Letters archive

Garry Hamilton's argument that invasive species could be beneficial to ecosystems pertains more to continents than to islands (15 January, p 34) . The continuing damage to many island ecosystems by human-mediated invaders is enormous. However, effective biosecurity measures can prevent invasions, and this is being successfully achieved all over the world – even in …

I must object to the idea put forward in your feature on climate models that "it is the differences between models that help to ensure predictions are in the right ball park" (15 January, p 38) . Splitting the difference cannot be relied on to give you the right answer. Theories must stand or fall …

There are many interesting parallels between the global financial system and natural ecosystems (22 January, p 6) . It is not entirely surprising, given that financial institutions are able to pass on the information which encodes their operations, are subject to mutation and exist in a milieu which imposes selection pressures – all characteristics required …

You say that Chaser the border collie knows the names of 1022 items, more than any other animal (25 December 2010, p 8) . Koko, a gorilla first studied at the University of Stanford, California, reportedly understands twice as many, and can actually use over 1000. Some humans can use even more.

Given that "poo is a zoo", it seems surprising that the report on the use of faecal transplantation to combat Clostridium difficile infections left out one of the most abundant members of intestinal fauna: the viruses known as bacteriophages (18 December 2010, p 36) . These viruses infect bacteria, and were in fact first identified …

We should not be surprised by the strength of the anti-immunisation lobby ( 15 January, p 46 ). In rich nations, the majority of the population has never seen the diseases that we recommend parents vaccinate their children against. Immunisation has been so effective that diseases such as diphtheria and polio have all but disappeared. …

You suggest that having a fat tummy may shrivel your brain (8 January, p 14) . But an alternative explanation could flip this theory on its head: perhaps the brain changes in obese individuals are the cause of obesity, rather than the result. The editor writes: • The study we reported showed a correlation between …

In "Tales from an alternate Earth", Hazel Muir suggests that if our planet stopped rotating, the oceans would settle in bands around the poles because of the equatorial bulge of the Earth (22 January, p 38) . However, as she correctly points out, the bulge is caused by the Earth's rotation – so with time …

The drinking of "extreme" beers, as discussed by Lizzie Buchen, has interesting historical precedents (25 December 2010, p 60) . Analysis of historic recipes indicates that beers strong in alcohol were also high in bitterness. For instance, the 1903 beer portfolio of Hammond's Brewery in Bradford, UK, covered seven beers ranging from a basic bitter …

Kevin Scott asks if anybody can tell him which is the wrong end of a stick (22 January, p 27) . On a trip to Trim Castle in Ireland, a museum guide informed me that the term "wrong end of the stick" derives from the practice of stirring a dung heap. I don't know if …

I looked into the "P versus NP problem" on Christmas Day (25 December 2010, p 24) , and am happy to confirm that Presents (P) most definitely do not equal No Presents (NP). I claim my $1 million prize.

• We incorrectly stated that Charles Derby was affiliated to the University of Georgia (22 January, p 14) . He is actually based at Georgia State University in Atlanta. • In our feature about pain, we gave David Borsook the wrong job title (22 January, p 34) . He is a neurologist, not a psychiatrist. …