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You highlighted the issues associated with false positives in coronavirus testing regimes ( 26 September, p 8 ). However, false negatives are a much scarier proposition. With a false negative result, infected people can merrily go out into the community spreading the virus. They would believe they are safe and possibly relax mask wearing, social …

Yannis Gourtsoyannis and Anjaneya Bapat rightly point out the risk of bringing potential pathogens back from Venus ( Letters, 10 October ). If these organisms, supposing they exist, are harmless in the disease sense there could still be a danger. Having evolved independently on Venus, it is highly probable they would have very different chemistry …

Complex life couldn't arise anywhere without an equivalent to the "mitochondrial event", the symbiosis between an early single-celled eukaryote and a bacterium to create a more sophisticated organism, as Dan Falk suggests in his look at the chance of finding intelligent life beyond Earth ( 3 October, p 36 ). If Venus has life, this …

The evolution of mitochondria is the obvious chief example of symbiosis in the rise of more complex life, but it isn't the only one. Such events aren't of "mind-boggling improbability". Evolutionary theorist Lynn Margulis proposed that cilia and flagella arose from organisms taking thin spirochaete bacteria on board as endosymbionts. That is controversial, but the …

• The image with our "Doctor's diary" article ( 10 October, p 10 ) showed people queuing for flu vaccines at Hamstreet surgery in Kent, UK, prior to the coronavirus pandemic – hence the absence of face masks and social distancing. • Video game Wasteland 3 , which we reviewed ( 10 October, p 32 …

Sandy Ong's excellent piece on automation and its effects on employment misses one cardinal point ( 10 October, p 44 ). New technology tends to increase inequality, and the bigger the effects of the new tech, the greater the inequality that follows. Unemployment can easily come with more deprivation for many and extreme wealth for …

There are a number of issues raised by your discussion of using gene editing to address agriculture's climate impact ( Leader, 10 October ). The first is the assertion that better breeds are the best way to address climate effects. This is highly debatable. What is clearer is that well-proven agroecological techniques, such as agroforestry, …

The accelerating climate change mentioned in your special report is a surprise to some, but why? Melting ice sheets reflect less solar energy, darker surfaces absorb more heat, previously frozen gases escape while fires and dying vegetation worsen matters ( 17 October, p 34 ). Temperature changes also lag behind changes in total greenhouse gas …

Your article continues the head-in-the-sand approach of virtually all publications. The pandemic and global warming are just two manifestations of the real problem: overpopulation. As our numbers continue their out-of-control growth and the attendant problems get ever worse, I ponder: are people really this stupid? The editor writes: See page 36 for economists' take on …

Eddy Keming Chen has me fascinated with his thoughts about vagueness in fundamental physical laws, and the possibility that we may never be able to completely capture the objective order of the universe through mathematics ( 5 September, p 36 ). Clearly, the laws of the universe existed long before we started measuring them. The …