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Evolutionary theorist William Hamilton showed that natural selection leads organisms to maximise their "inclusive fitness", not their personal reproductive success. That is, they behave as if they value the lives of relatives, which may lead them to exhibit altruism towards kin. No such principle exists for multilevel selection, as described by David Sloan Wilson (Instant …

Perhaps the playful tone and title of Jonnie Hughes's book On the Origin of Tepees (6 August, p 48) lulled reviewer Jonathan Keats into underestimating the book's ambitious and original discussion of memes. Unlike the vast majority of recent writings about memes, this is a serious book that does "add to the theory" in spite …

Elizabeth Hatherell's discussion of medication problems in children perpetuates a misconception about attention-deficit disorder: she writes that the drugs "numb all feelings" (16 July, p 28) . In fact, people respond differently, and finding the right drug and dose with tolerable side effects takes time. If a child is numbed or "zombied out" by medication, …

In his letter (18 June, p 35) Philip Stewart provided excellent tips for climate change mitigation: reforestation of denuded areas, greater use of timber products, and their reuse and recycling. My calculations have brought me to the same conclusions. However, great care must be taken not to confuse those ideas with similar-sounding ones from forestry …

I congratulate the volunteers on the project Living with Robots and Interactive Companions, who are trying to find out how robots can be truly useful to people – and particularly to "help the elderly with fetching and carrying things around, memory and entertainment" (6 August, p 22) . Many of my relatives have lived well …

Nigel Depledge notes that: "Prior to 1859, the diversity and intricacy of life were often cited as 'evidence' for the existence of God" (23 April, p 29) . Imagine an early man who has just about got language. He's resting on a rock noting a distant tree, silhouetted against the last moments of the setting …

Your article on using a series of columns fixed to the seabed to dissipate wave energy and protect a coastline against tsunamis suggests an alternative concept (4 June, p 14) . A curtain of bubbles can also damp waves. Usually such curtains are generated from compressed air which is piped to the seabed, and they …

Reduce carbon dioxide emissions from shipping by a billion tonnes a year (23 July, p 5) ? No problem. Remove the diesel engines from the world's existing fleet and convert them into galleys. Conscript everybody whose body mass index is too high to pull the oars. Two problems are thus solved in one stroke.

I get frustrated by the discussion of the idea that physical parameters were "fine-tuned" for life (23 July, p 34) . I feel that the people who promote this idea have missed the deep significance of Charles Darwin's thought, and also confuse "life" with "life as we know it". Of course the precise parameters of …

Steve Wilson's comment on the prehistoric brain pondering life, the universe and everything suggests what I always suspected: all of us would be better off going out to do natural history, it's what brains evolved for (21 May, p 24) . Must go. I'm meeting some guys at my local watering hole.

• The reader who alerted Feedback to the startling age of the motor car (6 August, p 64) – "125!" or 10209 years according to a Mercedes-Benz ad – is really named Cooper Jeffrey • The DOI for the paper mentioned in our story about airborne dog faecal bacteria (13 August, p 16) is 10.1128/aem.05498-11 …