Letters archive

Fred Pearce criticises ecological footprint accounting – which shows that humanity is using the equivalent capacity of 1.5 Earths – for underestimating human demand on the planet (23 November, p 28) . Even if Pearce is correct, why would this make the metric "useless nonsense"? Isn't it better to take a conservative approach – like …

The "block" view of time (2 November, p 34) may be a sort of model of the universe as if it were a dead thing (no movement at all). Scientists assume the universe is non-living because physicists study it and inanimate things are what physicists study. There is no good reason for this assumption. Clovelly, …

Further to your coverage of the shift in climate policy after the Australian elections (23 November, p 5) , former Liberal prime minister John Howard recently addressed a conference of climate change sceptics in London and likened people who believed in climate change to "religious zealots". He declared that his gut instinct told him there …

I have to take issue with Mark van Vugt's view on Darwinian economics (23 November, p 30) . I think the analogy between Darwinian evolution of species and the development of businesses and other organisations is most dubious. Businesses can draw ideas from each other, merge, expand, contract, lose bits and change "habitat" and "diet" …

The article on evolutionary economics by Mark van Vugt was interesting, but also slightly disappointing in a way. If the concept of economic activity as "red in tooth and claw" is wrong as the article suggests, then some of us will have to change our way of speaking: when Adam Smith's metaphor of an "invisible …

You reported a slowing in the rate of increase of carbon dioxide production (9 November, p 6) , with a related editorial that hails incremental change and says this is good news for the planet, and that "a global climate pact might be unnecessary after all" (p 3) . As you say, slowing the rate …

Charles Sawyer (30 November, p 33) wonders whether Arkansas is more humane with its method of killing chickens than Ohio is with the execution of death row inmates. Gregory Sams suggests administering morphine (p 33) . Surely we must realise that the years of psychological torture between sentencing and execution render the physical pain of …

Fiona Stewart is pleased that the Mozilla Firefox browser plug-in Lightbeam can highlight third-party sites that snoop on her online activities (23 November, p 34) . To go one step further and block these sites, I would recommend another plug-in: Ghostery. It is free, has versions for all the major browsers, and has lots of …

Your article on school starting age decried the state of early years education in England and went on to say that a similar story applies in the rest of the UK (16 November, p 28) . In Wales, the foundation phase of education for those aged 3 to 7 is based on the principles of …

Of course play has educational value, but the play in day care or preschool is so cocooned it is of limited value. The play at and after school, where young children can interact with and learn from older ones, is far more useful. There is also the question of how long we want education to …

Reading Genevieve von Petzinger's description of the ancient abstract art found in the cave at El Castillo in Spain (23 November, p 36) , I was struck that she could easily be describing medieval coats of arms rather than rock paintings. Perhaps those individual symbols represent clan affiliations, and the divided rectangles a history of …

Your article on prehistoric art starts "All over the world, we're finding art tens of thousands of years older than it should be. What awoke our creative minds so early?" Early compared to what? Why should our minds not have awoken even 1 million years ago? Instead of congratulating our early ancestors on their intelligence, …

Ian Mapleson asks how we should respond if a self-aware robot requests not to be turned off (23 November, p 33) . Surely a more thorny moral dilemma lies in store when a self-aware robot asks to be turned off. Mt Eliza, Victoria, Australia

You conclude that 40 billion sunlike stars in our galaxy have Earth-like planets in their habitable zone (9 November, p 12) . Even assuming each has a single such planet, that is still an impressive number. But if we look at the Earth as an example of the timelines those planets might face, the maximum …

In his letter Martin Savage, discussing how doubling an aircraft's speed from Mach 3 to Mach 6 might affect the rate of fuel use, says it would burn through its fuel in a quarter of the time (30 November, p 33) . The reality is the power needed to propel the aircraft varies with the …

• We fudged the role of insulin in our story on the link between Alzheimer's and diabetes (30 November, p 6) ; we should have said the hormone instructs cells to absorb glucose. • Our claim that 500 tonnes of methane per square kilometre was bubbling up from the Arctic seabed (30 November, p 18) …