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Feeling hungry, but aren't tempted to eat? Want instead to start running and keep chugging as long as you can?

In humanity's hungry past, these twinned responses might have been a vital survival instinct for someone needing the strength to flee from famine. But today the same body response might be anorexia nervosa.

This is the radical thesis that evolutionary psychologist Shan Guisinger put forward in a paper recently published in the journal Psychological Review. She describes the failures of psychological and social theories to explain the reason anorexia strikes so many more women than men - a ratio of 10 to 1 is often cited - and the condition's strange features.

"Normal" starvation leads to lethargy, depression and increased hunger. Anorexia leads to food refusal, optimism and hyperactivity. Dr. Guisinger argues that the most likely explanation for this is that the genetics of a certain subset of the female population allowed them to lead their families through hungry times.

"When resources were depleted and the tribe despaired, the anorectic's energy, optimism and grandiosity would mobilize the other members to heroic marches. . . . When a starving tribe reached a new hunting/gathering ground, social pressure exerted by family and friends would in turn have helped the anorectic member(s) to begin eating again," she says.

Over time, evolution would have favoured women carrying genes for famine-fighting anorexia.

To support her thesis, Dr. Guisinger presents a host of human, animal, biochemical and historical evidence, but she concludes with a caution: "Like obesity, AN was useful then and is deadly now."

While clearly not the final word on a complicated subject, her analysis allows one to understand the roots of a condition so widespread that common sense says it must have served some larger good in the human evolutionary past.

In the news

Anyone who has tried to pry a mussel off a rock can appreciate its immense stick-to-itiveness. American chemists have figured out that the key ingredient to its glue is a charged atom of iron. This has immediately raised two possible applications. One is a mussel-like glue for surgeons and the other is a new mussel-removing chemical for the fishing industry.

British researchers have learned that milk does wheat good. Spraying it on can help to cure the plant of mildew disease. One virtue is that there should be no complaints about milk being an environmentally worrying fungicide.

Calcium, the stuff of bones, may also be the master component for the body's directional signals. Researchers from California have found that calcium ions are key components of the process that tells the body left from right and subsequently the side the heart should be located on.

On the Web

A variety of salmon struggling against the current imagery should be used to describe the furor caused by a scientific article last week comparing contaminants in wild and farmed fish.

The amounts were considerably higher in the farmed fish, thus leading some scientists to argue that one should eat wild salmon. Not unreasonable on one level, but it ignores the complaints about how previous human demand for salmon has been decimating the wild stock.

At http://www.worldwildlife.org/oceans/salmon_handout.pdf, the World Wildlife Federation details the damage overfishing has caused Atlantic salmon. They are gone entirely from 309 river systems in Europe and North America and 85 per cent of wild Atlantic populations are listed in the vulnerable, endangered or critical categories.

But the big number is the 600,000 tonnes of farmed Atlantic salmon that was caught in 2000, 300 times the wild harvest.

Assuming an average weight of 2.5 kilograms, this means that 240,000,000 extra wild fish would have to be landed if everyone switched to eating them. That would make the variety extinct in short order.