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The fact that genetic developments linked to higher intelligence have been dated to around the time of a sudden explosion in the making of more complex tools would appear to be more than a coincidence( 18 October, p 6 ). What was required in a tool? How and where it would be used? How it …

I have bipolar disorder. In the modern world, that is often very unhelpful, particularly during hypomanic episodes. However, in a hunter-gatherer society, I could see these episodes having an advantage. You could stay up all night to watch out for danger. Even the hallucinations that come with psychosis may have been seen as important to …

Thank you for Raihan Alam and Tage Rai's excellent article on how society punishes people. The Mendota Juvenile Treatment Center study showed that offenders who received counselling did far better than those who didn't. The science shows that kindness leads to a better outcome for all concerned( 18 October, p 19 ).

Throughout humankind's history, we have had to get used to taking high risks simply in order to eat. If it didn't take risks, the tribe starved. Humanity has evolved to live with risks as a part of normal life. So the idea that criminals are deterred by the fairly low risk of being caught and …

On the main subject of untethering punishment from profit, I think the easiest way to remove any perception of authorities fining people in order to fill financial holes would be to fine them and burn the money. Then the criminal would be punished but the punisher wouldn't profit.

As your article states, it is very likely that will-o'-the-wisps are caused by the ignition of methane or phosphine when bubbles of these merge( 11 October, p 19 ). High-speed propellers and pumps are affected by cavitation when the blades are travelling so fast that bubbles of vapour appear and collapse very rapidly. This violent …

I read with concern that research scientists have developed a stronger, tougher plastic. Why? Plastics contribute massively to greenhouse gas emissions, pollute the oceans and kill wildlife. We should be phasing out plastics, not inventing more( 4 October, p 12 ).

James Wong describes the use of chilli powder to deter wildlife from eating plants in the home garden. I too thought it was a good idea when ring-tailed possums discovered my rhubarb patch. Yet they seemed to enjoy the treat even more. It seems Australian wildlife is tougher than those European wimps. I moved the …

The short article by Caroline Williams about the selective detection of sounds was of particular interest to me as one who depends significantly on hearing aids( 11 October, p 20 ). The problem is that in, say, the dining area of a pub, the aids will selectively home in on what happens to be the …

Vincent Flood, in Illinois, US, pins inordinate faith on geoengineering to keep our planet in a habitable state – partly, it seems, because you can't "tell people in low-income countries they can't have air conditioning or cars...". But people in low-income countries currently aren't the biggest problem. The people who do have to be forced …

Graham Lawton writes about the conspiracy theory that bad actors are using aircraft contrails to poison us. I have experienced the discomfort caused by ham acting in the theatre, but was surprised that bad actors could poison the upper atmosphere as well( 11 October, p 26 ).