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Graham Lawton's welcome piece on sports-related concussion recalled for me my earliest days in the UK's National Health Service. In the early 1960s, I began working for a consultant physician who had a much-articulated hobbyhorse concerning brain injury, with particular reference to boxing and to football heading. He advocated as widely as he was able …

Anyone who has looked at the paths of seismic waves from an earthquake will have seen the waves refracted by the increasing densities of the crust, mantle and core. Multiple reflections back and forth are seen to occur, during which the waves repeatedly hit Earth's surface. In various places inside Earth, these waves come to …

I liked your interview with Tali Sharot on habituation and found a lot of sense in it. In particular, it reminded me of how the endless stream of charity adverts on TV, many of which are repeated in graphic detail ad nauseam during the daytime to get repeat payments from senior citizens, can only have …

I read about the plan to bring back the woolly mammoth with dismay. How can anyone theorise about any environmental benefits of such an endeavour without looking at both animal welfare and ecological impact? What would these introduced animals eat? If there isn't enough food, they will starve and lead a miserable life. If there …

I'd say the scale of direct air capture (DAC) of carbon dioxide to deal with climate change must exceed the 80 megatonnes a year in your article. Leaving aside contributions via offsetting, restoring climate stability this century would, at a minimum, involve reducing CO 2 levels in the atmosphere to around 320 ppm. That would …

A solar power station in space would make a potent one that is essentially impossible to defend against . With solar and wind generators spread widely enough on the ground, plus cheap long-term power storage, we don't need space solar.

The idea that wolves could be reintroduced successfully into modern Britain, given today's lack of wild spaces, is laughable. However, should everyone choose to cut their meat and dairy consumption by 90 per cent so that the UK could rewild half its farmland, then wolves probably could be given a new home. I have cut …

New weight-loss treatments all seem to concentrate on making you feel full. For a couple of hours after I wake, despite being hungry, the thought of eating chocolate or cake is very unappealing. Come late morning and for the rest of the day, even when full, I can crave these foods ( 16 March, p …

I was interested in your piece on miso fermentation on the International Space Station. However, I'm not sure any conclusions can be drawn by comparing one jar fermented in space with two on Earth ( 9 March, p 13 ). Different results from two identical preparations fermented in the same facility aren't uncommon, the same …

There is no evidence that an apparent reduction in great white sharks off the south coast of South Africa has resulted in a rise in seal numbers and greater predation of or competition with penguins ( 9 March, p 10 ). The African penguin is in a well-documented catastrophic decline following decades of guano harvesting …