The short but acute media furore that attended the publication of Stephen Hawking's latest co-authored book, The Grand Design: New Answers to the Ultimate Questions of Life, was inevitable. Perhaps because of that unique combination of the profundity of his disability and the apogee to which his thought ascends, Hawking has developed an enviable status as a modern oracle. And when Hawking finally pronounces the non-existence of God - a subject upon which he had maintained a studied (if doubtful) agnosticism until now - the world sits up and listens.

Compared in style alone to the tub-thumping atheist evangelism of some of Hawking's contemporaries, The Grand Design, couched in the language of cosmology and conceptual abstraction, has more of the air of a papal encyclical.

In most respects (and disappointingly), the message remains the same nonetheless. Whether we are talking about the evolutionary moment between monkey and man, the emergence of the complex mammalian eye out of simple photosensitive receptors in amphibians, or a grand unified theory for what happened between the first and second 50,000th of a second after the formation of the Universe, the physical processes of causation, determined by the impersonal laws of nature, are sufficient to explain the existence of the world around us.

Moreover, given that large hands do not appear occasionally out of clouds to adjust the planets, divine intervention is neither theoretically necessary nor empirically demonstrated. There are simply no gaps for God to reside in.

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For Hawking, theology and creation myths of all kinds are simply the product of an intellectual innocence turned bad.

"Ignorance of nature's ways led people in ancient times to invent gods to lord it over every aspect of human life...since the connection of cause and effect in nature was invisible to their eyes, these gods seemed inscrutable, and people at their mercy."

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As time progressed, humans became more knowledgeable about the world, dispensing with the need for anything other than science to answer the big questions of Life, the Universe and Everything. Theologians and philosophers have had their day, and "scientists have become the bearers of the torch of discovery in our quest for knowledge".

So far, so predictable. What is striking and honest about the arguments in this book, however, is how many of them are applied even-handedly to both gods and men. If the divine creator is unfindable through the methods of science, we will have an equally hard time finding the individual human person, at least in the way we ordinarily think about them. While I believe that my colleague in the office next door is a person - that he has intentions, thoughts and emotions, that he is the author of his actions - these are not empirically available to me, nor does science support such a description.

I can in theory fully explain the elevation of my daughter's arm in terms of the tensile strength of bones, the leverage of muscles, the transfer of nutrients, the sparking of electrical signals across neurons. For Hawking, this means that I cannot and indeed should not attribute that lifting to her own will. Like the twitching frog legs on Galvani's bench, human behaviour is no more than chemicals, electricity and levers; intimations of intention - of free will - are merely an "effective theory", a necessary approximation for understanding a "biological machine" too complex to calculate.

This is of course an age-old dilemma: Alan Turing struggled to define exactly what it is that proves that a certain set of behaviour is produced by a person and not a very sophisticated machine. Longer ago still, the Catholic Church debated for years whether the Amerindian natives who were caught up in the Spanish slave trade were actually human and had souls, or whether they could be treated like any other animal or automaton. Only with the papal bull of 1537 were they declared fully human (ironically, because they believed in a supreme deity).

Hawking's answer, perhaps unsurprisingly, is not that of the Vatican: for him, both God and the free human individual are primitive fantasies.

What The Grand Design drives home is how difficult it is to defend the study of people (as opposed to humans as biological machines) from an objective scientific standpoint. The individuality that makes me different from you, or that describes the actions, thoughts and policies of King Henry VIII, does not show up well on scientific instruments. Like God, people as individual agents - as authors of their own fates, as creative beings - are scientific chimeras.

In many ways, this explains an important feature of the academic debate between science and religion. While the views of natural scientists, philosophers and theologians are constantly splashed across radio, TV and printed pages, the silence from the social sciences - from anthropologists, sociologists, political scientists and historians - is deafening by comparison.

This is doubly strange because, while writers such as Richard Dawkins have often been accused of a woeful lack of actual knowledge about religious life, many social scientists (such as myself) are professionally obliged to study it. Anthropologists and sociologists in particular spend years among religious communities, examining rituals and sacred texts, tracing the dynamics of sectarian hatred, theocratic rule and the blood and loss of religious wars. And yet one would have to work hard to find anything like Dawkins' The God Delusion or Victor Stenger's God: The Failed Hypothesis written by a modern cultural anthropologist or sociologist.

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So, why the reticence? Surely social scientists have something to say? Well, in private many do. Most social scientists are not personally religious, are in general agreement with the fundamental premises of Darwin's On the Origin of Species, and find arguments about the Big Bang wholly convincing. When pressed at parties, they will often admit that many of the beliefs and myths of those they study are probably rubbish.

However, their professional view as social scientists is often radically different. After all, unlike the natural sciences, which generally regard religions as intellectual competitors, the social sciences study religion much like a biologist studies amoebas or an astrophysicist studies supernovae.

This distinction changes everything. A physicist would not ask whether one supernova was more or less accurate than another, nor would a biologist seek to separate out the "true" amoeba under his microscope from the "false" ones: the question is nonsensical. In a similar way, the anthropologist studying the rituals of some distant Himalayan village precludes the question of their truth or falsity, precisely in order to achieve scientific objectivity, not in opposition to it.

This has been a basic methodological principle of the study of religion since ?mile Durkheim penned The Elementary Forms of Religious Life in 1912.

At the same time, however, social scientists need to deal with a facet of data that their natural science colleagues do not: their research subjects talk back. Volcanoes, amoebas, virus pathogens and chemical compounds occasionally may be noisy, but they don't speak. In particular, they don't contradict your conclusions when reading your research drafts.

When people say things, such statements have meaning, meanings that cannot be ignored any more than any other kind of evidence. In order to listen to a conversation, I must assume that the two people speaking to one another are conveying meaning. If I want to understand a simple purchase in a shop, I need to employ the ideas of money and value that those doing the shopping are employing, or the transaction I observe won't make any sense.

The importance of capturing that meaningful, subjective dimension of human behaviour stood at the heart of Max Weber's seminal works in the early 20th century. They defined the discipline of sociology not as the study of objective physical behaviour, but of meaningful human action, interpreting which required empathic understanding (verstehen) as a necessary prelude to proper theory-building about people. When a social scientist employs verstehen, he is engaging with those he is studying as another person, not as a scientific instrument.

The problem, however, is obvious. Understanding political, religious, kinship and economic life all depends on inferring the existence of meanings and intentions that we can neither see, hear, smell, taste or feel. For example, "being married" is in no sense empirically testable: it does not change our genetic code, the valence of our atoms or our colour - there is no Geiger counter for the married state. Rather, to know that a person is married, you have to ask someone (the individual concerned, the priest, the state official) or consult a document (the marriage register) and trust that answer. Even the wearing of rings or tattooing or scarification of the body that attends some wedding ceremonies around the world only "make" someone married if you engage with what the people of a particular society tell you.

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The overwhelming majority of phenomena that social scientists study are much the same: religious practices, political affiliations, nationalities, state institutions, financial or legal standing - all are meaningful, indeed findable, only once one engages with the subjective meanings of those enacting them. None of them has any objective status as the natural scientists would understand that term.

Indeed, it would not be an overstatement to say that proving the existence of, or talking systematically about, most social science concepts seems to be as elusive as proving the existence of the divine. God, it would seem, is not alone in our doubt.

These basic methodological problems are, of course, fully known to most social scientists and quite a few natural ones, and the issue does not go without comment. While the place of God and religion may take centre stage in the battle of what counts as appropriate knowledge in academia, an equally ferocious - if less openly declared - cold war endures between the natural and social sciences, particularly when it comes to the place of evolutionary theory in understanding the activities of human beings.

In a recent special edition of The Journal of Evolutionary Psychology, the social sciences were accused of rejecting evolutionary theory when it comes to explaining human behaviour, and of indoctrinating students with "anti-Darwinian" views. Socio-cultural anthropology in particular was described as fatally infected with a cultural determinism that privileges social factors to the almost complete exclusion of biological ones.

In an article by the biological anthropologists George Perry and Ruth Mace, socio-cultural anthropology is likened to religious studies (and indeed religious groups in general) in its idealist rejection of biological realities.

Unsurprisingly, perhaps, this is an area upon which Richard Dawkins has strong views. He accuses social theorists of a hand-wringing malaise of political correctness that makes them incapable of taking a principled scientific stance, calling a spade a spade and simply stating that religious believers are, well, wrong.

As he writes in River Out of Eden: A Darwinian View of Life: "Show me a cultural relativist at 30,000 feet and I'll show you a hypocrite...If you are flying to an international congress of anthropologists or literary critics, the reason you will probably get there - the reason you don't plummet into a ploughed field - is that a lot of Western scientifically trained engineers have got their sums right."

And in A Devil's Chaplain: Reflections on Hope, Lies, Science, and Love: "If I am in the witness box and prosecuting counsel wags his stern finger and demands, 'Is it or is it not true that you were in Chicago on the night of the murder?'...I would not expect a jury, even a Bongolese jury, to give a sympathetic hearing to my plea that, 'It is only in your Western scientific sense of the word "in" that I was in Chicago. The Bongolese have a completely different concept of 'in', according to which you are only truly 'in' a place if you are an anointed elder entitled to take snuff from the dried scrotum of a goat.'"

At a deeper and more philosophical level, materialist philosophers such as Patricia and Paul Churchland reject in principle the very existence of intentional states such as believing, feeling and knowing as elements of a "folk psychology" that are at best a working shorthand, at worst a serious theoretical error, with no place in the scientific study of human behaviour.

This view of human behaviour may well be objective and scientific, but it represents an account of humanity that is for most ordinary readers alien, counter-intuitive and difficult to think with, precisely because it rejects the everyday "folk psychologies" that humans use to understand one another. Indeed, the sheer number of human activities and institutions that can be studied only though an interpretative approach means that objective studies of human behaviour remain locked at a remarkably low level.

Paleoarchaeology and evolutionary psychology by and large restrict themselves to understanding processes of staggering generality (the reproduction of inherited behaviours, the possibility of human altruism, the acquisition of language) or the development and evolution of human artefacts. Either way, the vast panoply of human activity as most of us would understand it remains presently (and perhaps permanently) beyond its reach.

When it comes to understanding something as basic as the activities of human beings, then, the academy is divided. The social sciences sometimes hardly seem scientific at all, while the natural sciences cannot provide an account of human behaviour that is either rich enough to account for its diversity, or human enough to be accessible or meaningful to the rest of us.

For some, this divide is an endemic feature of academic life - part of C.P. Snow's "two cultures", which cannot, and perhaps should not, be overcome. After all, the odd disagreement is good for the soul of the academy. For the more radically inclined, such diversity and disagreement is anathema: the grand progress of scientific knowledge should be exactly that, and the social sciences from anthropology to history and linguistics should either reform or be taken over.

More moderate voices, however, speak of the possibility of cooperation. Lamenting the failure of the social sciences to adapt evolutionary theory, Robin Dunbar of the University of Oxford's Institute of Cognitive and Evolutionary Anthropology puts this down to its misplaced association in the minds of social scientists with now-discredited racist and eugenic programmes, a hangover from the early 20th century: "My concern is that if we do not rebuild these bridges, evolutionary biology and the social sciences will engage with the same questions and material, but wend their separate ways and so fail to benefit from the insights that each can offer."

Indeed, many evolutionary specialists regard the vast "datasets" of the social sciences as a potential gold mine of information on human behaviour ready to be tested by the new Darwinian theories. But can such a goal be achieved when there is such disagreement over the very principles by which those data were gleaned? Would evolutionary theories of human activity be testing human behaviour or human action?

Ultimately, such problems may require more than a quick primer in evolutionary theory for wayward anthropologists. If our understanding of humanity is to progress, then academics in both the natural and social sciences need to come to some kind of resolution over what they mean by legitimate and useful knowledge within the academy. Thus far, that "resolution" has largely involved the lobbing of brickbats between departments.

What seems to be missing is a common sense of a mutual intellectual problem that actually needs to be solved. Resolving the relationship between objectively available behaviour (which we can all point to) and subjective intentional experience (which we all know exists), and constructing a suitable framework for unifying those within a rigorous scientific methodology are genuinely difficult puzzles worthy of a central place within our attention.

The standard answers to this problem will no longer do. The mind-body dualism of Ren¨¦ Descartes and Franz Brentano arguably got us into this mess in the first place; the materialist declaration that private mental states do not exist and can effectively be ignored persuades almost no one; the monist assertion that the mental and the physical "are one and the same" sounds good but seems to explain nothing. We desperately need a theoretical rather than a philosophical answer to this conundrum, and one that has some degree of predictive value. After all, had Michael Faraday and James Clerk Maxwell taken a purely philosophical approach when trying to unravel the relationship between electricity and magnetism, and not bothered with all that awkward business of developing an intermediate field theory, we might be puzzling over it still.

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At the end of the day, if we are not to tear ourselves apart or drive ourselves mad, we need a better, deeper understanding of what it is to be human - and that would be the grandest unified theory of all.