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16 | NewScientist | 13 August 2011 DID shrinking guts and high- energy food help us evolve enormous, powerful brains? The latest round in the row over what’s known as the “expensive tissue hypothesis” says no. But don’t expect that to settle the debate. The hypothesis has it that in order to grow large brains relative to body size, our ancestors had to free up energy from elsewhere – perhaps by switching to rich foods like nuts and meat, which provide more calories and require less energy to break down, or possibly by learning to cook: cooked food also requires less energy to digest. Kari Allen and Richard Kay of Duke University in Durham, North Carolina, turned to New World monkeys to explore the hypothesis. Previous studies offer a wealth of data on the monkeys’ diets and show that their brain Reconstructive surgery is all ears PEOPLE in need of surgery to repair or reconstruct damaged cartilage could soon find help in an unlikely place – their ears. Stem cells from human ears have successfully been grown into chunks of cartilage that could replace the synthetic materials currently used in surgery. Takanori Takebe at Yokohama City University in Japan is the first to confirm that the ear contains a source of stem cells, hidden in tissue called the perichondrium. Takebe’s team removed part of the perichondrium from human ears and injected it into mice. The transplanted cells successfully grew into cartilage, which was still healthy after 10 months (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1109767108). “We are now preparing for the first clinical application [of the technique] in our university hospital,” says Takebe. Your faeces, my furry friend, are blowin’ in the wind GO FOR a bracing winter stroll in a major US city and you will be inhaling more than vehicle fumes. A new study has demonstrated for the first time that during winter most of the airborne bacteria in three large Midwestern cities come from dog faeces. Noah Fierer at the University of Colorado, Boulder, found the high proportions of airborne dog faecal bacteria after analysing samples of winter air from Cleveland, Detroit and Chicago. His team checked the DNA in their samples against reference banks which “barcode” organisms according to their genes. SHANNON STAPLETON/REUTERS IN BRIEF Sacrificial guts and boosted brains size varies greatly from species to species. But when the pair controlled for similarities between related species, they found no correlation between large brains and small guts (Proceedings of the Royal Society B, DOI: 10.1098/ rspb.2011.1311). As Robin Dunbar at the University of Oxford points out: “It is one thing to say that the hypothesis doesn’t apply to New World monkeys, and another to extrapolate that to humans.” They discovered that most of the bacteria they found came from dog faeces by checking the bacterial profiles against reference samples of bugs typically present in soils, leaves and faeces from humans, cows and dogs. In summer, the proportions of bacteria in the air come almost equally from soils, dog faeces and the leaves of trees. But come winter, the trees have shed all their leaves and aerosols from soils are limited by overlying snow or ice, reducing absolute counts of airborne bacteria by about 50 per cent. This means that dog faeces becomes the dominant remaining source. Fierer says that at the relatively low concentrations found – 10,000 bacteria per cubic metre of air sampled – the bugs are unlikely to cause disease (Applied and Environmental Microbiology, DOI: 10.1128/05498-11). USING a “mental abacus” to do complex calculations seems to free mathematics from its usual dependence on language. Michael Frank of Stanford University in California and David Barner at the University of California, San Diego, found that children in India from a mental abacus club can do complex calculations while listening to a story. US undergrads with no mental abacus training find the task almost impossible (Journal of Experimental Psychology, DOI: 10.1037/a0024427). The pair suggests that the story does not interfere with the kids’ ability to do sums because, unlike most of us, they do not use words to process large numbers. Instead, they use their visual systems. Mental abacus does away with words
