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Bananas for Boys. 
23rd-Apr-2008 12:16 pm
pussy
So, I managed to get angry at News 24 again for the shoddy shoddy tabloid style reporting about a science article.

I'm sure you know the one. Apparently, there's a demonstrable correlation between calorific intake at the time of conception and sex of the child.

[BBC News] [Science Daily] [New Scientist] [The Guardian]

The Science

A higher male: female ratio in times of high resources is apparently well known in humans and other mammals. There could be any number of developmental mechanisms for this - conception and implantation is a big fuzzy mystery to me, although the Science Daily articale says that IVF researcher have long known that high levels of glucose can encourage male embryos and inhibit females. However,  It's possible that certain diets affect whether a blastocyst of a particular sex implants or survives. It might also affect the vaginal environment to favour sperm of one sex over the other. 

The evolutionary arguments are more interesting:

Boys are Bigger

You knew this, I'm sure. Sure, there's overlap, but baby boys tend, on the whole, to be bigger than girls. Heavy babies put more of a strain on the mother during pregnancy. If the mother's diet is particularly poor, a high-maintenance pregnancy could have a lower chance of survival, or pose a health risk to the mother. If the body can't cope with gestating a boy, then it could be that rejecting male blastocysts in favour of the chance of a female one next month might improve mother and child's chance of surviving.

Male fitness is more resources-dependant.

This one is related to the Trivers-Willard hypothesis (thanks to Gene Expression for giving me that name). Size and social status generally affects a male's chances of producing offspring more than females, whose fitness is generally limited by other factors. So if a conceiving woman is enjoying a high level of resources, it's worth putting the effort in to produce a healthy, strong male, as a healthy strong female (while better than a small weak child of either sex), would give less of a fitness boost. Meanwhile, if resources are scarce and your child may be less healthy, a small weak daughter would be a better bet than a small weak son.

Women contribute more to general resources than men

OK, I'll throw my hands up and say I more or less made this up on my own - sort of. See, I'm a fan of the Grandmother Hypothesis and the associated models of early modern human behaviour. However, I'm painfully aware my support of this is probably coloured by my political views - but at least I'm up front about it? (Rather than those men who appear to reject it simply because hunting is awesome, yo). In a number of hunter-gatherer societies, the majority of nutrient intake for a family comes from the mothers, infirm-and-elderly and children, who are doing the 'gathering' of high calorific tubors while men are off doing the hunting thing. Yes, meat has a lot of calorific value, but it's usually shared amongst the whole tribe, regardless of who killed it, and therefore a man being a good hunter is more likely to produce a societal benefit (important for humans, yes) rather than a direct health one for his family. But a family with a high number of women collecting food at home and sharing it among families will have a more direct health benefit to fitness. So in times of low-resources, it might be better to invest in a gatherer than a hunter. This, I'm afraid, is much less 'sticky' as an explanation, because it's a time delayed reaction (gender differences in adults won't affect fitness for over a decade after the child is conceived) and because it affects only humans, and doesn't explain the same phenomenon in other mammals. I just wanted to babble about my pet hypothesis.

The Journalism

But the scientific interest is not why I'm writing about it today. I'm writing because once again the popular media and blogsphere are doing it wrong.

Mostly, anyway. This section from the Guardian's report caught my feminist eye:
"We were able to confirm the old wives' tale that eating bananas and sohaving a high potassium intake was associated with having a boy, as wasa high sodium intake. But the old tale about drinking a lot of milk tohave a girl doesn't seem to hold up. In fact, more calcium meant theywere again more likely to have a boy.
I had a conversation a while ago with Bing over 'natural remedies' as a feminist issue. While I despise the bullshit and lies used, not just by 'alternative therapists' to prey on ignorance and turn a buck, but by journalists to tout shit like - well, see below - to sell a paper, I also hate the way "old wives tales" are always dismissed out of hand as automatically being such, because there's no way any knowledge that forms part of a female-based oral history can stand up to the rigours of Big Man Science

 - I'm a part of Big Man Science. I love Big Man Science. I trust Big Man Science to a given extent because I know how it works and what its faults are. I also never ever call it Big Man Science. It's the most reliable system we have for understanding How the World Works. But still, I like to see "folk wisdom" supported by science. It says, to me: Hey, people aren't stupid. We've known this for years. And I like it.

However, BBC News 24 is disgustingly tabloid inna morning. They turned it into a laugh and a joke about how this means eating breakfast when pregnant means you'll have a boy, and trotted out families of 8 sons, and where generally incredibly lax about reporting mechanisms and reasoning, prompting some delightful products of comprehensive  education to write in and say but I thought sperm determined sex. Well, yes, it does. And no one's ever going to say it doesn't, unless the BBC continue to suck so hard at actually supporting the facts about - well, anything.

Then of course, there's the f-word. Oh, the f-word. Sometimes they make we want to pat them on the head and say "OK, anger about misogyny good. Now try directing it at actual misogyny, and not and those poor donkey-lovers. (Uh, fans of donkeys. Not actually 'lovers'.Yes.)

They've decided that the whole thing is anti-woman. Because apparently any understanding of sex ratios and causation is anti-woman and sexist. And - yeah, I think sex selection is sexist, usually misogynistic. I don't need to find stats about female infanticide and selective abortion, do I? That's a problem even in my hometown. And obsessing about the gender of your unborn child is definitely unhealthy and indicative of an enforced gender role for your child. But I refuse to say that we should never investigate natural causes of sex ratio, because it's a phenomenon we deserve to know more about, on account of being there.

They give lip service to actually finding problems with the method ("OMG I want a graaaaaph!") and launch straight into studying natural sex selection implies girls are bad, and will cause child abuse in young girls.

When this is how I find out about nominally interesting scientific research, it's time to fix my reading list.



Apparently LJ-addons doesn't like the way I've formatted the LJ-cuts. View this post in my style, your style, or in light format.
Opinions 
23rd-Apr-2008 12:26 pm (UTC)
Ugh. Just ugh. I have a lot of time for herbal remedies. I would of course subject them to Big Man Science to find out if they actually work, how they acually work, and make it cheaper/purer and generally better.

Tim Clutton-Brock has done a lot of work on deer on the Island of Rum, looking at sex-ratios and environmental factors. Ecology and social rank can skew sex ratios too. If daughters inherit a mothers rank then high-ranking females will have more daughters and low ranking females more sons. I'm sure this has been seen in monkeys. I suspect that might be more important in humans than resource scarcity. But then you might pick it up if you can correct for social status, while not affecting variability of food resources.
23rd-Apr-2008 12:43 pm (UTC)
Well there you go. I wish people didn't feel the need to make this more interesting than it already is, FFS.
23rd-Apr-2008 01:52 pm (UTC)
Have commented over on the Fword. I agree that most deliberate sex selection is misogynistic. You then have to ask yourself why the sex selection is occurring. From the PoV of the family in India trapped in the caste system it makes sense not to have daughters.

But this research isn't looking at deliberate sex selection. Its asking what happens when the body is left to decide for itself which gender of child to favour.
23rd-Apr-2008 12:56 pm (UTC)
Huh, interesting and informative. And reading the whole 'calories make boys' thing makes me glad I took a genetics course in college so I can go "Ahahahaha, no."
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