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Why is it necessary to take mice up Everest to study any alteration to their erythropoietin levels (31 May, p 7) ? Surely these changes set in at lower altitudes, or could be reproduced using a suitable atmospheric chamber. Might this be a publicity stunt for some mountaineering scientists?

How do cephalopods manage to match their camouflage to their environment so accurately when they can see only green, and do not look at their skin (26 April, p 28) ? A possible answer came to me while reading your article on cuttlefish. To return to a basic tenet of evolutionary theory: biological adaptations arise …

• In the article "Alps are no go without snow" (24 May, p 18) we said the measurement stations are between 200 and 1800 metres above snow level: that should have been above sea level. The study counted snow days, not snowfall; and the 60 per cent decline was for the Swiss plateau between Zurich, …

Hazel Muir laments the fact that few, if any, social policies have been introduced on the basis of valid evidence of benefit, let alone cost-effectiveness (24 May, p 40) . She makes frequent references to the contrast with medicine, in which no procedure or drug is now introduced into clinical practice or public health policy …

The article "Don't expect ET to be like us" (31 May, p 21) covers some of the inadequacies of the SETI programme but does not go far enough. It omits the "magic" factor: as Arthur C. Clarke said: "Any sufficiently advanced technology is indistinguishable from magic." So any communication system used by an advanced civilisation …

The problem of getting people to spend free money hand-outs – like the American rebates Jim Giles discusses in "Single tax rebate won't get US spending" (7 June, p 6) – rather than save them has interested unorthodox economists for some time. None was more unorthodox than Frederick Soddy, winner of the Nobel prize for …

Fred Pearce assumes that the forest land used for palm plantations was cleared primarily for this purpose (31 May, p 6) . However, palm planting is often simply the excuse loggers use to get hold of the land and the rights to log the forest. Such loggers often bribe officials to get the concessions. Frequently, …

Gabriel Bodard objects to health concerns about home-based cellphone base stations being described as a "marketing" problem (26 April, p 20) , but in this case the description is accurate. Femtocells, which only need to reach out a few hundred metres, put out considerably less radio-frequency energy (typically less than 10 milliwatts) than the phone …

William Stanton observed that, as oil is needed to work the farm machinery and natural gas is needed to produce the synthetic fertiliser used in grain production, the phenomena of "peak oil" and "peak gas" will inevitably lead to "peak grain" (31 May, p 23) . The amounts of energy involved are indeed huge: it …

Some perspective is needed on Gregory T. Huang's position that the model developed by neuroscientist Karl Friston approaches a new and "grand theory" of brain function (31 May, p 30) . The brain updating probabilities of what to expect from the world is certainly important – essentially it is the long-discussed phenomenon of learning. But …

Is depression really undertreated (7 June, p 6) ? Adult prescriptions for antidepressants in the US tripled between 1994 and 2005, to 118 million a year, according to the Centers for Disease Control and Prevention. As some antidepressants have been revealed as no more effective than a placebo – but with side effects – who …

Fred Pearce is right to worry about Chinese dams (7 June, p 8) . On a visit to Qinghai prefecture in Tibet over 10 years ago, I saw widespread evidence of a casual approach to dam safety. Some earthen irrigation dams in the highlands relied on weakly cohesive loam cores for their stability instead of …

While it is hard to argue with the principle behind your advocacy of more experimental research on proposed social policies (24 May, p 3) there are formidable practical obstacles. Rigorous research that delivers usable results within the short timescales demanded by policy-makers is hard to achieve. I recently participated in a forum to map out …

Christine Kenneally proposes that it is language that sets us apart from the beasts (24 May, p 28) . I find this odd, since a big-picture view of planet Earth suggests that it is the technical artefacts that we have developed – from stone axes through megacities to rocket ships – that make us outstandingly …