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What a pity that David Sloan Wilson, who aims to improve lives using evolutionary principles (27 August, p 28) , has not received the press coverage given to Richard Dawkins. For once, someone not only signals positive aspects to evolution, but tries to put them into practice. A board replacing a shop window in Clapham …

Contrary to Andy Bebington's letter ( 13 August , p 30) it is what you do, not what you think, that demonstrates and proves your existence and that of the world around you. What you do may require thought, but thought is a private activity – whereas your actions have a public impact. A public …

Since there is an infinite number of alternative universes (23 July, p 37) , there must be one in which there isn't an infinite number of alternative universes. Perhaps this is it.

Some of your readers have spotted several alarming points about your existential special issue ( 23 July ), including Eric Adams (6 August, p 32) , who noted that the question "How do I know I exist?" makes no sense. The articles follow the convention which allows fantasy tales unconnected with physical reality to count …

You report that the US Court of Appeals for the Federal Circuit overturned a lower court's judgment that human BRCA genes, linked to breast cancer, cannot be patented because they occur in nature (6 August, p 4) . The court reached this decision on the grounds that the genetic sequences patented omit junk DNA – …

You report that antibiotic-resistant bacteria can, in some cases, outcompete the wild-type strain (6 August, p 14) . The "common sense" view was that resistant bacteria should shed the determinants of resistance, for example by losing genes, after removal of antibiotic pressure. It has been questioned before. Take bacterial integrons, which are genetic elements that …

The idea that we stop ageing at 90 is quite convincing (6 August, p 42) . Michael R. Rose also suggests that we are progressively better adapted to a hunter-gatherer diet as we get older, since selection pressures decline after we cease reproduction and our older bodies have not adapted to agriculture in the last …

In his letter on existential issues, Larry Constantine recommends the application of Occam's razor to modern cosmology (13 August, p 30) . While this is a useful tool in cutting away the unnecessary stubble of overloaded explanations, one shouldn't flay away flesh just because it seems hairy in bad lighting. A single universe is very …

In her letter, Helena Telkänranta mentions "rigid rules" being used to prevent AIs harming humans, such as Isaac Asimov's Three Laws of Robotics (20 August, p 30) . These risk invoking the Law of Unintended Consequences, as Jack Williamson pointed out in his "Humanoids" novels. In these, the humanoids did protect humans from harm – …

Fred Pearce, arguing that the west may be falling out of love with the car, says that US car sales have fallen from 11 million in 1985 to 5.5 million in 2009 (13 August, p 26) . But he neglects to mention pick-up trucks, which when included send the total to 11 to 12 million …

Helen Knight's account of alternative burials (13 August, p 44) missed one of the least damaging options, and the way I would like to go. As someone who has eaten fish, studied foraminifera and harnessed the glow of a marine mollusc, I would like to give something back to the oceans. Burial at sea should …

It is such a shame that ethics regulations bar Arhat Abzhanov from hatching his croc-faced chickens (20 August, p 6) . Foxes everywhere are doubtless relieved by this.