude, to using formula.
Formula lacks the live immune system cells the mother passes to the baby. Maybe someday we will develop nanobots to substitute for that. Till then, that's a clear downside.
That was not the question, and even people who accept that should understand that breast milk is not always an option, for instance for the father I know whose wife died shortly after they had a child.
I have nothing constructive to say about the article, but for the record: gender is chosen, sex is not. I wish the world would get this right, especially Scientific American, which got it wrong in the second sentence.
The world doesn't seem to agree with you. Straight from Wikipedia [1]:
Gender is the range of physical, biological, mental and behavioral characteristics pertaining to, and differentiating between, masculinity and femininity. Depending on the context, the term may refer to biological sex (i.e. the state of being male, female or intersex), sex-based social structures (including gender roles and other social roles), or gender identity. ... the meaning of gender has undergone a usage shift to include sex or even to replace the latter word. .... Gender is now commonly used even to refer to the physiology of non-human animals, without any implication of social gender roles.
>The modern academic sense of the word, in the context of social roles of men and women, dates from the work of John Money (1955), and was popularized and developed by the feminist movement from the 1970s onwards (see Feminism theory and gender studies below). The theory was that human nature is essentially epicene and social distinctions based on sex are arbitrarily constructed. Matters pertaining to this theoretical process of social construction were labelled matters of gender.
I think most places people hear it is that gender is the male/female/other self-description, and sex is the physiological state.
Most transgender social justice warriors or gender studies majors maybe. Not most people in general.
The vast majority of the people out there don't distinguish between gender and sex. Especially since only about 0.5% of the population identifies as a gender other than their physical sex.
There's a lot of terminology that the vast majority of people understand poorly. By itself, that hardly seems a good reason for a (supposedly) scientific magazine, particularly when using 'sex' exclusively would understood by everyone.
It probably comes down to the fact that the people practicing physical "hard" sciences do not particularly care about or trust the conclusions drawn by the "softer" sciences (sociology, gender studies, psychology)
I think you're confusing the sociological/social justice definition of gender with the literal one. In the case of the latter, sex and gender are synonymous.
I could imagine some sort of organ senses - child has certain hormones (eg testosterone) in salive, and certain receptors on the nipple pick up on these hormones and then tailor the milk.
Note that I have no basis for this claim, but one of the many ways the body communicates is through hormones, so it certainly wouldn't be outside the realms of possibility...
I don't think the mechanism is a direct biological signaling of the baby's sex to tell the woman to produce fattier milk. It seems more plausible to me that wealthier families value boys a lot more - you see this tendency everywhere. This causes mothers to value their male children disproportionately, and the social feedback she gets probably affects her hormones as well, which would cause the milk to vary. So you see the large difference in wealthier women's milk for boys and girls, whereas the difference in poorer women's milk may not even be statistically significant.
I think if you repeat this test on different circumstances where the child is valued or not, whether boy or girl, you will find similar results that remove the sex factor.
Surely the cultural explanation doesn't extend to similar behavior found in grey seals, red deer, and rhesus macaques? Convergent evolution is always a possibility but it seems like the likelihood lies with a biological explanation vs a cultural one.
"These findings could have implications for formula, which could be tweaked to optimize development for both boys and girls."
As the father of a little girl, I find this sentence more ominous than was probably intended. The formula aisle is already overly complex with Regular, Iron Enriched, Omega Enriched, Soy, Low-Lactose, and No Lactose, among the many yogurt sounding ones (pre/macro/post/whatever-biotic).
However, I am worried (perhaps due to cynicism) that instead of rationally simplifying this system, it might be dumbed down to Boy and Girl formula. Though I guess there may be benefits as well. sigh - glad I'll probably be done having kids by then :D
If this result is valid, it's probably also true for other mammals that bear young one at a time. If so, it's proabably a lot easier to verify in cows than humans. Less paperwork required for experiments, for one thing.
From the article: "These findings, published in the American Journal of Physical Anthropology in September, echo previous work that showed milk composition varying with infant gender in gray seals and red deer and with infant gender and the mother's condition in rhesus macaques."
