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I am not sure why Graham Lawton thinks population growth is a taboo subject ( 25 May, p 24 ). I have recently read three books that discuss it and it would seem overpopulation is a battle that is mostly won. A great deal of the world already has a fertility rate at, or below, …

Ruby Prosser Scully continues a story that has rumbled through the pages of Â鶹´«Ã½ for the past couple of years, lending hope that ageing could be delayed by transfusions of young blood ( 8 June, p 7 ). Having been a regular blood donor for 45 years, I observe that the majority of donors …

I commend your article on the European Parliamentary elections for flagging up the fear of higher environmental taxes, which could only make life disproportionately harder for poorer people ( 25 May, p 23 ). It may fuel populism and encourage the idea that environmentalists are part of an elite. The carbon fee and dividend scheme …

I just read your feature about Earth's rubber supply ( 18 May, p 44 ). As someone with allergies to latex and the accelerators used in rubber production (carba mix and thiuram mix), the prospect of a world without rubber seems fantastic. I think this should serve as a wake-up call that we have, yet …

So Deepmind's artificial intelligence can't add up ( 13 April, p 12 ). That reminds me of the late, great Stanislaw Lem, who foresaw this more than 50 years ago in his short story Trurl's Machine . The eponymous inventor creates an eight-storey thinking machine that, when asked to calculate two plus two, thinks for …

I would like to challenge the view of mathematics presented in Peter Bennett's letter on the topic of free will ( Letters, 25 May ). He seems to think that mathematics can only deal with problems that can be described in either a simplistic deterministic way or as the result of entirely random events. He …

Continuing the debate on free will that regularly features in Â鶹´«Ã½ these days, I am concerned that the scientific costs of this discourse are rising exponentially as more scientists pick a side. I realise that doing science also requires discussion, so that we might progress by such means as well as through experiment and …

I read your headline "Chinese rover unearths moon's deeper secrets", and I suspect we are being trolled ( 25 May, p 16 ). Surely the proper verb would be "unmoons".

I was interested to read Clare Wilson's report on the number of twins in Kodinhi in India ( 4 May, p 15 ). She quotes Tim Spector at King's College London, who suggests that a possible explanation could be better medical care increasing the chances of twins surviving. But what is causing the increase in …

You report that 64.9 per cent of drugs tested were broken down by at least one strain of gut bacteria ( 8 June, p 12 ). To minimise this, drugs shouldn't enter the gut directly. Some can be absorbed from the mouth, either under the tongue or through the buccal (cheek) mucosa. Many of these …