Letters archive

Clare Wilson suggests that screening for breast cancer may do more harm than good (15 November, p 14) . It is not the screening that does the harm, but what is done with the information gained from it. If a group of women who are screened have worse health outcomes on average than those who …

• No one proposes that we stop screening entirely. Unfortunately we lack reliable methods of discriminating aggressive tumours from others – and, if such methods existed, women diagnosed with non-aggressive tumours would need to have quite remarkable confidence in them.

In reply to Adrian Ellis's letter, you comment that the development of an industrial civilisation might be predicated on a "critical mass of people" (15 November, p 30) .This reminded me of a New Scientist interview with David Suzuki in which he was asked how many people our planet could support (15 October 2008, p …

Tim Ratcliffe's vision of stopping investment in fossil fuels and artificially imposing a transition to a low-carbon economy would have downsides (15 November, p 26) . It might slow the growth of knowledge, delay discoveries and lead to greater overall damage to the climate. Fossil fuels can be both the cause of and solution to …

Paul Younger seems to base his opposition to divesting from fossil fuels on a fundamental misunderstanding. He repeats the error that the divestment movement is "premised on the idea that fossil fuels can be abandoned immediately". This is simply not the case. The spearhead of the divestment campaign, 350.org , calls for a wind-down period …

Brilliant, another way to kill each other, with autonomous robots (15 November, p 38) . But they can't be too effective as that would be wrong. What makes a robot that is good at killing people illegal and amoral, but a robot that is less effective but still manages sometimes fine? Why don't countries hold …

David Sanderson points out that farm machinery uses a lot of oil (22 November, p 34) . I read of a solution to this in Meccano Magazine – standard reading for the technically aware schoolboy of the 1950s. It was to provide electric power by overhead cable to the corners of fields. The electricity would …

Petros Sekeris may have chosen an unfortunate example to illustrate his hypothesis about violent responses to resource depletion (22 November, p 30) . Jared Diamond's analysis of events on Easter Island is open to question. There is a case to be made that, despite depletion of many resources, Easter Islanders had managed to create and …

I suspect that the key question about a multiverse (27 September, p 32) is not whether multiple universes exist, but whether the difference between them is as small as the spin state of a single electron – or so great that mathematics itself is useful only in ours, and does not apply in others. (Or, …

Paul Marks refers to a TV drama in which a fictional character is killed by hacking into their pacemaker (8 November, p 19) . He then explains how security experts are engaged in making it harder to reprogram medical devices, just in case anyone should want to do this for real. In the real world, …

Your leader on the moral implications of homosexuality being partly or largely biologically determined did not address one counterargument (22 November, p 5) . There are other desires or traits that are, in all probability, largely biologically determined but which no modern society can tolerate. Why should societies forbid the practice of some desires but …

Andy Coghlan reports a study of gay brothers that provides further strong support for the genetic basis of homosexuality. (22 November, p 11) . There are, however, two counterarguments to be addressed before it can be accepted. The first is that any gene that reduces the chance of the person carrying it reproducing should, over …

• Something else that we didn't have space to mention is that "gay gene" carriers in both sexes have another trait in common: they are strongly attractive to men (23 August 2008, p 7) . Walking and running

I find it hard to believe your assertion that running and walking at 6 kilometres an hour both burn the same number of calories, while dispelling myths about fat (15 November, p 32) . My intuition forces me to think that there must be a difference in energy expenditure of two such different modes of …

• The answer does seem to be different at different speeds. We will return to this.

Helen Thomson writes of a man who has a delusional belief his wife is an impostor, because the emotional processing in his brain does not match his visual processing (8 November, p 12) . This dramatic and moving example illustrates the irresistible triumph of emotion over the insurmountable evidence of the senses. It is frightening …

The article discussing the possibility of generating energy using small-scale nuclear fusion suggested that both deuterium and tritium are stable isotopes of hydrogen. Although deuterium is a stable isotope, tritium certainly is not (8 November, p 9) . It is a low-energy beta emitter with a half-life of 12.3 years. It decays to helium. Further, …

• We got the name of one of the two founders of the Bill and Melinda Gates Foundation wrong (25 October, p 40) . Sorry. • We should have credited the launch of the OpenWorm project on Kickstarter to the community of researchers at openworm.org including Stephen Larson (29 November, p 21) . Independent researcher …