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Clare Wilson reports a test of people's responses to the philosophical "trolley problem", now prominent as a way to probe opinions on who a self-driving car should save ( 19 May, p 14 ). There are reasons to be cautious about any interpretation of the results. As Wilson notes, a problem with this test – …

Alice Klein says Neanderthals and Denisovans seemingly did not develop the same level of intelligence as us ( 9 June, p 6 ). But Neanderthal brains were somewhat larger than those of Homo sapiens , and we are reminded in the same issue that there is a subtle relationship between brain size and intelligence ( …

Peter Fairley discusses the possibility of 100 per cent renewable energy ( 9 June, p 26 ). This throws up at least a couple more considerations we will have to face in the future. What effects on animal and human biology will there be from long-range super-high-voltage direct current transmission from sites where green energy …

Surely it is not so much a question of whether we can get all our energy from renewable sources , but that we must. The only point to debate is how quickly. It seems likely to me that production of hydrogen fuel using electricity to split water will be a major part of this process. …

Timothy Revell discusses holding artificial intelligence to account and European Union citizens getting the right to an explanation of AI decisions ( 14 April, p 40 ). Should software not be able to say "I don't know"? I worked on an AI system for use during anaesthesia. We needed to detect one of two states: …

The condemnation of "smart" electricity meters continues . As with all technology, there is nothing wrong with smart meters in their own right; what is important is how they are used. The use of electricity has changed from being a luxury available to a few rich people just 100 years ago to much of the …

Peter Fairley mentions storing energy by converting surplus electricity into hydrogen by using it to split water ( 9 June, p 26 ). This also produces oxygen. If this were used to replace air in engines, their thermodynamic efficiency could be improved, as the burning temperature of the fuel increases and it no longer has …

You speak of "renewable energy" . I prefer to call it "owned power". If you buy a diesel generator, then you have to keep buying fuel: fuel-based energy is "rented power". When you buy a solar panel, you own a flow of electrical power. It is better to own than to rent, for independence and …

Michael Le Page mentions the genetically modified Flavr Savr tomato ( 26 May, p 28 ). This was a commercial failure because it was never sold to the public except in tins or as tomato paste , making pointless its quality of keeping for three weeks after ripening.

Your excellent article on a new wave of healthier genetically modified foods missed one connection. Paste made from Flavr Savr GM tomatoes launched in 1994 was clearly labelled as GM and was outselling the traditional product. It seems to me that what brought things to a grinding halt was the cattle disease BSE and its …