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.
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.
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."
[+] [-] gmuslera|12 years ago|reply
[+] [-] brosco45|12 years ago|reply
[+] [-] cup|12 years ago|reply
Also what about formula milk?
[+] [-] rayiner|12 years ago|reply
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.
An excellent blog post on the state of research into breast feeding: http://www.skepticalob.com/2013/06/two-crappy-new-breastfeed...
[+] [-] brosco45|12 years ago|reply
[+] [-] nappy-doo|12 years ago|reply
Here's an interesting link: https://books.google.com/ngrams/graph?content=gender%2C+sex&...
[+] [-] crazygringo|12 years ago|reply
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.
[1] http://en.wikipedia.org/wiki/Gender
[+] [-] ebfe|12 years ago|reply
[+] [-] TazeTSchnitzel|12 years ago|reply
[+] [-] drpgq|12 years ago|reply
[+] [-] tantalor|12 years ago|reply
http://www.latimes.com/health/boostershots/la-heb-women-brai...
[+] [-] jurjenh|12 years ago|reply
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...
[+] [-] seiji|12 years ago|reply
[+] [-] mooism2|12 years ago|reply
[+] [-] AmVess|12 years ago|reply
[+] [-] nicholas73|12 years ago|reply
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.
[+] [-] wutbrodo|12 years ago|reply
[+] [-] haversine|12 years ago|reply
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
[+] [-] jonah|12 years ago|reply
[+] [-] Nursie|12 years ago|reply
[+] [-] ohwp|12 years ago|reply
[+] [-] TazeTSchnitzel|12 years ago|reply
Sex. Infant's sex. Gender is rarely known at that stage.
[+] [-] unknown|12 years ago|reply
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[+] [-] 1humanwoman|12 years ago|reply
Would love your thoughts!
[+] [-] gweinberg|12 years ago|reply
[+] [-] vwinsyee|12 years ago|reply
[+] [-] grandinj|12 years ago|reply
[+] [-] jacalata|12 years ago|reply
[+] [-] beat|12 years ago|reply
[+] [-] timini|12 years ago|reply
[+] [-] kimonos|12 years ago|reply