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Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format. New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address. THE LAST WORD Well spotted What causes freckles? And why do some people have them while others don’t? n A freckle corresponds to a higher concentration of the pigment melanin, and is most obvious when it contrasts with fair-coloured skin. Freckles are associated with variants of the gene on chromosome 16 for the melanocortin-1 receptor (MC1R), which are also responsible for red or ginger hair. This probably explains why there is a correlation between freckles and red hair. Melanocytes in the skin produce melanin and package it into organelles called melanosomes. These are passed into overlying keratinocytes, the cells that form the outer barrier of our skin, where they release their payload of melanin. Those born with darker skin have larger melanocytes, which lead to more melanin in the outer skin cells. Freckles are also associated with bigger melanocytes. Freckles are triggered by exposure to sunlight. UVB radiation activates melanocytes to increase melanin production, which can cause freckles to darken, increasing effectiveness as a sunscreen. The person tans relatively quickly where they have freckles, but the skin between is still prone to burning. Red hair and freckles occur most frequently in people with northern or western European ancestry. For example, 13 per cent of Scots are redheads and about 40 per cent of them carry the red- hair gene. Fair skin and freckles might bestow an evolutionary advantage to those living at high latitudes, where it is colder and the intensity of sunlight is lower. It is suggested that a paler complexion reduces heat loss through radiation, though clothing would surely be more effective at retaining heat. The lighter skin pigmentation between freckles also leads to greater absorption of sunlight and higher production of vitamin D, reducing the incidence of rickets in northern latitudes. Mike Follows Willenhall, West Midlands, UK Whiff of mystery When I was young I remember attending soccer and rugby matches at which a player might suffer a knock to the head and pass out. The medical team would then open a small bottle of smelling salts under the player’s nose to bring them round. What were smelling salts and how did they work – if indeed they had a genuine effect? You never hear of people using them today. n Smelling salts are essentially ammonium carbonate crystals, which on contact with water release pungent ammonia gas. The bottle held the reagents in separate compartments and was designed so the crystals would be wetted on opening. The effect is genuine: as the player inhales, the ammonia irritates their nostrils, triggering two physiological responses that help revive them. First, irritation of the nasal lining (and windpipe if deeply inhaled) triggers a sharp intake and exhalation of breath, drawing in more air and increasing oxygenation of the blood. This reflex occurs even when fully unconscious. The irritation also sparks heightened activity of the sympathetic nervous system, raising heart rate and blood pressure, increasing blood flow to the brain. The face-slapping used to revive boxer Rocky Balboa in the Rocky movies similarly worked through irritation. Ammonia is both toxic and corrosive, and above a certain concentration lethal, but smelling salts provide doses well below injurious levels. In sport, they were used not only on the field but also in the boxing ring on knocked-out fighters. Their use was banned by the International Boxing Union in the 1950s and is discouraged by the English Football Association, because an athlete’s outward immediate recovery makes it hard to assess the severity of brain trauma and the risk of ensuing complications, while their recoil on whiffing the salts could exacerbate any upper spine injury – or indeed cause it. Though their use is now rare, smelling salts figure in many a Victorian novel where a lady has swooned on hearing shocking news, and more recently police on the beat in the UK sometimes carried a bottle, just in case. Nowadays when goading someone to wake up, we just tell them to smell the coffee. Len Winokur Leeds, UK This week’s questions HOT IN THE HAY I have always assumed that the belief that haystacks can burst into flames spontaneously was a convenient myth to cover for careless farm workers having a crafty cigarette break while forgetting their surroundings, but a friend insists that it can happen. Surely the only way hay can warm up significantly is if it is wet and bacteria begin to heat the stack as part of the process of biodegradation. But I’d be amazed if this could generate temperatures hotter than about 40 °C. So how else could ignition take place? Antony Wheatley Malaga, Spain NO PIPS TO SQUEAK I have a mandarin tree that produces lots of fruit. Last year some of its fruit had pips but the rest contained none. This year I couldn’t find pips in any of the fruit. What causes these pips to form, or not? Malcolm Frost By email, no address supplied “Ammonia is both toxic and corrosive, and above a certain concentration it is lethal” Last words past and present, plus questions, at last-word.com The new book out now: packed full of wit, knowledge and extraordinary discovery Available from booksellers and at newscientist.com/dolphins Will we ever speak dolphin?
