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Graham Lawton says it is often difficult to discuss biodiversity because of insufficient data ( 28 July, p 28 ). The reasons for this are unclear, but I expect time and money considerations play a role. Could those in need of such data turn to citizen science? This involves members of the public giving such …

You quote UK TV naturalist Chris Packham saying he saw no butterflies over two days in his Hampshire garden. I recently joined a staff member of the Yorkshire Wildlife Trust and another volunteer on a butterfly counting "transect" near my home. It may give Packham hope that we recorded more than 100 butterflies belonging to …

Mick O'Hare asks whether anyone is prepared to vouch for the veracity or otherwise of his three tall tales (Old Scientist, 21 July ). I would direct him to snopes.com , where he will find that the jet-assisted car and exploding cookie dough stories are urban myths, whereas the Rich Bastard incident took place largely …

You quote Luciano Floridi saying there is no such thing as an independent fake-news bot unleashed on the web like some sort of alien life taking root ( 14 July, p 22 ). Does this mean it is impossible, or merely that no one is known to have done it yet? Is it impossible for …

Stephanie Woodcock responds to your review of Edward Bullmore's The Inflamed Mind by suggesting we should consider the role of infection when looking at the link between inflammation and depression (Letters, 28 July ). This prompted me to consider the natural state for humans. Have we adapted to be most healthy when dealing with a …

Woodcock asks for consideration of infection , as well as mental adversity, causing inflammation leading to depression. Bullmore does contend that underlying inflammatory physical conditions could trigger some depression. He suspects too many practitioners look only at psychological stress, rather than a directly physical cause for depression. So he does include infection as a cause …

You mention the somewhat toxic site you have chosen for your head office (Leader, 21 July ). You say that the congestion and air pollution is replicated across the country. It's quite nice where I am. You use authors from all over the world, so why insist on being in London, the dirtiest part of …

Tom Kirkwood points out that 105 is the first age at which the probability of reaching the next birthday falls below 50 per cent and illustrates the odds of living beyond this to the record age of 122 by asking who has ever tossed 17 heads in a row ( 7 July, p 24 ). …

Brian Horton mentions doctors' ties carrying germs (Letters, 28 July ). When I was a medical student in the 1950s, I noticed that gastroenterologists, obstetricians and gynaecologists tended to wear bow ties rather than knotted ties to protect themselves, rather than the patient.

Someone say it: we all know what a tie is. Just look at it sticking up from the top of trousers with a knot on the end. It says "I have a penis so I get to give the orders." I find it laughable that the people who wear them can't see that this is …