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Chris Walzer at the US Wildlife Conservation Society is right to be concerned that a ban on wildlife markets in China could drive the trade underground ( 7 March, p 23 ). As Adam Vaughan points out, this occurred when markets were suspended in the aftermath of SARS, and led to further spread of the …

Leah Crane describes the use of three-filter colour combination in Hubble Space Telescope images ( 7 March, p 34 ). They weren't the first to yield astronomical colours using this technique. In particular, there were the superb images that David Malin produced from the 1970s onwards at what was then the Anglo-Australian Observatory. These were …

Michael Bond reports research on what people do when lost in the wild ( 29 February, p 40 ). It strikes me that the way people behave in such situations describes much of the human condition. The untrained human imagination constantly projects our concerns into the future. Since we can't truly predict or control that …

• Disrupting the coronavirus's ability to copy itself can help those with covid-19 because it can stop the virus entering more cells (21 March, p 10).

Thank you to all the staff at Â鶹´«Ã½ for giving us the facts about covid-19. You are amazing. We were travelling in Italy and the Netherlands in February and early March. Language was no barrier to making informed decisions, but the lack of facts was. We were surrounded by misleading anecdotes, biased and unscientific …

Your cover suggests that Steve Haake will tell us whether running or walking is best for your health ( 14 March, p 34 ). His answer seems to be that they are both good, though running can let you take more exercise in a given time. But for a 20-minute jog, say, this doesn't account …

You ask about the relative merits of running and walking. I am 82 years old and consider myself to be reasonably fit. I haven't been to a gym since my schooldays and I don't go running. In my younger days, I cycled to work 12 kilometres each way five days a week and did a …

Besides running and walking, there is a comparatively new kid on the block, namely "Nordic walking". This is walking with poles, derived from Nordic skiing. Like walking and running, it can be practised at various levels. It can also allow people who are elderly or frail to remain active while protecting them from falls. The …

Christel Cederberg and Hayo van der Werf are no doubt right that broad comparisons of the environmental impact of conventional and organic agriculture are prone to be overly simplistic ( 21 March, p 25 ). Both systems operate under rules and regulations designed, in part, to mitigate environmental effects. Organic production adds an additional layer …

Luce Gilmore states that the problem of free will vanishes once it is accepted to be illusory (Letters, 21 March ). Of course it does, and so does any other problem that is treated in the same way. Why don't we declare covid-19 to be illusory? Then we can all go back to normal life.