The goals of the Decade of the Brain were necessarily more open-ended, but still the PET scanner, and the yet more sophisticated brain imaging techniques that followed in its wake, had more than fulfilled their promise, allowing scientists to draw another exquisitely detailed map locating the full range of mental abilities to specific parts of the brain. There were many surprises along the way, not least how the brain fragmented the simplest of tasks into a myriad of different components. It had long been supposed, for instance, that the visual cortex at the back of the brain acted as a sort of photographic plate, capturing an image of the external world as seen through the eye. But now it turned out that the brain ‘created’ that image from the interaction of thirty or more separate maps within the visual cortex, each dedicated to one or other aspect of the visual image, the shapes, colour, movement of the world ‘out there’. ‘As surely as the old system was rooted in the concept of an image of the visual world received and analysed by the cortex,’ observes Semir Zeki, Professor of Neurobiology at the University of London, ‘the present one is rooted in the belief that an image of the visual world is actively constructed by the cerebral cortex.’
Steven Pinker, Professor of Brain and Cognitive Science at the Massachusetts Institute of Technology, could explain to the readers of Time magazine in April 2000 (the close of the Decade of the Brain) how neuroscientists armed with their new techniques had investigated ‘every facet of mind from mental images to moral sense, from mundane memories to acts of genius’, concluding, ‘I have little reason to doubt that we will crack the mystery of how brain events correlate with experience.’
Both the Human Genome Project and the Decade of the Brain have indeed transformed, beyond measure, our understanding of ourselves – but in a way quite contrary to that anticipated.
Nearly ten years have elapsed since those heady days when the ‘Holy Grail’ of the scientific enterprise, the secrets of life and the human mind, seemed almost within reach. Every month the pages of the science journals are still filled with the latest discoveries generated by the techniques of the New Genetics, and yet more colourful scans of the workings of the brain – but there is no longer the expectation that the accumulation of yet more facts will ever provide an adequate scientific explanation of the human experience. Why?
We return first to the Human Genome Project, which, together with those of the worm and fly, mouse and chimpanzee and others that would follow in its wake, was predicated on the assumption that knowledge of the full complement of genes must explain, to a greater or lesser extent, why and how the millions of species with which we share this planet are so readily distinguishable in form and attributes from each other. The genomes must, in short, reflect the complexity and variety of ‘life’ itself. But that is not how it has turned out.
First, there is the ‘numbers problem’. That final tally of twenty-five thousand human genes is, by definition, sufficient for its task, but it seems a trifling number to ‘instruct’, for example, how a single fertilised egg is transformed in a few short months into a fully formed being, or to determine how the billions of neurons in the brain are wired together so as to encompass the experiences of a lifetime. Those twenty-six thousand genes must, in short, ‘multi-task’, each performing numerous different functions, combining together in a staggeringly large number of different permutations.
That paucity of genes is more puzzling still when the comparison is made with the genomes of other creatures vastly simpler than ourselves – several thousand for a single-cell bacterium, seventeen thousand for a millimetre-sized worm, and a similar number for a fly. This rough equivalence in the number of genes across so vast a range of ‘organismic complexity’ is totally inexplicable. But no more so than the discovery that the human genome is virtually interchangeable with that of our fellow vertebrates such as the mouse and chimpanzee – to the tune of 98 per cent or more. There is, in short, nothing to account for those very special attributes that so readily distinguish us from our primate cousins – our upright stance, our powers of reason and imagination, and the faculty of language.
The director of the Chimpanzee Genome Project, Svante Paabo, had originally anticipated that its comparison with the human genome would reveal the ‘profoundly interesting genetic prerequisites’ that set us apart:
The realisation that a few genetic accidents made human history possible will provide us with a whole new set of philosophical challenges to think about … both a source of humility and a blow to the idea of human uniqueness.
But publication of the completed version of the chimpanzee genome in 2005 prompted a more muted interpretation of its significance: ‘We cannot see in this why we are so different from chimpanzees,’ Paabo commented. ‘Part of the secret is hidden in there, but we don’t understand it yet.’ So ‘The obvious differences between humans and chimps cannot be explained by genetics alone’ – which would seem fair comment, until one reflects that if those differences ‘cannot be explained’ by genes, then what is the explanation?
These findings were not just unexpected, they undermined the central premise of biology: that the near-infinite diversity of form and attributes that so definitively distinguish living things one from the other must ‘lie in the genes’. The genome projects were predicated on the assumption that the ‘genes for’ the delicate, stooping head and pure white petals of the snowdrop would be different from the ‘genes for’ the colourful, upstanding petals of the tulip, which would be different again from the ‘genes for’ flies and frogs, birds and humans. But the genome projects reveal a very different story, where the genes ‘code for’ the nuts and bolts of the cells from which all living things are made – the hormones, enzymes and proteins of the ‘chemistry of life’ – but the diverse subtlety of form, shape and colour that distinguishes snowdrops from tulips, flies from frogs and humans, is nowhere to be found. Put another way, there is not the slightest hint in the composition of the genes of fly or man to account for why the fly should have six legs, a pair of wings and a brain the size of a full stop, and we should have two arms, two legs and that prodigious brain. The ‘instructions’ must be there, of course, for otherwise flies would not produce flies and humans humans – but we have moved, in the wake of the Genome Project, from assuming that we knew the principle, if not the details, of that greatest of marvels, the genetic basis of the infinite variety of life, to recognising that we not only don’t understand the principles, we have no conception of what they might be.
We have here, as the historian of science Evelyn Fox Keller puts it:
One of those rare and wonderful moments when success teaches us humility … We lulled ourselves into believing that in discovering the basis for genetic information we had found ‘the secret of life’; we were confident that if we could only decode the message in the sequence of chemicals, we would understand the ‘programme’ that makes an organism what it is. But now there is at least a tacit acknowledgement of how large that gap between genetic ‘information’ and biological meaning really is.
And so, too, the Decade of the Brain. The PET scanner, as anticipated, generated many novel insights into the patterns of electrical activity of the brain as it looks out on the world ‘out there’, interprets the grammar and syntax of language, recalls past events, and much else besides. But at every turn the neuroscientists found themselves completely frustrated in their attempts to