Murakami quips that “it won’t be a joke to see patients receive a prescription for a comedy video at a pharmacy”. He claims to have identified 23 genes that may respond to a good giggle, many connected with immune response.

Three years ago he tested his hypothesis on people with diabetes, to see whether laughter could influence blood glucose level. On one day he took the 19 patients to “a monotonous lecture (40 minutes) without humorous content”. The next day he took them to a 40-minute comedy show. The patients ate the same meals on both days. Blood glucose levels were lower after the comedy day than after the lecture.

It’s possible, he says, that the physical movement associated with laughter might have helped to break down the glucose, or that the glucose drop was a secondary effect of fluctuating levels of stress hormones (the impact of emotions on stress hormones is fairly well studied). Still, Murakami concludes that the results, published in Diabetes Care, a journal of the American Diabetes Association, “suggest the importance of daily opportunities for laughter in patients with diabetes”.

Only last week a study at the University of Maryland showed that comedies were as instantly beneficial to the heart as a course of statins or a stint in the gym. Volunteers watching funny films saw their arterial blood flow increase; those watching melancholy or distressing films had decreased blood flow.

In the interests of enhancing the wellbeing of Science Notebook readers, I hereby nominate my favourite celluloid therapies. Dumb and Dumber, Jim Carrey’s finest offering, lives up to its title with moronic aplomb. Those seeking comic enlightenment of a vaguely technical kind should try Galaxy Quest, about a bunch of thespians who visit a sci-fi convention and end up in space, or Tim Burton’s sublime Mars Attacks, featuring evil aliens who invade Earth with awesome weaponry and vicious humour (“Nice planet. We’ll take it!”).

• STRESS appears to have another intriguing, largely unexplained, effect on biology: it can affect the gender of offspring. The effect is well-documented in certain bird species, including Japanese quail, which, it was reported last week in Proceedings of the Royal Society B, produce proportionally more daughters when levels of the stress hormone corticosterone are raised.

  Similarly, one accidental by-product of an attempt in New Zealand to conserve the kakapo, a nocturnal flightless parrot, was a skewed sex ratio. Conservationists had been plumping up the birds to keep them fit for breeding, and this calorific comfort resulted, inadvertently, in the birth of twice as many male kakapos as females. When the scientists cut back the food, they report in Biology Letters, the ratio reverted to 50:50. The so-called sex-allocation theory behind this is that generous feeding produces fit mothers who in turn produce fit sons, who proceed to reproduce with abandon. Conversely, unfit mothers may produce sons too weedy to attract a mate. Therefore, in times of hardship, if you want to perpetuate the family line, you’re better off having daughters. You may get fewer grandkids, but at least you’ll get some.

  Human births appear to respond to stress in the same way. One of the best-known researchers in this area is Ralph Catalano, at the University of California, Berkeley, who has published evidence that both the September 11 attacks and the fall of East Germany temporarily pushed down the birth rate of boys. In 1991, after unification, the ratio of boys to girls born in the former East Germany dropped to its lowest since 1946. In the months after September 11, 2001, a higher-than-expected number of male foetuses were miscarried and fewer baby boys born. Professor Catalano has also found that lean economic times spell fewer boys. In tough times, he says, “it’s not in the interest of the herd to have weak males around”.

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