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It is interesting that altruism was used to explain why orcas were apparently offering people gifts. This is based on a human trait, but there is another possible explanation also based on human activity. We frequently offer small edible titbits, usually on the end of a line, with the purpose of securing much larger eatables. …

Your headline "The enemy within" echoes the phrase that UK prime minister Margaret Thatcher used to demonise striking miners in 1984/85. The ruling class planned to crush the National Union of Mineworkers to pave the way for deregulation and privatisation. There was no "invisible rivalry", just open and often brutal class war. Cooperation and solidarity …

You report on home solar being vulnerable to hacks that could derail power grids. My solar installation poses little or no threat as its design limits its output to the grid so that, in the event of there being no demand for its electricity, it will detect this and reduce output appropriately( 12 July, p …

The discovery of wallaby and bandicoot bones on islands near New Guinea and in Indonesia is fascinating. The fact that ancient humans took them there alive implies that seeds of the animals' food plants could have survived in their guts and been deposited on arrival to colonise new land. The presence of disconnected populations of …

I couldn't agree more with Suzanne O'Sullivan that the half-baked UK government plan to screen all newborns for hundreds of gene variants is dangerous, a waste of money and unscientific( 12 July, p 21 ). As well as being pointless from a clinical point of view, as with previous plans to put babies' fingerprints or …

Your description of traces of an isolated population of early humans, never more than a few hundred individuals, has them "scattered over a distance of 1500 km" from Britain to Poland. This is more likely to point to a single, cohesive clan that, over centuries, migrated either east or west over this distance. Such a …

The story on human habitations on Mars that could be built from bioplastics filled me with horror. We have already polluted our own planet with plastics to such an extent that they are found everywhere and in every species. We are now proposing to pollute another world. Not only that, but the algae we end …

From 28 June, p 35

Geoengineering projects are nothing new: mining, coal, oil, etc. have impacts beyond borders and create mounting environmental problems. In the main, these industries are for profit and answer to shareholders. Because of the environmental damage they cause, we may need to consider geoengineering solutions that could have wider impacts too – possibly good, possibly bad. …

Amid debate about the capabilities of artificial intelligence, I asked one about socks going missing in the washing machine. It gave me a reasonable and rational reply. I then asked if the issue could be related to an interaction of relativistic effects of the spinning and electromagnetic oddities of the washing machine. To my surprise, …