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Our climate seems to be changing faster than estimated ( 28 July, p 5 ). The goal of climate policy, set out in the Paris Agreement , is to keep the global average temperature rise well below 2°C. We would be more likely to attain this if we gave more weight to methane as a …

So if I supervise my robot, she can harm another human? Kool. Susan Trexler comments on a suggested law that a robot may not injure a human... unless it is being supervised ( 4 August, p 38 )

Robert Milne discusses the definition of a species (Letters, 30 June ). This was interesting but, counter-intuitively, a species is not a natural concept. It is a human construct, an idea to help categorise and log, an aid to our understanding of the rich variety of life. Its origins are in religious texts and the …

Your interview with Regina Barzilay on her work using artificial intelligence to detect cancer was both interesting and encouraging ( 21 July, p 42 ). When a friend went for a mammogram, it was inspected by a surgeon, who thought it was clear, and by two other members of staff, one of whom was not …

Clare Wilson reports that low levels of the neurotransmitter dopamine are associated with risk-taking ( 21 July, p 10 ). From what I read about risk-taking research, it seems that most is based on money or gambling decisions. This may not be a good choice for behaviour sampling. I, for instance, have been a skydiver, …

You say that the number of people diagnosed with autism has been climbing, leading to claims of an environmental cause, but that the increase is probably down to an expansion in the definition of autism and greater awareness ( 14 July, p 32 ). I'm sure this is true, but I still wonder about another …

I was very disappointed to read Stephen Harris's claims that the work of the "cat killer" in London could all be explained by foxes and road traffic ( 21 July, p 26 ). As someone who has seen the work of all three, I can assure him that it is not that simple. I was …

Fred Pearce observes that hydroelectric dams have fallen out of favour with many environmentalists in recent years ( 23 June, p 36 ). This is partly because they drown habitats, which increases greenhouse gas emissions. They also take up land that could be put to other use. Global warming is causing glaciers to retreat. The …

Colin Barras seems somewhat surprised that primates, including our ancestors, "stumble into the Stone Age by chance" ( 7 July, p 10 ). How else might a species realise the usefulness of stone tools other than by trial and error? Or is he thinking that this cultural leap normally requires the presence of a large, …

• The axis of rotation of Uranus lies close to the plane of its orbit, and by the time it and Neptune formed solid cores it would be too late to gather up a thick atmosphere ( 28 July, p 40 ). • A fairly close shave: the star S2 gets within 20 billion kilometres …