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Rachael Padman describes philosophy as "the experimental study of human nature" (Letters, 5 May ). That's part of psychology. Even moral philosophy is not much about telling people how they should behave: that's religion. These days, most philosophers would say that the philosophy of science in particular is not about answers at all, but about …

Clare Wilson makes the point that we might be focusing on the wrong thing by singling out one particular food group when it comes to our ever-expanding waistlines ( 5 May, p 27 ). Obesity aside, we should also look to the benefits that the sugar tax could offer in reducing tooth decay. This is …

Debora MacKenzie reports research into the relationship between long life and education ( 28 April, p 12 ). The concluding comment is that "Cuba has a higher life expectancy than the US because it is well educated". I would expect the average Cuban to have to take much more exercise throughout life than the average …

Rowan Hooper wishes he could jump back into dreaming sleep ( 24 March, p 32 ). I have found that I can put myself to sleep by filling my lungs through my open mouth and then exhaling slowly and completely through the nose. I breathe that way until I fall asleep. I usually yawn at …

The fact that Clever Hans the horse could read cues from humans is seen as a problem to be avoided in research ( 5 May, p 15 ). Clever Hans's owner, Wilhelm von Osten, clearly believed he had taught Hans to understand mathematics. Psychologist Carl Stumpf, after scientific testing, also believed he had. Then Oskar …

The article on dinosaur taxonomy was very interesting ( 5 May, p 38 ). Can you explain why the sparrow is deemed to have non-bird-like hips? Do the other birds know? The editor writes: • We're so glad you asked. We used sparrows to illustrate all birds, which belong to a branch of lizard-hipped dinosaurs …

Jessica Hamzelou reports a correlation between neuronal size and IQ scores ( 5 May, p 6 ). But, whatever intelligence is, do IQ scores measure it reliably? The format of most IQ tests favours easily measurable qualities such as speed, fine motor skills and the ability to give accurate spoken answers to factual questions. They …

I was interested to read about training quolls to avoid cane toads in order to rerelease them on the Australian mainland ( 5 May, p 10 ). I did wonder, however, what happens when the first generation to be released produce young. Presumably they would need to be trained in turn? You also report Jonathan …

So we have seen a signature of memories in gene activity changes, and it may be possible to create a one-off treatment that would shift a memory's genetic signature from negative to positive ( 14 April, p 6 ). While this is intriguing and the research begs for further examination, I can't help noting that …

Kate Stafford says that bowhead whales can produce two different sounds at once, and "we don't know how they do that" ( 14 April, p 20 ). I wonder whether the whales may be using techniques similar to those used by human throat-singers from Mongolia, Tibet and elsewhere. These singers amplify selected overtones – harmonics …