Science kills an awful lot of animals. According to the latest Home Office statistics on the use of animals in scientific research, over 2.6 million rodents, rabbits, cats, dogs, ferrets, pigs, sheep, primates, and birds were used in scientific procedures in the UK in 2002. That's roughly four animals destroyed for every human child that is born. And this is a conservative assessment, since the two million rodents killed in 2002 constitute as little as 20 per cent of the total number of mice and rats which are bred for research and then destroyed, the surplus being excluded from the count because they are not 'used' in experiments.

Of course, all experiments on animals are regulated. Scientists are required to minimise harm, to demonstrate the benefits of their research, and to ensure that there are not alternative methods, which don't use animals, before commencing. The concern for animal welfare which underpins these regulations might well be seen as arising from a mature doctrine of humanism, which recognises that our species does not have a monopoly on the capacity to suffer, and that pain is an evil no matter which animal experiences it.

But any comfort that we might feel with the present state of affairs, any confidence that we possess in the current regulation of animal research, may be short-lived. This is because the nature, as well as the number, of animal experiments is rapidly changing. Over a quarter of the scientific procedures carried out on living animals in 2002 involved some form of genetic modification. Experiments on genetically modified animals now constitute the fastest growing category of research.

The genetic modification of animals forces us to face a quite different set of ethical issues than those raised by the established practices of vivisection. Consider the news that some animal rights thinkers have begun to suggest that genetic manipulation could be used as a means to protect, if not enhance, the welfare of animals. The American philosopher Bernard Rollin, for example, argues that wherever animals are bred and maintained in conditions which are not congenial to their wellbeing, the possibility arises of changing the nature of those animals to better suit the environment in which they are confined.

To combat the cramped and unsanitary conditions of the battery farm, for instance, pigs and poultry could be genetically engineered with improved disease resistance, and greater tolerance of extreme temperatures, drafts or excessive humidity. Chickens could be produced which lack the desire to nest, high-volume dairy cows could be made immune to mastitis, and cattle could be genetically manipulated to enable them to digest protein-rich cereals and hay without suffering from bloat, diarrhoea and acidosis. Israeli scientists, using low-tech cross-breeding, have already produced a featherless broiler chicken which can survive the often lethal temperatures of the Middle East. Back in the laboratory, animals could be created which lack cerebral functioning, thus allowing scientists to experiment on them, or grow them for food, without moral restraint. As Rollin writes of the livestock industry: "If we could genetically engineer essentially decerebrate food animals, animals that have merely a vegetative life but no experiences, I believe it would be better to do this than to put conscious beings into environments in which they are miserable."

Rollin's reasoning hinges on the argument that a concern for animal welfare is a 'moral' concern, whereas feelings of disgust, revulsion or disquiet over what is effectively the creation of new creatures, are merely 'aesthetic', and thus a question of personal taste.

Consider the possibility that some time in the future scientists will be able to use cloning technology to grow choice cuts of meat without creating and raising animals themselves. What reason – other than 'aesthetic' – would vegetarians have to remain vegetarian, when they can eat meat without having to worry about animal welfare?

Consider another scenario. As technology progresses, scientists will also be able to grow human body parts without creating viable human life. Would you, as a meat eater, then eat the flesh of your own kind (I'm told it tastes rather like pork), comfortable in the knowledge that no human had been harmed in its production? I suspect you wouldn't, and society would be outraged at the proposal. If we are prepared to grant this outrage some ethical status (though dissenters may deny this on the grounds that revulsion is a primitive, or 'aesthetic', sentiment impervious to moral reasoning), then it does appear that the argument that our moral responsibility for other beings ends once we have protected them from suffering breaks down.

It seems that adopting a moral ('humane') relationship to other creatures involves more than a dispassionate recognition of their capacity to feel pain, and more than a utilitarian calculation of the benefits which inflicting such pain may deliver to us. Our overriding disgust at the prospect of farming human flesh – and, for that matter, of pigless pork, featherless chickens, brainless rats, and animals engineered to suffer diseases that do not naturally afflict their kind – implies something more. It implies a desire to protect and respect what those creatures naturally are. It implies an acknowledgement of the independence and integrity of other beings. It suggests that we value living things not simply by virtue of their usefulness to us, but because they precede and are independent of our own existence. It is in this same spirit – which has a natural kinship with the spirit of human love – that we feel we can come to truly know other creatures only when we accept their fundamental mysteriousness to us.

This moral sensibility is compromised when we manipulate the genetic foundation of other animals, as if we could build them up from scratch in accordance with our most meticulous plans and fantasies. It is also compromised by the manufacturing of disposable body parts, since this blurs the boundaries of the things whose integrity matters so much to us, and makes us think of these beings – ourselves included – as assemblages of the very parts we can now manufacture. The prospect of eating manufactured human flesh disturbs us because it dilutes our sense of reverence for the human animal. It perforates the boundary between what we are, and what we make ourselves to be, and in doing so makes us feel disposable.

What is equally evident is that moral consciousness is as much a product of feeling as it is the outcome of lucid reasoning. Without a sense of emotional conviction, our moral choices would lead to promiscuous and ultimately conformist forms of action. True, we may be able to reason with rigour and logic. But without personal convictions, the parameters of our deductions, the 'facts' to be included and those to be ignored, the relative weighting of the relevant variables, will all be determined on our behalf by the dominant interests and the prevailing logic of our society.

Once we recognise the importance of feelings to moral conduct, then suddenly the rationalist argument for the instrumental manipulation of animals begins to look more problematic. A concern for those animals – for their integrity as well as their welfare – is not a question of 'mere' sentiment. Sentiment is the stuff of moral convictions, and we sustain those convictions by extending our sentiments and enriching them through ritual, symbol, and culture. Our revulsion towards eating manufactured human flesh is not so very different from the choice of many vegetarians to eschew imitation vegetarian 'meat'. Like their disgust at the sight or smell of meat, and their need to avoid contamination by meat products, this is not an expression of dogmatic fundamentalism, but rather an attempt to enliven their moral commitments with physical sensitivity and feeling.

In his manuscripts of 1844, Marx famously described the human animal as a 'species-being', by which he meant that humans harbour the unique capacity to fashion relations of productive co-operation which stretch beyond narrow kinship ties to include potentially every member of our species. A mature humanism must take this insight further, for we should also be proud of another distinctive trait: the ability to restrain our promethean desires in order to include other species – not as fellow workers, but as fellow forms of life – in a more generous circle of care.

Finn Bowring is the author of Science, Seeds and Cyborgs: Biotechnology and the Appropriation of Life