Saturday, January 17, 2009

Evolutionary curveball for curvy?

Anthropological reports can be very subjective and biased, as the Maragaret Mead debacle showed. I would not put much weight on the summary below at all. The conclusions are entirely to be expected from the known anti-Western biases of anthropologists. Any fault may lie with the data she uses rather than with the author herself, however. In one of her papers she quotes one of my papers and agrees with its conclusions! The original article is Waist-to-Hip Ratio across Cultures: Trade-Offs between Androgen- and Estrogen-Dependent Traits" by Elizabeth Cashdan

Having something less than the classic "hourglass" figure may have its benefits after all. While women with curvy figures might enjoy more attention from men in Western culture, and find it easier to become pregnant, new research suggests they may also face some evolutionary disadvantages compared to women with thicker waists.

That's because the same hormones that increase fat around the waist can also make women stronger, more assertive, and more resistant to stress, according to a new study published in the December issue of Current Anthropology. Given those findings, it makes sense that the slim-waisted body has not evolved to become the universal norm, said the study's author, Elizabeth Cashdan, an anthropologist at the University of Utah.

Her study takes aim at a theory popular in evolutionary psychology and medicine: that men universally prefer women with narrow waists and larger hips because their higher levels of estrogen make them more likely to conceive a child, and less vulnerable to chronic diseases. These preferences, the theory goes, have defined women's ideal body shape over time.

The idea took root in the 1990s when psychologists showed men drawings of women's silhouettes and asked them which were most sexy. Researchers found that men gravitated toward images with a waist-to-hip ratio of 0.7 - in other words, with a waist about a third narrower than the hips. Those same hourglass proportions are reportedly shared by stars such as Marilyn Monroe and Jessica Alba, and linked in medical studies with a lower risk of heart disease.

The findings troubled feminists, and drew criticism from anthropologists who said researchers were generalizing about human evolution based on samples of young, mostly white men in industrialized societies. The debate endured for years. "Many of us anthropologists have been in traditional hunter-gatherer societies and most of the women there don't look like that," said Cashdan. "So the question is, if it is adaptive to have that body shape, what's going on?"

In a review of data gathered from cultures as diverse as East African foragers and Chinese immigrants in Britain, Cashdan found that the average waist-to-hip ratio both within and across populations was higher than 0.7. In more egalitarian societies, where women played a greater role in the economy, they also tended to have thicker waists.

That suggests a genetic trade-off, with nature selecting for factors in addition to fertility and attractiveness. One possibility, Cashdan argues, is that extra doses of the stress hormone cortisol and male hormones known as androgens helped our hunter-gatherer foremothers cope in an environment where they had to sidestep poisonous snakes and went to sleep to the serenade of leopards growling. Those same belly-boosting hormones may even help modern women face stressful situations, she says.

More here

Some health myths

WHAT if someone told you turkey doesn't make you tired, or that your nails really don't keep growing after you die? The answer: Check out the British medical journal BMJ, which last month published a list of health myths. It was the journal's second study into health-related myths that even many doctors believe.

Dr Laura Mosqueda, medical director of the UC Irvine Senior Health Centre in the US, said after reading the myths the most important message was not related to the medical beliefs at all: "We are susceptible to believing unproven concepts if they are repeated often enough by 'experts' - be they real, self-perceived or self-proclaimed."

So here are the seven myths:

Drink eight glasses of water each day: The authors found references as early as 1945 suggesting that healthy people should stay hydrated by drinking eight glasses of water each day. But they say there's no evidence supporting that recommendation. Studies also show that most people consume sufficient fluids through daily consumption of juice, milk and even caffeinated drinks.

People use only 10 per cent of their brain: This myth has been around for more than a century. Some believe it came from Albert Einstein, although the authors found no evidence of that. What they did find were studies that show people use much more than 10 per cent of their brains. For example, when almost any area of the brain is damaged, it has "specific and lasting effects on mental, vegetative and behavioral capabilities". Also, imaging studies have found no area of the brain is completely inactive.

Hair and fingernails still grow after death: While it's impossible for the body to continue the complex hormone regulation needed to cause hair and nails to grow after death, this myth does have a basis in a biological phenomenon that sometimes occurs after death. When someone dies, dehydration of the body can cause the skin around the hair or nails to retract, creating the appearance of increased length. But the authors say this is an optical illusion.

Shaving causes your hair to grow back faster, darker or thicker: Several studies show that shaving has no effect on the thickness or rate of new hair growth. But because shaved hair is blunt, and doesn't have the finer taper at the ends of unshaven hair, it can give an impression of being coarse. And new hair sometimes appears darker because it has not yet been lightened by the sun.

Reading in dim light ruins your eyesight: While reading in dim light can cause eye strain, dryness and difficulty focusing, it does not cause permanent damage, the authors say.

Eating turkey makes you especially tired: If turkey contains tryptophan, and science has found tryptophan can cause drowsiness, how is this medical belief a myth? The authors say turkey doesn't contain "an exceptional amount of tryptophan". In fact, turkey, chicken and minced beef contain about the same quantity of amino acid. Other proteins, such as pork or cheese, contain more tryptophan per gram. Perhaps the reason turkey has long been accused of making people extra-sleepy is because of all the over-eating we do at Christmas. Studies show that eating any large meal can make you tired because blood flow and oxygenation to the brain decreases. Plus, meals that are high in protein or carbohydrates can cause sleepiness. So can wine.

Mobile phones cause significant electromagnetic interference in hospitals: Hospitals widely banned mobile phone use after a Wall Street Journal report cited an article detailing more than 100 reports of suspected electromagnetic interference with medical devices before 1993. But an internet search by the study's authors could not find any deaths caused by use of a mobile phone in a hospital.


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