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Kate Douglas's article discussing the use and importance of rituals in different types of religion (19 December 2009, p 62) reminded me of a recent paper claiming that the evolution of religion could be intimately related to the cost imposed by religious rituals on the believers who practise them. The paper, by Joe Henrich from …

In his article on gift-giving, Robert Rowland Smith states that the tradition is based on the Christian nativity story describing the gifts given to the baby Jesus by the three wise men (19 December 2009, p 34) . Customs vary from place to place, but originally gifts were often given on 6 December, St Nicholas's …

Dave Boothman notes that factors that could be regarded as strong indicators of intelligence, such as the number of patents awarded and performance at university, do not necessarily correlate well, which leads him to conclude that IQ is not a good measure of intelligence (19 December 2009, p 30) . He is right. Tests of …

Paul Monaghan criticised negative comments about the film Vanishing of the Bees , but his calls for research into the impact of neonicotinoid pesticides on colonies misses the point (12 December 2009, p 29) . While bee health in many countries around the world is indeed very poor, it is not pesticides but the spread …

In his article on the science of slipping, Michael Brooks states: "It's a funny old world, where PhD scientists teach restaurant cleaners how to clean floors" (19 December 2009, p 49) . What is not so funny is the low status and low pay accorded to cleaners everywhere. We would surely see far fewer deaths …

In his letter, Collyn Rivers informed us of his experiences of tame cheetahs, to which Henry Nicholls replied that attempts to breed them in captivity have failed (31 October 2009, p 28) . This is not entirely true. The Taronga Western Plains Zoo in Dubbo, New South Wales, Australia, has bred a number of cheetah …

Arran Frood's article on the use of trepanation to treat dementia (13 June 2009, p 33) made me think back to 2001 when my mother was diagnosed with acute-onset dementia. In a few weeks she went from a balanced, composed lady who looked after herself to a completely uninhibited, unrecognisable woman who at times did …

Your generally well-written piece about the concerns many people have with the Diagnostic and Statistical Manual of Mental Disorders mentions its effect on transgender people (12 December 2009, p 38) . The article is let down in this regard by the use of the phrase "sex-change surgery". Not only is this term often used pejoratively, …

Mark Buchanan's article discussing strategies for selecting staff for promotion mentioned the idea of choosing unsuccessful people so as to ensure that they are not stranded in jobs they cannot perform well (19 December 2009, p 68) . The article implies that this is an unacceptable idea that cannot be implemented, but many of those …

• The correct reference for the study which compared the incidence of heart attacks in London bus drivers and conductors is The Lancet , vol 262, p 1053 (9 January, p 34) .