The theory of evolution, which postulated a common biological origin for humans and animals, was once liberating. It challenged the belief – from which so much evil had sprung – that, alone among living creatures, we had been created in the image of a Supreme Being. Darwin's thesis that all species were the products of natural selection was overwhelmingly persuasive; so too was the conclusion that the process no more required the specific interventions of a Creator than did the formation of rocks. Advances since Darwin have shifted the emphasis from the survival of the organism to that of the genetic material expressed in it. The organism is simply the neccessary means by which genes seek to ensure their own continuation through replication.

This shift of emphasis, however, does not alter the fundamental significance of Darwin's brilliant conjecture, whose truth one would have to be a madman or a creationist to deny. 'Gene-eyed' evolution is as godless, and as unconscious, a process as the original version which, as Samuel Butler famously put it, "banished mind from the universe."

And this, via a serious misunderstanding, is why one hundred and fifty years after The Origin of Species, the theory of evolution is no longer a liberating force. It is now invoked to minimise the differences between humans and animals, and to deny the role of mind, of self-conscious agency, in human affairs. In the hands of some of his modern interpreters, Darwin's great idea has become a serious obstacle to thinking straight about mankind.

Having helped us to escape the prison of a supernatural understanding of ourselves, Darwinism is now being used to imprison us in a no less dispiriting naturalistic understanding. Contemporary evolutionary thought not only denies theological explanations of the exceptional nature of human beings but also that exceptional nature itself. John Gray's Straw Dogs is only the latest of numerous books arguing that anyone who believes that we are more than just animals is still in the grip of the same tired theological delusions that Darwinism was though to have successfully discredited.

Darwinism, in short, has been transformed into 'Darwinosis'. This pathological variant holds that the theory of evolution has shown that not only are we descended from animals: we are no different from them; or at least not in those respects that matter most to us. That we are beasts, and hence are just as unfree as they. That we continue to think of ourselves as free, this is only because it is of adaptive value to be thus deluded, and to imagine that we are rational agents. That, in practice, the reasons we ascribe to our actions are not their actual causes: And that our sense of agency is merely our muddled awareness of the impersonal forces – cultural or biological – that are acting through us.

Darwinosis is the most radical denial of the place of conscious agency as opposed to unconscious forces – in this case the survival tactics of genes – in shaping human lives. If it were a true account of things, it would have dire implications for human freedom and for the idea that we know what we are doing and why.

Even so, it is very difficult to contest, without seeming to be a closet creationist, or a deluded sentimentalist running away from the implications of what the philosopher Daniel Dennett dubbed "Darwin's dangerous idea."

It is no use pointing out the obvious differences between human beings and all other animals. It is equally futile drawing attention to the obvious fact that human actions are shaped by complex, abstract frames of reference, in part constructed out of factual knowledge, that have no counterpart in the experiences and behavioural drivers of all other animals. For the biologisers of humanity are extremely effective at eliding the huge gap between humans and animals by anthropomorphising or 'Disneyfying' what animals do and 'animalomorphising' what human beings get up to.

The Disneyfiers of animal behaviour seem unable to recognise any limits. In his recent (and largely excellent) Nature via Nurture: Genes, Experience and What Makes us Human Matt Ridley speaks of the microscopic worm, Caenorhabditis elegans, as showing 'flexible learning'. He discusses the difference between 'social' worms that "go to school" (ie are housed in a Petri dish with other worms) and those that are "kept at home", and how they develop different adult 'personalities'. C. elegans has no brain and a princely total of 321 neurones!

Criticising the language of the biologisers is not, however, enough. Defenders of human exceptionalism must, given our undoubted biological origins, find a 'biological' basis for our unique escape from biology and a 'biological' explanation of how we acquired the ability to run our lives – as opposed to being run by genes that happen to delude us into believing that we are running our lives. Given the relative triviality of the genotypical and phenotypical differences between ourselves and our closest primate cousins, this may seem a tall order.

It is, however, possible to find a clue to the radical and widening difference between ourselves and all other creatures, as was first suggested by the pre-Socratic philosopher Anaxagoras: the hand.

Why should it be the hand that makes us so radically different, even from our nearest primate kin? And how does this difference allow us to be free as no other living creature is?

The most remarked upon feature of the human hand is something that at first sight seems rather minor: full opposibility between the finger and the thumb. Other primates have quite versatile hands, with independent movement of the fingers, but at best have only partial opposibility of the thumb and other fingers. The spectacular gain in dexterity resulting from full opposibility is self-evident but this would permit us only to be rather gifted chimps and as much prisoners of our biological inheritance as they. To understand the immeasurable impact of possessing a full-blown hand, it is necessary to appreciate the (almost incidental) transformation it brought about in the hominid's relationship to its own body. The key to this is a combination of 'meta-fingering' (the digits fingering each other in manipulative activity) and 'constrained manipulative indeterminacy' (a range of available grips to choose from to achieve any particular task). The hand is self-addressed as no other organ in the animal kingdom, and it has a prodigal inventiveness permitting choice also unmatched in other living creatures. This not only allows peerless versatility but makes the hand the bearer of a higher level of bodily self-awareness. In particular it makes the hand a 'proto-tool' – something the hominid organism consciously uses. The tool-like status of the hand in turn instrumentalises the human organism as a whole and ignites the sense of agency, and indeed, subjectivity within it.

Centrally, the hand awakens an 'existential intuition' – the first person sense that 'I am this (body)'. This intuition lies at the root of the selfhood an the agency that sets humans apart from all the other animals. The hand started the process whereby, over many generations, the human person began to wake up in the hominid organism; to wake up out of embodiment to embodiment – and to the sense of there being something (more precisely someone) that is embodied. The hand's role was reinforced by several other, roughly contemporary, developments. The most important was the assumption of the upright position which, as Charles Sherrington pointed out, freed the hand from the job of being a simple locomotor prop to being "a delicate explorer of space". It may seem implausible to claim that something as contingent and as slight as a difference in the functional anatomy of the hand should have such momentous consequences. We may, however, assume that other primates were close to the threshold that humans crossed; there is, for example, evidence of fleeting self-consciousness, nascent selfhood, in chimpanzees. In other words, the hand didn't have to deliver much in order to start the process by which humans became ever more self-aware and distant from their status as organisms and ever more clearly defined as 'subjects within their own bodies'. The hand did not build self-consciousness from scratch but made it more continuous.

Once the threshold was crossed, a feed-forward mechanism, with increasing elaboration of self-consciousness and agency, began. This was soon driven mainly by secondary consequences of the possession of a proto-tool. The most important secondary consequence was the spread of instrumentality beyond the hand and the body. The tool-like hand inspired the use of tools outside of the body. Although non-human animals also seem to use tools, their low-ceilinged, stereotyped forays into apparent tool-use are not rooted in an instrumentalised awareness of their own bodies: their fleeting tools tend to be assimilated into undifferentiated body schemata, rather than being polarised within it. Despite appearances, therefore, animal tool use is not analogous to human tool-use. Human tools not only extend the scope of agency: they also intensify the sense of being an agent and with this, expand the aura of possibility that, for an emergent agent, surrounds actuality. Artefacts, explicit extra-corporeal tools, have important incidental properties: they place an image of agency, and of generalised human intentions, even of needs and the path to their satisfaction, outside of the body. They make these things public. This promotes the collectivisation of the consciousness of members of the human species, paving the way from the essentially solitary sentience to which other animals are confined towards the socialised (and eventually factual) knowledge, that only humans enjoy. Essentially solitary animal needs are pooled into the explicit scarcities that human collectives attempt to address.

The central role of hand-inspired tools – artefacts which externalise agency, needs and intentions – in promoting distinctively human forms of socialisation, has been attested to by many palaeo-anthropologists. Tools are also, incidentally, abstract and in some sense arbitrary signs and their use involves skills, and mobilises areas of the brain, overlapping with those ultimately involved in speech.

They are therefore highly plausible precursors of (unique) human language. Furthermore, all of these developments – instrumentalisation of the hominid body, the use of tools, collectivisation of consciousness, and finally the emergence of language – both drive and are driven by increased connectivity of the human brain.

The collective awakening of humanity out of organic being is progressive, being initially rather slow (over a million years separates the pebble chopper from the hand-axe!) and then accelerating to its present dizzying rate.

There are many obvious objections to this reconstruction of how, as the German philosopher Schelling said, "in man nature opened its eyes and noticed that it exists".

The difficulty of believing that something as localised as the hand could have such global effects is rather like the difficulty of believing that that small orange object in the sky made all life possible: it is dwarfed by its endless consequences, cooked up over a long time.

Even if it were accepted that the hand made us uniquely self-conscious, what relevance would this have to the truth of our belief in our freedom, our unique status as agents?

Given that we are organisms and organisms are part of nature, the notion of human beings as genuine doers, rather than merely sites of events, seems difficult to sustain. Even so, I firmly believe that the consequences of handedness can provide a credible basis for our emergent freedom.

A genuinely free act is one whose origin lies within ourselves and is not foreordained by the laws of nature: the actor could have 'done otherwise' had he so willed. In order to see how we can be free – collectively and individually – we have to think about the existential intuition awoken by the hand: "That I am this...". The assumption of the human body by itself, as 'my' body, as what I 'am', is the seed of selfhood.

The growing self expands that point of origin to an increasingly robust springboard from which actions may arise. While that which 'is' is a product, that which 'I am' is no longer a product. This still does not take us all the way there. I may assume my body as myself but I could still be a mindless, insightless collection of gene products. We have not yet demonstrated that humans are able to deflect the course of events or, collectively create a place outside of nature that cannot be understood in biological terms.

Breaking the laws of nature in the name of freedom is not an option. Fortunately, true agency and freedom do not require this. As John Stuart Mill pointed out (in a posthumously published essay Nature):

"Though we cannot emancipate ourselves from the laws of nature as a whole, we can escape from any particular law of nature if we are able to withdraw ourselves from the circumstances in which it acts."

This enables human beings to conceive of agency as the ability to choose between laws of nature (or, in the case of pre-scientific humankind, between patterns of happening).

By this means, we may be able to re-direct nature to ends that were not prefigured in the general laws, or ends at least that nature did not have in view. This process is clearly distinct from the idea of human agency as a special, esoteric or supernatural kind of cause. It does, however, require an 'outside' from which the choosing could take place.

The outside from which we choose between laws of nature is the realm of first-person being, of the self, of 'I am', which becomes ever more complex and elaborated as successive generations of increasingly self-conscious, increasingly effective, human agents pool their resources to create a distinctively human realm. The basis and the proof of the reality of human freedom is this extra-natural world which is now 'wall-to-wall'.

The human journey towards our present distance from nature began several million years ago. Gradual and collective, it has in part been based upon an illusion: at each stage, our reach has exceeded our collective grasp in a space of possibility opened up by tools which transform awareness of the needs they serve, changing appetite from something suffered and instinctively reacted to, into something understood and acted upon. To deny our unique margin of freedom and the role of consciousness, agency and reason in our behaviour is to deny that journey.

This denial is not obligatory for those who accept what evolutionary science has to say about our biological roots. One can be a good Darwinian without reducing our cultural leaves to their biological roots: confusing the former with the latter is not biology but biologism, not Darwinism but Darwinosis. Attacks on the notion of humans as self-conscious agents who have some idea of what they are doing, are important for the obvious reason that they undermine hopes for the future.

If we believe we are imprisoned in our biological past, we cannot believe in bringing about a better future because our past is shaping the future in our stead. This is not so; our hands, waved goodbye to the animal kingdom and several million years ago.