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You report a high incidence of twins in a small village in India ( 4 May, p 15 ). If this isn't a statistical anomaly, and if the incidence of identical twins isn't increased, I suspect the involvement of an anti-oestrogenic environmental pollutant. In veterinary practice, decreasing the availability of oestrogen in the hypothalamus, for …

Your article on "living younger" greets the probable arrival of drugs to stay fitter in later life as a win for everyone ( 27 April, p 26 ). With any new technology, it is wise to consider possible outcomes that may not be a benefit to society. One passage caught my eye. "Companies are popping …

I read your article on the origins of language in music, mime and mimicry with interest ( 4 May, p 34 ). Those of us who make things with our hands know the origins of tool-making language and terminology. The first words would have been "Aaargh", then "F@#k"! Some things never change.

Mary Rose criticises my belief that people should panic at the threat of a climate breakdown ( Letters, 18 May ). She objects to "stopgap measures", but, in an emergency, such actions are necessary to prevent the issue worsening. Her preferred approach – prioritising economic growth and hoping for a technological fix – is what …

Keith Oldham discusses how cyclists tend not to be penalised for improper or dazzling lights (The Last Word, 27 April ). I was a lawyer involved in a prosecution for careless driving, where a van driver ran into a stationary cyclist on a busy street at dusk and knocked her into the path of an …

Robert Plomin's observation that genes are more important than parenting in a child's development is hardly new ( 25 May, p 39 ). Judith Rich Harris showed precisely this 20 years ago in her landmark book The Nurture Assumption . She made a convincing case that a child's peer group contributes much more to socialisation …

Plomin's interview brought to mind a counterpoint from a documentary, The Mystery of Murder: A Horizon guide, by Michael Mosley. The programme offered persuasive evidence that high stimulation in the brain's amygdala and genes for low levels of the chemical serotonin are associated with violent behaviour, except when good parenting intervened to provide a happy …

Your article implied that selective schools get better exam results because they admit students who did well in earlier tests. I think Plomin has ignored a key variable: that children are bound to do best in a cohort of similar ability. If you are fascinated by calculus and the rest of the class is struggling …

Your point that methane has less impact as a greenhouse gas than carbon dioxide overall may be true over a timescale of centuries, but given that humanity has only a couple of decades to get its act in order, I would have thought that we need to pay much more attention to the significantly greater …

Paul Bowden asks if every vital software update is an admission of poor design ( Letters, 1 June ). Far more often, software errors are a result of inadequate testing. In the early days of software, testing typically took up 50 per cent of a project's budget. Now, a lot of testing is left to …