I can hardly count the number of times when, browsing around in second-hand bookshops, my eye has been caught by a book entitled Left Hand, Right Hand! Disappointment, however, always followed. Instead of what I had hoped to find, a book about why our right and left hands are so different, I had actually found the first volume of the autobiography of the English writer, Sir Osbert Sitwell. It said little about what I was looking for. With my present title, I hope I may satisfy those few others who have perhaps also looked for that seemingly elusive book about our two hands and sides - a book that explores why the world, indeed the universe, so ubiquitously but so seemingly irrationally seems full of asymmetries.
Sitwell called his autobiography Left Hand, Right Hand! 'because, according to the palmists, the lines of the left hand are incised inalterably at birth, while those of the right hand are modified by our actions and environment, and the life we lead'. It is an intriguing statement, with its mixture of a very modern emphasis on the twin roles of genes and environment in shaping our lives, and the reference to palmistry, which most scientists would immediately reject, and which has components of the universal symbolisms attached to left and right. Sitwell, himself, is certainly not so gullible as to see the idea as anything other than a loose metaphor, and although he acknowledges that Tbelieve all men, including myself, to be superstitious', he does reject 'the childish boundaries of chiromancy'.
From our present perspective, we do not need seriously to ask whether such a claim has any empirical truth in it, but it can nevertheless act as a starting point for asking how our hands actually do differ. We can also see it as part of that vast repertoire of symbolism associated with right and left, which permeates so much of our daily lives, from the political left and right wing, through dexterity and 'cack-handedness', to 'lefthanded marriages'. If we do have such symbolisms, why do we have them? Is it perhaps because our hands are so asymmetrical, or because our hearts are asymmetric, or even because the universe in which we live is asymmetric? These are wonderfully deep questions, which will take us into many and varied aspects of social life and anthropology, and into the workings of the brain and the subtleties of human language. They will require us to look at our asymmetric bodies, with their asymmetric heart, liver, stomach, kidneys and even testicles; down into the amino acids and sugars, the building blocks of our body, which are also asymmetric; and, finally, into the asymmetries of physics itself, and hence of the universe.
In his introduction to Left Hand, Right Hand! Sitwell muses that, 'Already I am nearing fifty and the grey hairs are beginning to show, I have reached the watershed and can see the stream which I must follow downhill towards the limitless ocean, cool and featureless. It is time to begin.' My own grey hairs have long been apparent, and I have been studying and researching, some would say obsessing, about handedness and lateralisation since my first paper on the subject in 1972. The interest has never gone away - the questions, in fact, becoming ever more interesting - and the interest of others has continued similarly to grow. Half a dozen times a year, I am phoned by radio and TV producers who have suddenly noticed that ten per cent of their audience is left-handed and who therefore thought it would be an exceedingly novel idea to do a programme on left-handedness. When I do those interviews, the same old questions are asked and much interest is shown, but there is little time to provide proper answers. I hope here that I have provided broader answers for those audiences, who will realise that the field is far too interesting to be crammed into ten minutes. In recent years, there have been all sorts of advances, in everything from molecular asymmetries, through anatomy and developmental biology, to neuroscience, psychology, anthropology, sociology, and even cosmology. It is time, therefore, to take stock. Even if I am uncomfortably aware that I am not an expert in even a fraction of the requisite areas, I can claim to be an enthusiast.
If I have perhaps climbed high enough into the mountains to see over many terrains, I hope I have still not yet reached that col, that saddle point, that watershed, which Sitwell described from where one can only gently descend to the distant ocean. The terrain to be covered by this book is varied; sometimes rocky and thorny, and occasionally sufficiently dense to make impossible any distant perspective. A brief map of the territories to be travelled may therefore be helpful. Chapter 1 begins with the nineteenth-century case history of a patient, John Reid, who had his heart on the right side of his body. As was realised by Dr Thomas Watson- a now somewhat neglected figure whose reputation deserves rehabilitation - explaining why the heart is usually found on the left is extremely difficult. Watson realised that it is even more difficult to account for why John Reid should also have been right-handed rather than left-handed. Two other great nineteenth-century discoveries - Pasteur's demonstration that the molecules in living organisms are asymmetric, and Dax and Broca's finding that language is usually in the left half of the brain - set the scene for the rest of the book. Chapter 2 stands back and surveys the near-universal human interest in right and left, and the left-right symbolism that seems to be found in all cultures, underpinning many of the phenomena encountered in this book. Chapter 3 looks at Kant's problem concerning the philosophical difficulties of describing left and right, and chapter 4 considers how the words 'left' and 'right' have evolved in various languages, exploring, in particular, why so many people have problems in using these terms consistently and without confusion. Chapter 5 returns to Watson's problem of why the heart should be on the left, setting this in the broader biological perspective of why bodies are usually symmetric and how the gross asymmetry of the heart could have evolved. Chapter 6 digs more deeply into the sub-microscopic details of biology, looking at the asymmetry of molecules, in particular the amino acids, and considers how such asymmetries could have arisen either from sub-atomic physics or in the cold wastes of interstellar space. Chapter 7 returns to a more mundane level, looking at right- and left-handedness in their everyday sense, and describing a genetic model that accounts for how handedness is inherited and runs in families. Chapter 8 looks at the asymmetry of the brain, considering both the typical language-related processes that occur in the left hemisphere, and the more holistic functions of the right hemisphere, as well as the ways in which the two sides work together to carry out complex psychological processes. Chapter 9 concludes the section on handedness by asking about historical and cross-cultural differences in the rate of right- and left-handedness. It looks at archaeological evidence for right-handedness in early hominids, and its absence in apes and other animals, and then asks what the underlying difference is between the left and right hemispheres of the brain. Chapter 10 is about how social interactions are important in determining such lateralised behaviour as the direction of writing (from left to right in the case of English), or driving on a particular side (such as the left in Britain), or the relative advantage of left-handers in the ritualised fighting of sport. Chapter 11 considers the social processes that influence what it is like to be in the left-handed minority of a society in which most people are right-handed, and the effects on language, perception and stigmatisa-tion. Chapters 12 and 13 are diversions that nonetheless have their deeper aspects; those in chapter 12 looking at some of the many errors that haunt much thinking about lateralisation and the many fictions that have resulted from these concerning left and right, whereas chapter 13 is unashamedly lightweight: a collection of handedness trifles, trivia and miscellanea, some fun, some amusing, but hopefully all instructive in their way. Chapter 14 returns to the more solid substance of the book but instead of looking at asymmetry it considers the thus far neglected concept that has lurked behind so much discussion of asymmetry, and that is so central to scientific theorising - symmetry. In a finale to the book, chapter 15 argues for the triumph of asymmetry over symmetry and proposes a single picture of asymmetries, from the sub-atomic, through the biochemical and the anatomical, to the neurological, the cultural and the social.
Since I am an academic, I wrote footnotes and endnotes in profusion while preparing this book, not least so that I could defend and justify some tricky points to my ever critical colleagues. I did, though, remember the words of Toby Mundy suggesting that popular science books should be 'scholarly but not academic'. The notes allowed me to be an academic and also to wander off into some arcane backwaters. In the interests of space and the reader's patience, however, many of these have been stripped from the book, much as one takes down the scaffolding after building a house. Some of those deleted may be of interest to the occasional reader. In the notes at the end of the book I have therefore included the symbol wwwwa to indicate a more extensive note, a hypernote, which can be accessed on the Internet. The site to look for is www.righthandlefthand.com. This website also has additional material, and offers the opportunity to take part in experiments and research studies.