Just imagine. You have read about the Swissair disaster and are about to fly in a plane of the same make. As you leave for the airport, you read a report from a government scientist. He says that, in his opinion, there is "a very real risk" of the same fault occurring in other planes of the type. "If this distinct possibility is true," he goes on, "it would be an emergency."
What on earth do you do? Do you fly anyway, change your flight, or wait for the Government to ground every plane? After all, the man is an official scientist. He has gone public. He purports to know.
Those were the exact words that a member of the Government's bovine Spongiform Encephalopathy Advisory Committee (Seac), Professor Jeffrey Almond, used this week about lamb. You will recall that BSE led to one of the worst outbreaks of mad-politician disease in 1995-97. Nobody today should need warning to be cautious. The outbreak followed a tiny number of cases of human CJD, which had been tenuously linked to BSE in cattle. BSE was caused by polluting cattle feed with infected cow tissue, a practice stopped some years earlier.
Twenty-seven deaths have been attributed to CJD, many fewer than to such food poisons as E. coli or salmonella which we seem to take in our stride. Yet as a result of the resulting hysteria, and with continental farmers eagerly in the van, the beef industry was devastated. Tens of thousands of cattle were fed to power stations and some £5 billion of public money was squandered. The root cause was a group of scientists changing an "inconceivable risk" of contracting CJD from eating beef (in 1995) to a "very small" one (in 1996).
Science terrorism takes the following form. You isolate a small quantity of statistic, attach to it a lengthy fuse of language, and leave it in a public place for a politician to trip over. More disreputable practitioners then telephone a message to the press demanding a large sum of money for "more research", to be deposited in a named university.
Thus Mr Almond this week. He is chairman of the "sheep subcommittee" of Seac, whose former members produced the adjectival high-jinks that led to the 1996 fiasco. This is now being investigated, we hope with due rigour, by Lord Justice Phillips's inquiry. Mr Almond's sheep committee appears to have missed out on a full share of the research gusher unleashed on his "bovine" colleagues during the crisis. Obsessed with mad cows, we forgot about mad sheep, mad goats and other consumable and researchable quadrupeds.
After the BSE scare and as a precautionary measure, Britain (alone in Europe) has banned sheep tissue from the food chain. Seac scientists also checked for BSE in sheep, as distinct from the sheep version called scrapie, but found none. Even at the height of the scare, the risk of any Briton ever catching CJD from beef was put at between one in 50 million and one in a billion, surely the bottom of any Richter scale of danger. In which case, the risk now of catching CJD from sheep which "might" have inherited BSE from some leakage into flocks years ago would defy even the most fantastical risk theorist. Seac had told the Government's Chief Medical Officer that there were "no grounds" for taking action on sheep.
Mr Almond is made of sterner stuff. This week he produced the following logical sequence for Nature magazine, repeated on the BBC. Since BSE has the same symptoms in sheep as scrapie, it would go undetected. Therefore sheep with scrapie, which is harmless to humans, may have BSE, which can possibly transmit harm, without us knowing. Mr Almond's committee investigated nine sheep with scrapie and found no trace of BSE. "But what confidence can we attach to the statement 'BSE is not present in sheep'?" asks Mr Almond. "Absence of evidence is often confused with evidence of absence."
In the circumstance, I would attach total confidence to such a statement. Any layman gazing at a lamb cutlet and wondering if a panic-stricken Cabinet was about to ban it and charge him a further 1p on income tax for the farmers, might even ask a few questions. For instance, what is the point in testing nine sheep, at £30,000 a time, if the test is treated as meaningless? There are 40 million sheep out there. Do we test them all, on so wild an off-chance? Mr Almond asks, suppose just 0.1 per cent of the nation's flock had BSE, it would represent thousands of animals. It would indeed, but this is the oldest of statistician's tricks. Grab from the air an apparently trivial percentage and then reveal it as a huge number. I might as well reply, suppose only 0.000000001 per cent had BSE, then what?
If BSE were to be found in sheep, incants Mr Almond in the face of all the evidence, "that could pose a risk to humans ... we could be facing a potential national emergency". We note the use of conditionals, "if ... could be ... potential". They are chosen like the words of an opposition politician to win publicity yet deflect a charge of scaremongering. Then there is the menacing coda: "I think politicians would have to think very hard about what the appropriate response would be." In other words, pay up or else.
A scientist using such phrases knows what he is about. A "distinct possibility" is converted by headline writers into "Alarm grows over sheep ... Europe to check on lamb safety... More research urgently needed". Nor are other lobbies far behind. The Consumers' Association asks if the Health Department will "consider advising parents not to feed lamb to young children". It thus shifts the burden of a ban on to Government. The introduction of "babes and sucklings" is another familiar twist.
This week's scare brings into disrepute a respectable field of research - into prion proteins in the brain cells of animals - apparently to raise money. It also debases public policy. The BSE fiasco cost British taxpayers more than the Falklands War. Most has gone in compensation to farmers for a pollutant which, in any other industry, would have been financed by a civil suit between victims, farmers and the cattle-feed industry. I am told that £150 million has been paid by the Treasury to the same feed companies whose practices caused the BSE epidemic in the first place. These are vast sums by any reckoning.
In a book out this week called Consiliance, the American scientist Edward O.Wilson calls on his colleagues to seize the high ground from the humanities. Scientists must teach economists, politicians, philosophers, even musicians how to reason, he says. They must boast the new discoveries in behavioural psychology, cultural genetics and brain chemistry. Wilson offers a rollicking good read. But the boot is sometimes on the other foot. When scientists cross into politics they too can get in a terrible mess.
When a scientist peers over his glasses, lowers his voice an octave and intones "I have discovered a risk", how are we supposed to react? We all take risks, every hour of every day. How much risk does this man mean? Why does he not give figures, rather than use vague phrases such as "very small" or "distinct possibility"? The average Briton takes a bigger risk with a single Mediterranean plat du jour than in a lifetime's subjugation to Whitehall's health and safety mafia. Talk of risk is costly mumbo jumbo, designed to make us quake at the feet of Big Science.
Other professions that play fast and loose with public fear are subject to ethical review. Mischievous doctors answer to the General Medical Council, accountants have audit, policemen take sick-leave, politicians get the sack. Scientists can apparently terrify with impunity. Wilson is right. Biology is plunging ever deeper into morality. That plunge is a measure of its importance, ethically controversial and even dangerous: witness the inexcusable attacks by "animal activists" on Colin Blakemore, the current president of the British Association for the Advancement of Science. Such science, and such scientists, must be supported and encouraged.
Yet I cannot believe science really wants politicians or the media to police its ethical frontiers. When scientists go astray, surely they would prefer their peers to hold them to public account. Self-regulation is the measure of a mature profession. Assessing risk in food in recent years has not cast science in a good light. Let science itself set the record straight.
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