climate-change pollutants ( 21 July,

p 15 ). One implication of this is

that driving a car is “greener” than

walking – if you’re a beef-eater,

that is.

Chris Goodall writes in How to

Live a Low-carbon Life: “Driving

a typical UK car for 3 miles adds

about 0.9 kilograms of CO2 to

the atmosphere.” Walking the

3 miles instead would use about

180 calories. You’d need about

100 grams of lean beef to replace

those calories, resulting in

3.6 kilograms of emissions –

four times as much as driving.

London, UK

Despite spite

From Neil Fairweather

Chimpanzees are incapable of

spite, it seems ( 21 July, p 16 ) but

researchers are having difficulty

reconciling this with the idea

that chimps do exhibit altruism

( 30 June, p 10 ). I suggest a simple

explanation: spite is not the “evil

twin that cannot be separated”

from altruism, as researcher Keith

Jensen puts it.

Altruism is the tendency to

do things that benefit others, at

your own expense. Its opposite is

miserliness.

Spite is the tendency to

attempt to harm those who have

benefited in your stead. Surely

its opposite is the tendency to

attempt to help those who have

suffered while you have gained.

Is this not sympathy?

If chimps show sympathy

towards individuals who have

been deprived for their benefit,

but not spite towards those

who have benefited from their

loss, then there might be some

explaining to do.

Risley, Cheshire, UK

What’s a conspiracy?

From Brian Ziegler

I was intrigued by your checklist

for creating the “perfect

conspiracy theory” ( 14 July, p 35 ).

It struck me that this process

has been used to great effect

by the executive branch of the

US government.

Consider the invasion of Iraq.

Saddam Hussein was the big

bad guy. His operations were so

shadowy that they were referred

to as “playing a shell game”. Colin

Powell’s presentation to the

United Nations as Secretary

of State certainly qualifies as

“carefully selected information

that weaves together into a

compelling story”. Iraq’s proposed

nuclear connection to Niger

offered a prime example of what

to do when new evidence conflicts

with your story. Ambassador

Joseph Wilson published an

article that contradicted the

nuclear theory – no uranium had

gone from Niger to Iraq. Life then

became very uncomfortable

indeed for Wilson.

The theory on Iraq keeps

mutating, as does the strategy.

Apparently, if you’re in power

then your plotting should not be

considered a conspiracy.

Elgin, Illinois, US

From Solomon Rubin

You incorrectly asserted that in

the Iran-Contra scandal, the US

“sold arms to its enemy Iran…

to help secure the release of US

hostages taken by Iran”. The

hostages were not taken by

Iran, but rather by Lebanese

groups over which Iran had

some influence.

New York City, US

From Geoff Locke

Patrick Leman assures us that

he is not secretly in the pay of

various western intelligence

agencies.

Well, he would, wouldn’t he?

Stoke-on-Trent, Staffordshire, UK

Megananobucks

From Stephen Dahms,

Alfred E. Mann Foundation for

Biomedical Engineering

Your feature on nanomaterials

and the span of their

possible conformations and

configurations is of great interest

to many who have recently

discovered that they’ve been

nanotechnologists in

biochemists’ clothing for over

three decades ( 14 July, p 38 ).

This is of course modulated

by the discovery of the origin of

the term “nanotechnology” as a

“fundable buzzword” (see Mike

Holderness’s review of the

“brilliantly opportunistic title”

Nanotechnology and Homeland

Security, 18 October 2003, p 53 ).

Santa Clarita, California, US

The kindest cut

From Alethea Drexler

I was dismayed to see neutering

called “the ultimate indignity” in

a printed headline ( 14 July, p 15 ).

I worked for several years as

a veterinary assistant and I can

assure you that neutering and

spaying are not an indignity.

Sterilisation causes no

psychological harm to pets

and prevents both pet

overpopulation and a long

list of debilitating, painful and

expensive health problems.

Veterinarians have enough

trouble convincing pet owners

that they and their dogs will not

be “unmanned” by responsible

neutering, without having them

see the procedure described in

these terms.

Houston, Texas, US

Wonderful coincidence

From Ann Long

I have been following, with not

a little incredulity, the letters

concerning the anthropic

principle, kicked off by Paul

Davies’s article ( 30 June, p 30 ).

And I have thought, as I always do

on encountering such stuff, of a

tale by Douglas Hofstadter, which

I retell as follows.

Once upon a time there was

a muddy puddle. Having been

muddy-puddling about all day,

when evening came she was very,

very tired.

But her luck was in: as she

eased her shoulders down into

the little hollow in the rock,

sighing a contented sigh as she

did so, she marvelled – and not

for the first time – at just how

amazing it was that, right down to

the tiniest indentation, that little

hollow should be exactly the right

shape for her. Truly, it must have

known she was coming.

But then, she was only

a muddy puddle and had,

therefore, only a muddily-puddily

understanding of such things.

Manchester, UK

For the record

● We mangled Christopher Zeeman’s

proof of the infinitude of the primes

( 21 July, p 48 ), as several readers have

pointed out. With our apologies, here

is a better version. Assume there are a

finite number of primes. Multiply them

all together and add 1. Call this number

n. Now n cannot be divided by any

of the primes we started with, so

it must be either a prime itself or a

product of primes not in the original

list. Either way, our assumption that

the number of primes is finite must be

wrong and there must instead be an

infinity of them.

● In an article headed “Popular breast

cancer drug could backfire in rare cases”

we referred to a report in Oncogene,

vol 46, p 4106 ( 7 July, p 18 ). That should

have been Oncogene, vol 26, p 4106 .

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