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Michael Brooks, considering the question "How do I know I exist?" highlights the reductionist but irrefutable logic of philosopher René Descartes's famous statement in 1644 that "I think, therefore I am" (23 July, p 36) . All existence may be a delusion except the conscious awareness that one is thinking, whether deluded or not. Whether …

I read with relish David Sloan Wilson's article describing a revival of group selection (Instant Expert, 6 August) . In my university days this went against the received wisdom: I am glad it has finally got its due appreciation. Could the closing remarks, suggesting that the purpose of morality is to suppress intra-group selection, be …

Michael Rose would like to test his hypothesis about ageing and diet by studying people in Papua New Guinea (6 August, p 42) . He believes they were first exposed to agricultural foods in the past hundred years or so. In fact, excavations at the Kuk swamp in the western highlands suggest that this was …

Your report that "women in the US are to be offered free birth control" (6 August, p 4) was incomplete to the point of being completely misleading. Yes, a new mandate now means that contraception will be free... only for those with health insurance. Unlike every other industrialised country, health insurance in the US remains …

Why are you still printing letters repeating old falsehoods about incandescent bulbs (13 August, p 31) ? In many buildings the heat generated from lighting is unwelcome, and expensive to remove if air conditioning is used. Heat from outdoor lighting is entirely wasted. From Robin Trow The electricity consumed by a 100-watt incandescent light will …

Dmitry Belyaev did not only work on aggression in rats (13 August, p 24) . His experiments in Siberia also included foxes, which, in a mere 20 years of selective breeding became dog-like in temperament, actively seeking human company, in contrast to their wild ancestors (3 October 2009, p 40) . Belyaev was effectively exiled …

You report on the redefinition by the International Union of Pure and Applied Chemistry (IUPAC) of hydrogen bond participants to include hydrogen bonded to carbon (30 July, p 9) . Such hydrogen bonds have been recognised since the early 1960s. In 1974 Melvin Joesten and Lawrence Schaad listed over 100 examples of hydrogen bonds with …

Regeneration of the lens of the eye in newts (16 July, p 15) is biologically sensational. What happened to a gecko in Namibia during the second world war was less so, though more dramatic. Two German geologists made off into the desert to avoid being imprisoned. They took their vehicle, as much petrol as they …

Your fascinating article on the use of data mining, in particular to predict weekly Â鶹´«Ã½ sales based on the cover design, missed an obvious trick (13 August, p 40) . As Feedback has pointed out, it was well known in your office that sales would peak if the word "quantum" appeared on the cover, …

In reporting the discovery of the new satellite of Pluto (30 July, p 14) , there is no need to state that it "has been dubbed P4". It already has an official provisional designation from the International Astronomical Union: S/2011 P 1. The use of nicknames is, unfortunately, common. Also, a name cannot be assigned …

The discovery that people born paraplegic dream of walking, and the deaf of talking, as if these were ordinary everyday activities is not surprising (13 August, p 6) . I have in the course of dreams done the usual flying, spoken languages I don't know, and breathed under water; but also swum through the Earth's …

• In "Autism in families" (20 August, p 5) , we apologise if we gave the impression that Rosa Hoekstra of the Open University favoured an environmental explanation for siblings sharing autistic behaviours. In fact, she believes that the study reported in the story strongly reinforces a genetic explanation for autism. • An editing error …