Christmas brings with it the ultimate suspension of disbelief: a virgin birth of the Son of God. And a lack of substantial evidence to back up this claim seems to be no barrier to the belief of millions of Christians.
But when it comes to asking leading lights of science and medicine how they square belief with scientific fact, you might imagine a different story.
Body&Soul asked leading experts in their fields: “What do you believe to be true even though you cannot prove it?” The answers reveal unsubstantiated, but nevertheless influential, theories from yodelling ancestors to winning formulas for artistic achievement.
Belief appears to motivate even the most rigorously scientific minds. It stimulates and challenges, it tricks us into holding things to be true against our better judgment, and, like scepticism — its opposite — it serves a function in science that is playful as well as thought-provoking.
I believe that I have free will over the decisions I make, but I can’t prove it because all the scientific evidence is to the contrary. Like everyone else, I deceive myself that I have it. This is because human beings are designed to think that they have freedom over their actions. In fact, our brain makes decisions before making us conscious we have made them. For instance, the part of the brain that controls movement is active up to one second before we are aware of deciding to move. Afterwards, another part of the brain provides an explanation of why the movement was made. So, although I am able to rationalise why I did something after the event, my brain is always one step ahead.
I believe but I cannot prove that the first song ever sung by a human being was a yodel, a song relying on the voice fluctuating from falsetto to normal pitch.
My latest project is attempting to reconstruct the history of human song with the help of the musician Brian Eno. Our starting point is that songs — from polyrhythmic chants of Xhosa farmers to the nasal cries of Lisbon fadistas — contain information that tells us how humans migrated from Africa more than 60,000 years ago and constructed the diverse cultural world we see today. I believe that songs are the product of a history that can be retrieved if you listen to them. I ’m trying to understand songs as geneticists understand genes or linguists interpret language. If these very different human attributes are ruled by Darwinian dynamics, might not music be, too?
Perhaps. But a yodel as the first human song? The idea seems absurd. But the yodel is not only found among Swiss goat herders; it can also be heard in Congo’s jungles and the Kalahari desert, in the songs of the Mbuti pygmies and San Bushmen. It is among these peoples that I suspect the origin of human song may be found. Of course, I can prove none of this — yet.
I believe but I cannot prove that religiousness is, in part, genetically determined. The strongest reason for my belief is provided by the study of twins by the behavioural geneticist Thomas Bouchard in the 1980s. It gave insight into which aspects of the human condition are nature and which nurture. But I don’t think genes are the only contributing factor. Bouchard’s study, and recent research by psychologists, shows that religious background and parental influence provide environmental influences; in other words, extrinsic religiosity, based on the rewards of churchgoing, such as a sense of belonging. Intrinsic religiosity is a deeper feeling of spirituality, not related to churchgoing. This, I believe, is genetically determined. This belief neither denies nor proves the existence of God. For all we know, it was God who put the genes there.
Professor of reproductive medicine
I believe that life does not begin at conception, but I have no proof. I am an atheist and I believe in the sanctity of life but not that there is a higher spirit up there creating it. I don’t think there is a magic moment when life begins. I favour a gradualist approach. Once a baby is born, it is an individual. But there’s a time before that when it is still part of the woman who is carrying it. At the very early stages of pregnancy, she has the right to make decisions about it. As the pregnancy develops, the growing infant acquires its independent rights.
While I respect the value of a fertilised egg because it has the capacity to create a baby, I do not look on it in the same way that I would regard a child. Life should be respected differently at different stages. A fertilised egg is not a life; it is a potential life. I can’t prove this, but my work is based on it. If I felt that every fertilised egg that I created for IVF was an individual person, I couldn’t do my job. We create hundreds of embryos every week; eight to ten for each person, only ever using two.
I believe but I cannot prove that the biological basis of our individuality is not knowable. My theory is that the unique form, mind and behaviour of each one of us is due to net- works of interaction between our estimated 25,000 genes.
This process is highly particular and utterly unpredictable. Even if we were given a print out of the structure of our genes at conception, we would not be able to say how they would connect in the making of an individual, despite much hype to the contrary.
Our development is not hardwired. A single gene, even one related to genetic diseases, has no meaning outside the context of its networks with hundreds of other genes. So, my belief is that there is no fixed or natural link between genes and traits. This gives a unique take on what it means to be human; when Samuel Beckett wrote “I alone am man” he was right.
Editor of The Edge, a scientific debate website
I believe but I cannot prove that we are moving towards a future full of correct answers but this may cause us to lose our ability to ask the right questions. In this age of “search culture”, with Google and other search engines leading us towards unlimited information, we focus on knowing, on ideas of truth and proof.
Many people welcome these technological advances as the first steps toward a universal library. My concern is that we are moving forward blinded by a naive sense of certainty.
When I asked this same question about belief and proof as the annual Edge question (www.edge.org ), last year, the responses pointed to the new ways of understanding the world: advances in physics, information technology, genetics and neurobiology. But the researchers behind these new developments did not achieve success by having answers: they asked the right questions.
Neuroscientist and pharmacologist
I believe in the final triumph of the good guy. It’s totally unprovable and sounds awfully moral, but it drives me. I think being honest and kind, and living by your principles, wins through in the end, even if it doesn’t seem expedient at the time. This challenges the notion that human beings are corrupt and inherently nasty, committed only to furthering their own causes by realpolitik.
It has led me to consider what a belief is and why people hold them, sometimes even die for them, without any proof.
But belief can obstruct science; it can prevent you examining the evidence properly. Think of how men have argued over the centuries that women are less intellectually capable than men. However, it can also guide you towards an idea. Giving in to a hunch can be the best thing a scientist can do; we shouldn’t underestimate the power of intuition.
SIR ARNOLD WOLFENDALE
Former Astronomer Royal
I believe but I cannot prove that God exists. As a scientist as well as a Christian, I know that I am supposed to require firm knowledge for every phenomenon in which I believe, but with religious belief, the potential benefits are great enough for normal critical attitudes to be suspended. All this is not to say that I accept all of Christianity lock, stock and barrel. Indeed, I hope that it evolves, as some of the Christian dogmas seem to be in need of an overhaul.
Gerontologist and philosopher
I believe so many things without proof that I am spoilt for choice. As Karl Popper pointed out, no belief can be legitimately placed beyond the reach of doubt. There is always the possibility of further observations that may prove it wrong. Take, for instance, the statement: “All swans are white.” It looked pretty unassailable until visitors to Australia reported sightings of black swans. And if I extend the notion of reasonable doubt virtually everything within the borders of our known world can be doubted.
Here are two of my most stubborn beliefs: first, that the material objects which populate my world are not just the sum total of my experience of them. Some philosophers argue that you can reduce objects to the personal interaction you have with them; outside of that, they don’t exist. I believe the opposite. I believe — despite proof that still confounds the brightest philosophical minds — that material objects exist outside of my own relationship with them. Second, I believe that our all-too-human religions, which are organised around an all-too-human idea of God, have nothing significant to say about how things really are, compared with our everyday perceptions.
SIR JOHN KREBS
Principal of Jesus College, Oxford
I believe that Mozart was a better composer than Carl Stamitz, a lesser-known contemporary. I do not know how I would prove this, or any other kind of aesthetic superiority. If public reaction to a musician was enough, that would solve it but, if an independent objective proof is required, it’s close to impossible. There is a chance that one day we will arrive at a formula that will explain why music X is better than music Y. We may discover that certain music elicits a larger release of serotonin in listeners. Alternatively, that a brilliant painting sends certain messages from the retina to the brain.But I doubt it very much. Nor do I think it would be a good thing. By reducing art to science, you risk losing the essence of what you are trying to explain. In other words, the X-factor that makes it superior. Art involves individual judgment and, therefore, it’s not quantifiable. The only good thing would be that I’d be able to find other composers I’d like by applying the magic formula.
Sir John Krebs is the speaker at the Royal Institution’s Christmas Lectures, from December 26-30. To book, visit www.rigb.org 
Professor of complementary medicine
I don’t believe in anything that I can’t prove. My only true belief is in science and its ability to sort out belief from fact. Part of my fascination with alternative therapies stems from the fact that some of them have not yet been proved. My job is to establish whether or not they are evidence-based. There is no aspect of belief in this at all. If there is, it gets in the way and becomes a bias. Once you have tested and established your hypothesis, you try to disprove it. If you can’t, you do the test again before you consider believing it. If you find the results contradict your belief, you abandon it — or you’re a fool. This is why I am convinced of the power of placebo. I have done trials with patients who suffer from intractable pain. A portion of them, who were seen by actors pretending to be spiritual healers, improved so significantly that some were able to abandon their wheelchairs. This is this kind of proof I look for before I believe in something.
What We Believe But Cannot Prove, edited by John Brockman, published by Free Press (£9.99), is available from Times Books First at £9.49 p&p is free. Call 0870 1608080 or visitwww.timesonline.co.uk/booksfirstbuy