The headline said it all: doctors who kill. When it emerged that trained medical practitioners were involved in the failed terror attacks in London and Glasgow on 29-30 June 2007, there was near-universal shock in the media, the blogosphere and the workplace in many lands.

A lot of that, as Michel Thieren says in openDemocracy ("'Terror doctors': anatomy of a void concept" , 12 July 2007), was because people - perhaps wrongly, sometimes - believe doctors are pledged to save life. The idea that protectors of life might be perpetrators of death cuts deep.

It is worth emphasising that many uncertainties surround the affair, including the exact responsibility of the individuals associated with or detained on account of it. But from what is publicly known, the "doctors' plot" (another inevitable headline) went further than a marginal breach of the Hippocratic oath. As a science-journalist colleague of mine put it, these people were the offspring of the Enlightenment. Scientists. Our tribe. How could they?

Debora MacKenzie is a science journalist who writes regularly in New Scientist and other publications

The best and the brightest

The question, and the larger collective reaction of which it is part, may reveal as much about the "us" it contains (and our attitudes to knowledge, class and cultural difference) as about the nature of the threat it seeks to identify. But the London-Glasgow events may tell us something about a certain kind of terrorist too, beyond the evident fact that a particular combination of elements (injustice, ideology and political motivation among them) can come together in an individual person's decision to help pack a car with a clumsy heap of propane canisters, petrol and nails and seek to ignite it in public places where hundreds of citizens are gathered.

What is this "something"? The dominant media and popular image of those who take up small arms for a cause is influenced by the experience of nationalist or anti-colonial struggles around the world, which tend to be focused on the control or reclamation of a particular territory. But many of those involved in the new transnational terrorism of al-Qaida and related groups are far from the products of slums or backwoods religious schools: they tend to be well-off, educated people, often with roots in Africa or Asia but who have typically lived - and become radicalised - in the west.

Indeed, the data from a number of sociological studies indicate that university-trained people in scientifically-allied professions such as medicine and engineering punch well above their demographic weight in radical circles. A number of writers, among them Hassan M Fattah (in the International Herald Tribune) have explored this connection in the wake of the British events, continuing a thread of discussion among academics and journalists.

Peter Bergen of the New America Foundation examined the backgrounds of the seventy-nine people behind five major attacks: the World Trade Center attack in New York (1993), the east African embassy bombings (1998), 9/11, Bali (2002), and London (2005). Of the sixty-three whose education was known, two-thirds had been to university, half in the west. Four of the total had, or were working on, doctorates. The largest group had studied engineering; the next most popular field was medicine.

Marc Sageman, a forensic psychiatrist with the Foreign Policy Research Institute and author of Understanding Terror Networks (University of Pennsylvania Press, 2004) studied a sample of 400 al-Qaida operatives. Two-thirds were either professional or semi-professionals; most were trained in science and engineering, whereas few had studied religion or the humanities. They were from well-off families, mentally healthy, "the best and the brightest".

Andrew Bostom of Brown University notes that several leading figures in Hamas as well as al-Qaida have medical backgrounds. The background of prominent members of al-Qaida, and those active in its higher-profile attacks, is interesting in this regard. Osama bin Laden trained as a civil engineer; Ayman al-Zawahiri, his deputy (and by some current accounts rival) practiced as a surgeon. Ramzi Yousef, who led the first World Trade Center bombing, won an electrical-engineering degree in Wales. Almost all the pilots and planners of 9/11 had degrees from western universities, including operational commander Khalid Sheikh Mohammed (engineering, North Carolina) and lead pilot Mohammed Atta (urban planning, Hamburg).

Some analysts note too that the ability to negotiate a loosely-structured (and male-dominated) career path is an adaptive trait in both engineering and medicine. Sandra Bell of the Royal United Services Institute (Rusi) argues that the social status of doctors and engineers makes them ideal targets for recruiters.

Also in openDemocracy on the attacks in London and Glasgow in June 2007:

Sajid Huq, "The car-bomb: terror's globalisation" (6 July 2007)

Tom Gallagher, "Scotland's nationalist-Muslim embrace" (11 July 2007)

Michel Thieren, "'Terror doctors': anatomy of a void concept" (12 July 2007)

The tools of the mind

The Enlightenment inheritance shapes the response to this data: the proposal of hypotheses to explain it. In particular, does scientific training make a person more or less likely to embrace terrorist solutions to perceived wrongs than other members of his group?

Three answers are possible:

• it's irrelevant

• scientific training should actually immunise a person against terrorist sympathies, but like any vaccine, it occasionally fails

•scientific training actually predisposes people to terrorism.

The world is messier than such neat schemas suggest. These might each be valid in varying degrees for different organisations and individuals. But it might be worth thinking through the possible connection in more detail, by elaborating briefly on each hypothesis.

It might be argued, then - the first hypothesis - that education is irrelevant to the whole issue, and that the disproportionate representation of science graduates in the terrorist population is an accident. The people who become active in al-Qaida-style terrorism, after all, are in a tiny minority, so the fact that this sample happened to turn up a larger-than-might-be-expected number of doctors and engineers might be purely random.

The fact that the pattern has repeated itself in different times and places suggests otherwise. But the explanation could be found in covariance rather than cause. It goes like this: bright, capable people in developing societies or from immigrant backgrounds in the rich countries tend - for obvious economic reasons - to make educational choices that will deliver secure, guaranteed jobs, like medicine and engineering (or indeed law). It's settled, suburban kids in the comfortable west who feel they can afford to take philosophy and literature.

Thus a terrorist organisation that seeks (like any ambitious enterprise) such clever, motivated people among its target populations has a high likelihood of finding that they are science graduates.

Marc Sageman argues that terrorism emerges from the solidarity of small bands of alienated, expatriate men, drawn into a spiral of extremist acts (there is an echo here of Mary Douglas's dissection of the dynamics at work among "enclavists"). Many young people - mainly men, and most of them studying technical subjects - have been radicalised in this way while studying in the west.

It is tempting to believe that all these factors - which suggest that scientific training per se is not what attracts a person to terrorism, but which rather add up to co-selection - form at least part of what is going on.

What of the second hypothesis, that scientific training should work against embracing violence, but that this simply fails in some people? Seema Chishti of the Indian Express thinks that while technical training may attract the best and the brightest in developing countries, it fails them by not following through with the spirit as well as the letter of their chosen degree subject.

A technical education has become merely "a tool to get into the job market, make more money", she writes. The educated acquire the tools of technology, but not the Enlightenment thinking that goes with it, acquiring degrees "without imbibing the spirit that is central to modernity - acknowledging the right of all citizens on this planet to coexist". Science has been unable to deliver on its promise to prevent this.

But it is possible to go farther and ask - the third hypothesis - whether a scientific education actually predisposes to terrorist inclinations. The leading scholar of Islamic history and ideas Malise Ruthven argued in openDemocracy soon after 9/11 ("Cultural schizophrenia", 27 September 2001) that there are a disproportionate number of scientifically trained people in fundamentalist movements because they are less critical of "simplistic religious messages", as "technical specialisation tends to discourage critical thinking".

This could be another argument that says more about attitudes to knowledge and class than about the factors that shape terrorist activity. There are certainly different styles of thinking in the "two cultures". But when one's work is subject to the harsh judgement, not just of colleagues but of empirical reality - did the patient live, or the software work? - I would argue that critical thinking is indeed encouraged, if in diverse ways. It would be hard to argue, for example, that doctors and engineers are not at least as hard-nosed and sceptical as, say, sociology majors (see Atul Gawande, Better: A Surgeon's Notes on Performance [Profile, 2007]).

At the same time, it might be expected that medical and engineering people - more than scientific researchers, say - are prepared in given circumstances to take a hands-on attitude and say: listen, we understand this problem, let's do something about it. Such a person might well be more likely to try something desperate but dramatic, the sort of therapeutic intervention doctors tellingly call heroic measures.

But the social, developmental dimension of the issue may be relevant here. Malise Ruthven notes the "schizophrenia" experienced by people who work with scientific principles while living a pre-scientific mindset. Along with other writers (such as Michael Ruse and Karen Armstrong, see fundamentalism as stemming from the severe unease experienced by people making the transition between traditional life based on received authority, communal identity and stability, and modern life based on complexly changing evidence, urban plurality and the notion of progress.

Also in openDemocracy on al-Qaida's progress:

Faisal Devji, "Osama bin Laden's message to the world" (21 December 2005)

James Howarth, "Al-Qaida, globalisation and Islam" (20 January 2006)

Mohammad-Mahmoud Ould Mohamedou, "The dividends of asymmetry: al-Qaida's evolving strategy""Al-Qaida's fresh horizon" (18 December 2006)

Paul Rogers, "Al Qaida's fresh horizon" (5 April 2007)

If these three hypotheses bring any clarity to the problem, what should be done to address it (and under whose authority): more history and philosophy, more ethics and Enlightenment studies for students most vulnerable to the dark glamour of the secret network?

Perhaps. But I would suggest that part of the answer is not less science, but more. In this I mean deep science: not just how to diagnose an infection or debug a programme, but how to think sceptically and still feel one has a confident foundation of belief and identity. Surely people whose lives are not plagued by a pervasive cognitive dissonance between how they work and how they were taught to think are less likely to turn to heroic measures to right wrongs?

In addition, many scientists have reported that contemplation of the stunning complexity of the universe leads to the kind of awe and humility experienced in many religions. This counteracts the hubris of technological power with the realisation that we don't actually understand everything. That must work against the temptation to impose one's beliefs through violence.

Or it should. Plenty of societies that claim to venerate science have gone around imposing precisely that. But then, religious groups that claim to venerate peace make war. People are not perfect, but of the things that conduce to improvement, a proper experience of science. An improper, incomplete experience, however, might well be disorienting enough to be dangerous.