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So you think you're unique (24 May, p 28) ? Of course we are – every species is unique – but nowadays we are continually being reminded that we are nevertheless "not so special". It's a coded phrase designed to convey the idea that nearly all the traits distinguishing Homo sapiens from our nearest relatives …

According to Lawrence Krauss, the world is becoming increasingly free of barriers to flows in trade and capital, and for this phenomenon he uses the term "flat" (24 May, p 48) . Ongoing changes to global intellectual property rights, international harmonisation of safety rules, and World Trade Organization agreements are indeed making it increasingly easy …

In your report "Spot the killer" you state that "because Medicare only covers elderly citizens, Sentinel won't identify the side effects of drugs taken by young people, such as contraceptives" (31 May, p 6) . In fact, the Sentinel initiative will also query databases of private health plans that volunteer to participate. These plans cover …

Laura Spinney describes ostrich wings as "spectacularly de trop" (17 May, p 42) . I have kept ostriches for 18 years and can testify otherwise. When it is hot, they raise their wings to expose their bare upper legs to any cooling breeze; when it is cold, they lower the wings to keep their legs …

Thanks to Susan Greenfield for pointing out that brain connections form in response to experience, and that personality and identity might be largely shaped by the nature of that experience (17 May, p 48) . Neil Postman makes a similar point in his book Amusing Ourselves to Death , in which he points out that …

I don't think any serious consideration of the possibility of contacting extraterrestrial intelligences can rule out Steven J. Dick's scenario that they could be a type of artificial intelligence far in advance of our capabilities (31 May, p 21) . But these could only have arisen from the work of intelligent biological entities similar to …

Working on solutions that can meet some people's aspirations, as David Sandilands suggests (31 May, p 23) , is surely a lower priority than meeting all people's basic needs. When everyone has something – anything – to eat is when we can address aspirations of the affluent few for meat. When everyone has somewhere to …

Sprinkling the oceans with powdered limestone (17 May, p 16) is at least a basis for possible remedial action to reduce atmospheric carbon dioxide. It would surely be better to pump a saturated solution of dissolved limestone into the sea rather than dropping a solid, which would require large ships capable of carrying huge amounts …

I am an anaesthetist, so cannot criticise your article "Blood doesn't always save lives" (26 April, p 8) as thoroughly as haematologists will, but its section on "Bloodless surgery" did not give me confidence. Following blood loss during surgery, putting the patient in a hyperbaric chamber will not "load their remaining red cells with oxygen". …

I am the only reader of Â鶹´«Ã½ among my family and friends, and so I manage to amuse them now and then by giving short lectures on the interesting things I read. However, it worries me that I am unsure of the correct pronunciation of some uncommon words. For example, is "oxytocin" oxy-toe-sin or …

Lawrence Krauss's plea for his daughter's friends to turn from managing wealth to creating it (24 May, p 48) poses a stark contrast between investment banking and basic science. However, there is a partial solution to the "overdependence on wealth management" that he rightly deplores. Those who initially choose to create knowledge through basic scientific …