There is an episode of Star Trek in which Data, the android who would be human, disobeys orders and puts at risk the life of his captain Jean Luc Picard to prevent the destruction of machines he believes to be sentient. Far from being outraged, Picard congratulates Data. It was, he tells him, 'the most human decision you ever made'. In the Star Trek universe, humans are not simply physical beings but moral entities: creatures of choice, beings who are forced both to define right and wrong and to act upon it. That's why Data's most heartfelt aim is to become human.
'Don't bother', Felipe Fernández Armesto would undoubtedly have counseled him. Humans, he suggests, are not especially moral and certainly not superior in any fashion. Indeed it is difficult to define what a human being is. So you think you're human? Well, it's time you left your Star Trek fantasies behind and returned to the real world. It's not that Fernández Armesto denies that humans exist. It's rather that he sees humanity as an 'elastic' concept that should include, among things, chimps, Neanderthals, the unborn - and probably androids too. So You Think You Are Human? is a history of 'humankind', not of the beings that call themselves human, but of the idea that such a being exists. It is also a polemic against that very idea - at least in the way we conceive of it. 'Those of us who think we are human feel utter confidence in our human identity and our ability to recognise it in others', Fernández Armesto writes. 'Yet our present concept is a recent contrivance: most people in most societies for most of history would have been astonished by such an all-encompassing category. Most of them, indeed, would have had difficulty in understanding the word "human" or find an equivalent for it in their own languages, except as a way of designating members of their own group.'
Fernández Armesto shows how historically humans have tried to establish the boundaries of humanity by excluding other animals, other human groups - viewing different races as 'subhuman' - and other hominid species, such as Neanderthals. Policing the frontiers of humanity in this fashion, he argues, is both practically futile and morally suspect.
The idea that humans should be viewed as distinct from animals is a recent cultural conceit. The idea cannot be traced back before the first millennium BC - 'the "axial age" when so much of our modern thinking was initiated or anticipated by sages in China, India, the near East and Greece.' On the other hand, 'Our remote ancestors seem to have accepted without question that they were part of the great animal continuum. For the earliest creatures we might reasonably classify as human, this was actually an observable fact, since for most of the hominid past they coexisted with other, similar species.' How Fernández Armesto knows what our remote ancestors thought about 'the great animal continuum', I'm not sure.
That belief in human exceptionalism has coincided with the development of civilisation and the rise of a more rational view of the world might suggest that there is some merit to the idea. But no. Modern science, Fernández Armesto argues, sides with our remote ancestors against the sages of China, India, the near East and Greece. Over the centuries many thinkers have pointed to some specific quality - culture, reason, tool-use, language, morality - as that which makes humans distinct. Fernández Armesto collects the scientific evidence to show none of these qualities is uniquely human. Chimps can make and use tools. They have been taught sign language. Many animals can reason about the world. In fact they seem to live very much as we do. Female bonobos have been seen to put dead rats on their heads; this apparently is a form of 'haute couture'. Chimps at the Yerkes Primate Centre in America 'gather together to sway and stamp in a concerted fashion' at the approach of heavy rain. This 'looks like magical behaviour - evidence of a sense of transcendence or the power of prayer.'
Fernández Armesto is clearly more impressed by Jungle Book than by Star Trek. Real science, inevitably, is a lot less cartoonish. Animal behaviourists often think of an animal as if it were a rational agent capable of making choices and driven by human-like motives. Why? Because it a useful way of analysing behaviour. But, as the ethologist Patrick Bateson points out, 'Attributing the power of making choices to an animal, so that we can do more imaginative science, does not mean, when our efforts are crowned with success, we have proved that the animal has chosen.' In other words, even when animals behave in a human-like fashion, they do not necessarily do so for human-like reasons. Humans may be animals, but animals are not human. It is human sentimentality that transforms nature into Disneyland.
Science tells us that in some ways humans are similar to other animals and in some ways we are different. But what meaning should we impute to these similarities and differences? That is a political and philosophical issue, not a scientific one.
Take, for instance, the question of culture. Fernández Armesto defines culture as 'any widespread behaviour that is transmitted by learning rather than acquired by inheritance'. By such a definition many non-human animal are 'cultured'. Primatologists so far have discovered some 39 habits that distinguish one groups of chimps from another. One group is able to hunt for termites with a stick, another to use two stones as 'hammer' and 'anvil' to crack open palm nuts.
Humans, though, do not simply acquire habits from others. We also constantly innovate, transforming ourselves, individually and collectively, in the process. There is a fundamental difference between a process by which certain chimpanzees have learnt to crack open palm-nuts, and a process through which humans have created the industrial revolution, unravelled the secrets of their own genome, developed the concept of universal rights - and come to debate what it is to be human. All animals have an evolutionary past. Only humans make history.
This is not an argument that impresses Fernández Armesto. 'Most human societies for most of history', he argues, have developed barely at a faster rate than the great apes. Indeed, the most successful humans are the ones that are most chimp-like. It is 'glib' to hail the 'great civilisations' which have 'achieved spectacular progress, expansion and environmental transformation' as 'models to copy'. Rather, 'the most successful societies are the ones that have changed the least, that have preserved their traditions and identities intact' and have 'successfully resisted the risks of change'.
It is ironic that as distinguished a historian as Fernández Armesto should so easily dismiss the history-making capacity of human beings as irrelevant to our humanity. If you view the most chimp-like of human behaviours as characteristic of the species, then, of course, it makes sense to deny the distinctiveness of humanity. But such denial is rooted not in science but in a philosophical pessimism about the meaning of humanness.
In the final chapter Fernández Armesto looks not to the past but to the future – to the consequences of the genetic revolution for our concepts of humanity. He is fearful, agreeing with Francis Fukuyama that 'biotechnology will cause us in some sense to lose our humanity'. But if 'we do not know what makes us human', how can we lose it? And if humanness is so 'elastic' a concept to encompass both Neanderthals and chimps, why can't it also encompass genetically engineered human beings?
Fernández Armesto's inclusive concept of humanity appears progressive; in fact it has quite reactionary consequences. This becomes clearest in his argument about the unborn. 'The unborn', he tells us, 'are the great underprivileged minority of our day, whom we can exterminate without a qualm.' A definition of humanity that 'excludes the unborn' is akin to a definition which excludes Jews or blacks. Abortion is a 'massacre of innocents'. Therapeutic cloning - the use of embryonic stem cells for medical purposes - is ethically 'repellent'. Fernández Armesto has opened the gates of humanity to the foetus - but only by closing the door to the rights of women and the needs of those suffering from a myriad of illnesses.
Fernández Armesto is right that there can be no single or simple definition of humanity. Humanity is not a just biological category but a normative one too - it reflects changing philosophical and moral conceptions of ourselves. Today we are more uncertain than ever about what it means to be human. There is both anxiety about scientific pronouncements on human nature and fear that human progress and civilisation may be more forces for ill than for good. In an age that is unsure what humanity stands for, it makes sense to open the door and let everybody else join the club. The result is an anything fits humanity for an anything goes age.