Letters archive

Adam Vaughan reports measures we could take to reduce greenhouse gas emissions from transport ( 30 March, p 23 ). As he says, they will not be enough. That's because one thing is missing: panic. Academics and policy wonks are still talking as if we are facing an ordinary problem, like stagnant productivity. We are …

It's not just polar bears breeding with grizzlies: humans also interbred with others Alice Outwater could be more surprised at Homo sapiens interbreeding relatively recently with Denisovans ( 6 April, p 9 )

Colin Barras reports work on the spread of Yamnaya culture from the Eurasian steppes ( 30 March, p 29 ). In the UK, the people who built Stonehenge probably left a genetic legacy. Studies show an influx of DNA from 2450 BC, after which Yamnaya DNA varied from 60 to 100 per cent between individuals. …

I was interested to read about evolution by persistence and its connection to the Gaia hypothesis of a self-regulating planet ( 23 March, p 34 ). It got me thinking about a crucial part of the theory. Gaia doesn't care. There is a danger that some people reading the article will take comfort in the …

Isn't the most remarkable fact about the evolutionary process that, by means of the human brain on this planet, the "universe" is asking questions about its own existence?

You suggest that the absence of infant rabbit bones at Neanderthal sites means that rabbits were hunted individually rather than flushed from burrows ( 16 March, p 20 ). It is also possible that rabbits were raised in captivity and harvested only as adults. I am sure that the Neanderthals were smart enough to cotton …

So a species of caterpillar happily dines on arsenic-loaded leaves ( 16 March, p 20 ). I recall how a suggestion that microbes could substitute arsenic for phosphorus in their biochemistry ( 26 April 2008, p 10 ) caused a mild furore and then rebuttals ( 28 January 2012, p 6 ). Wouldn't such caterpillars …

• However it may be discovered that functional disorders arise, there is no suggestion that it is through conscious thinking ( 6 April, p 28 ). • The philosopher Daniel Dennett popularised the word "sphexish" to describe rigidly-determined behaviours, but did not coin it ( 6 April, p 34 ).

Thank you for the feature on the possibility of selection by persistence ( 23 March, p 34 ). It is true that whenever a system, whether a saucepan of water on a flame or a planet orbiting a star, is agitated by a flux of energy, it is inevitable that structures will form ( 21 …

I am glad that the Gaia hypothesis is being revisited, as it can explain a lot. If the planet is seeking stability, human activities such as rising carbon dioxide levels and pollution of the oceans challenge this. As a result of climate change, we now have floods, fires and the spread of disease, all of …