Letters archive

In my experience of memory retention, it seems that, at the time this occurs, the brain – consciously or unconsciously – places a memory into a category with a rating of importance varying from "retention essential" to "almost discardable". Memories in the top category can be retained almost indefinitely, while those in the lowest, although …

If thinking hard doesn't cause the brain to consume more energy, it doesn't make evolutionary sense that stress hormone levels rise when we need to concentrate. It is well known that elite chess players lose weight during tournaments . Even though the brain is only responsible for a small percentage of the extra calories burned, …

Jeffrey Lapides has discovered microbes in the brain seemingly implicated in Alzheimer's disease, an unexpected finding. Will this, and similar discoveries, signal a rethink about neurological and mental illnesses? Suspicions must arise that, overall, this may not be a benign microbiome, especially if pathogens are entering the brain. We have medicines that act on some …

Your look at cannibalism mentioned that over the course of history, the practice "has been surprisingly common". In fact, this shouldn't be surprising at all. Cannibalism solves the food shortage problem and is environmentally friendly. So why not? The real question should be: why did cannibalism all but vanish from the culture of Homo sapiens …

Meat is the most "ultra-processed food". It is ultimately plants that have been chewed, digested, broken down, chemically altered, restructured as animal flesh, slaughtered, skinned, butchered and processed even further. Any factory processing of plant-based foods pales in comparison ( 24 February, p 21 ).

Dismissing concerns over ultra-processed food isn't so simple. We can't rely on cravings and appetite for health if we eat stuff that tells our body, by flavour and texture, that it has one nutritional profile while delivering an utterly different one. And what about the removal of essential and beneficial micronutrients when, for example, maize …

The gains from flitting between foraged food sources may not have promoted what we call ADHD. Instead, look at birds feeding on the ground. They don't hang around to pick up the food for a long time, but make frequent, random movements away to different places. This makes it harder for a stealthy predator to …

James Dinneen's review of A City On Mars was interesting. As its authors say, there has been, to our knowledge, no documented human sexual activity in space. However, given our species' predilections, I would be surprised if, with the person-hours racked up on past and present space stations, not to mention lunar and other orbital …

Here is a commercial application of dream engineering that I would welcome. Many people experience leg cramps at night, incidents where, in the middle of sleep, your leg turns into stone. It is very painful. Dream engineering might be able to implant the suggestion that our legs should remain relaxed during sleep. People would pay …

To find evidence to back string theory, Joseph Conlon suggests looking for certain primordial gravitational waves from very early in the universe. Presumably, these would be stretched as the universe expands, just as light waves are. Radiation we see as the cosmic microwave background was stretched many, many times from its original form . Gravitational …

I read your story on making jet fuel from carbon dioxide and it struck me that for this to succeed commercially, all it needs is a place that can generate lots of clean energy, has capital to invest in the infrastructure and has a need to replace an oil-dependent economy. I hope it really is …