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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 )

I've grown up reading my father's copies of Â鶹´«Ã½ , and as a student at the University of Texas at Austin, I have been learning about oceanography and the effects of climate change. I was delighted to read about the youth of the world coming together to combat the detrimental actions that have been …

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 most pleased to see my field of study – Corded Ware culture – featured on your cover. But the mention of genocide and "Stone Age conquerors" is, to my mind, overstating the evidence. Migration is no doubt a factor in the changes observed in the third millennium BC in Europe, but that doesn't …

Some questions sprang to mind about the spread of the livestock herders called the Yamnaya. Where does this name come from? Barras refers to some of the Yamnaya travelling to the Indian subcontinent. Is this perhaps the origin of the Indo-European family of languages? The editor writes: • The name is from "Yamnaya Kultura", a …

Terrance Chapman doesn't know the reason for his mother-in-law's total tooth removal in the 1930s (Letters, 16 March ) and Aroha Mahoney says a neighbour's were removed in the 1950s to save her husband money (Letters, 6 April ). My father, who suffered the same fate in the early 1900s, explained that this treatment was …

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 …

You draw the conclusion that alternative facts are real from a paradox, which arises from a thought experiment about the states of friends of observers of a quantum event ( 2 March, p 7 ). This would only be true if we accepted that an unambiguously quantum object such as a single photon can be …

Geoff Convery suggests that cystic fibrosis carriers might recognise each other through olfaction (Letters, 2 March ). But cystic fibrosis is caused by a mutation in a single gene. It seems extremely unlikely that one mutated gene among tens of thousands would be detectable by smell.

• 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 ).