Leonardo's Brain Read online

As I have done in my earlier books, I will capitalize the terms Natural Selection and Mother Nature. Also, I should explain where I locate myself on the spectrum of opinion regarding the role of genetics in determining evolution. At one end of the spectrum stand Stephen Jay Gould and Richard Lewontin, who propose that many traits, both physical and behavioral, are the result of Natural Selection’s random processes, and not too much should be read into them. They believe these genetic quirks neither help nor hinder the species.

  On the other end is the school headed by Jerome H. Barkow, Leda Cosmides, and John Tooby, which maintains that most of what is in the human genome is there to assist humans in surviving the vicissitudes of the environment to reach reproductive age and find a willing mate. If a mutation is deleterious to the survival and reproductive success of the species, it will be culled out of the genome within a few generations. If it is beneficial, it spreads throughout the species. Its rate of disappearance or multiplication depends on how much it is a winner or a loser. On the sliding scale of opinion, I align myself with this camp.

  I have poured myself into this book after reading an enormous amount of background information about Leonardo, the development of the brain, and the process of human evolution. I wanted to fulfill Franz Kafka’s pronouncement that a book should “be wielded like a pickaxe to shatter the frozen sea within the reader’s mind. If the book in our hands does not wake us, as with a fist that hammers on the skull, then it just isn’t worth reading.” I would prefer a similar, but less violent response. I want this book to stimulate thinking as I present a series of what I think are original theories. And I want it to be an enjoyable read. In writing this book I am attempting to live up to the two major ideals Leonardo set for the rest of us: to conjoin art and science, and to be bold when proposing hypotheses.

  Leonard Shlain

  Mill Valley, California

  March 2008

  Chapter 1

  Art/Science

  The good painter has to paint two principal things, that is to say, man and the intention of his mind. The first is easy and the second difficult, because the latter has to be represented through gestures and movements of the limbs—which can be learned from the dumb, who exhibit gestures better than any other kind of man.

  —Leonardo da Vinci

  The true mark of genius is not perfection, but originality, the opening of new frontiers; once this is done, the conquered territory becomes common property.

  —Arthur Koestler

  Both science and art form in the course of the centuries a human language by which we can speak about the more remote parts of reality; the coherent sets of concepts of physics and the styles of art are different visions that offset the language of words.

  —Werner Heisenberg

  Imagine that you are the chairperson of a hypothetical Nobel Prize committee that awards only one medal annually. The medal is given to an individual who has created not only a most extraordinary work of art, but who has also made a spectacular contribution to science. The competition would be open to any contemporary or historical figure, as well as the large swatch of humanity that lived before accurate biographical records were available.

  The divergent flow of art and science in the historical record provides evidence of a distinct compartmentalization of genius. The river of art rarely intersected with the meander of science. Despite the abundance of fantastic artists and brilliant scientists in human history, the stark monolithic fact is the dearth of candidates who could be considered for their contributions to both fields. Who, upon reflection, would you nominate to win the award in the field of both art and science?

  A disproportionate number of the short list of nominees would most likely emerge from the Italian Renaissance, a period when imaginative theories combined with experimental observation to form a solid basis for modern science, a development drastically reshaping society that intersected with equally innovative approaches to art. However, the historical record might be askew. For example, the twelfth-century Persian poet Omar Khayyam was the author of the acclaimed Rubaiyat. Lesser known is his towering reputation as a mathematician who advanced our ­knowledge of algebra.

  Because the concept of the individual is a relatively recent innovation, little is known of specific inventors and artists in many of the world’s cultures. We may never know if the Chinese scientific genius who invented the formula to glaze the delicate Sung Dynasty porcelain was also the same person who painted exquisite silk screens or composed deathless poetry. Poor record keeping and a pervasive cultural taboo against individuals taking credit for their personal contributions may have deprived many potential candidates from ever being recognized for their achievements in both art and science. The judges, however, must also entertain the very real possibility that no candidates exist during the majority of these relatively silent centuries.

  Those whom we could confidently propose would include the Renaissance architect, sculptor, and mathematician Leon Battista Alberti. His 1435 treatise on geometry and science that explained to painters how to place their figures in proper perspective would make him eligible as a scientist, and one can argue that his beautiful buildings are great works of art. Brunelleschi would surely appear on both lists. His skill in sculpture and his engineering brilliance in raising the dome of the cathedral Santa Maria del Fiore in Florence make him an attractive nominee. There would be no argument on granting the art prize to Michelangelo for his David, Pieta, and the Sistine Chapel. His solutions for many vexing architectural and engineering problems would ensure his scientific credentials as well. Architect Donato d’Agnolo, more commonly known as Bramante, would have a fair chance because of his buildings’ exceptional grace and the ingenious solutions he instituted in the field of math, geometry, and engineering.

  Galileo Galilei’s many towering scientific contributions would secure for him the science aspect of the medal. Less well known are Galileo’s masterful literary enterprises. He explained the intricacies of the scientific debates of his time in lucid prose that made accessible to the educated layperson the excitement of the Copernican ferment bubbling in seventeenth-­century Europe.

  After Renaissance Italy, the pickings, however, get progressively slimmer. Art and science begin to diverge. There are those who would posit that this was the result of the hyperinflation of knowledge in all fields of human endeavor. Johann Wolfgang von Goethe, the seventeenth-century German writer and poet, was one of the few who tried to breach both rapidly growing walls that increasingly separated art and science. He would surely get the nod for his contributions to literature, and his many investigative experiments advanced the progress of science.

  Sigmund Freud made many scientific discoveries, as well as the one for which he is the most famous: the founding of psychoanalysis. His attempt to discern the structure of the undercarriage of human consciousness would earn him his place as one of the titans of science. His voluminous writings, clear in tone and rich in imagery, could stand on their own for literary value, making Freud an attractive candidate for the award.

  Alas, upon closer scrutiny, the two committees conferring among each other would most likely arrive at a consensus for each of the above-named straddlers. The quality of their contributions in one or the other of the two fields did not meet the rigorous standards of a Nobel Prize. If they were known primarily as an artist, their contribution to the field of science would not quite attain the level of others who were first and foremost scientists. Similarly, if a candidate’s main field of endeavor was science, his or her artistic creations were not of the same order of quality as those of the artist contenders. Alexander Pope summed up this strange quandary when he wrote:

  One science only will one genius fit

  So vast is art, so narrow human wit.

  There is only one person who could handily win the prize in both categories: in art, for his innovative paintings, and in science, for the large number of principles he discovered and the plethora of technological inventions he envisione
d. This sui generis individual was Leonardo da Vinci.

  Evolution rarely produces only one of anything. There is no skill, trait, deformity, or clairvoyance that has not been observed in more than one individual. Child prodigy violinists, high school genius mathematicians, and preternaturally athletic sportsmen sporadically attract the public’s attention because of the rarity of their traits. But in every case, his or her talent, while extraordinary, was not so singular that there had never been anyone else who expressed the same talent with a similar degree of distinction.

  How, then, are we to explain the fact that in all of history Leonardo occupies a solitary niche? His uniqueness has continued to enthrall commentators throughout the nearly five centuries that have followed his death in 1519.

  As the 500th anniversary of his death approaches, the pace of interest in Leonardo is actually accelerating. A veritable army of PhD specialists has pored over Leonardo’s chaotically organized manuscript pages, translating, collating, and trying to discern what this restless mind has to say to the rest of us. Art critics continue to tease out of his oeuvre so many new and unexpected details; it hardly seems possible the mind of one man could have considered so many factors in planning and making his art, while at the same time immersing himself in myriad scientific pursuits.

  Although both art and science require a high degree of creativity, the difference between them is stark. For visionaries to change the domain of art, they must make a breakthrough that can only be judged through the lens of posterity. Great science, on the other hand, must be able to predict the future. If a scientist’s hypotheses cannot be turned into a law that can be verified by future investigators, it is not scientifically sound. Another contrast: Art and science represent the difference between “being” and “doing.” Art’s raison d’être is to evoke an emotion. Science seeks to solve problems by advancing knowledge. Candace Pert reminds us that in spite of our curiosity about science, we call ourselves, “human beings, not human doings.”

  In the realm of science, pure mathematics comes the closest to art in that it often does not have any practical application in the real world. Artists and mathematicians extol the virtues of beauty and elegance. In his classic, A Mathematician’s Apology, G. H. Hardy wrote, “Beauty is the first test; there is no permanent place in the world for ugly mathematics.”

  Leonardo’s story continues to compel because he represents the highest excellence all of us lesser mortals strive to achieve—to be intellectually, creatively, and emotionally well-rounded. No other individual in the known history of the human species attained such distinction both in science and art as the hyper-curious, undereducated, illegitimate country boy from Vinci.

  With so much already written about this singular man, it seems presumptuous to fell another tree in the vainglorious attempt to understand his genius. Yet, I propose to undertake this project from a somewhat unorthodox point of view. I venture into the Leonardo thicket with the intent to reemerge having reconstructed the physical configuration of Leonardo’s brain by performing, what will be, in essence, a posthumous brain scan.

  Hidden in the historical record is a veritable gold mine of unusual clues regarding Leonardo’s brain function. Leonardo was a left-handed, ambidextrous male. He is the only historical figure whom we know wrote backward. Some biographers believe that Leonardo was a gay male who did not indulge his sexual passions. He was both a composer and musician, and spoke and wrote several different languages.

  We also have a report that he suffered a stroke in his last years that paralyzed his right hand. The reliable observer who recorded this most telling piece of the Leonardo brain puzzle also informs us that because of this infirmity, the master gave up painting and instead devoted his last years to his scientific investigations. This brief catalog of Leonardo’s neurological features provides a wealth of information from which to begin a speculative analysis concerning the structure of his brain and its unique wiring diagram (his neurocircuitry) that fueled so much of his creativity.

  Other tantalizing enigmas concerning the organization of Leonardo’s nervous system abound. His neurological peculiarities emerge from the comprehensive historical record detailing his life. (And what a historical record!) Leonardo was a recognized genius during his lifetime, prompting many contemporaries to record their impressions of him. Also, we have a treasure trove from his own hand, with over five thousand pages of his manuscripts remaining. Despite his prodigious urge to scriven, he never managed to publish.

  The same maddening pattern to leave projects unfinished also bedeviled his art. He left posterity with some fifteen paintings that we are sure came from all (or part) of his hand. None of his many sculptures and nothing of his musical compositions survive. Fortunately, much is known of many of these works because contemporaries who did see (or hear) them felt compelled to describe them in considerable detail. Also, his notebooks contain hundreds of preparatory sketches for later major works. Moreover, Leonardo’s lost masterpieces so impressed many excellent artists—who had the opportunity to view them before they were destroyed, misplaced, or altered—that they reproduced faithful copies of Leonardo’s originals.

  Besides his paintings, thousands of Leonardo’s drawings remain extant. Many of these were preparatory sketches for his later paintings, and thus provide valuable insights into his creative process. His numerous notes and drawings concerning his vast interest in science contain similar insights into how his mind worked, even if the many actual inventions and devices he made have not survived.

  Though his notebooks don’t reveal many—if any—close female relationships, one shouldn’t assume Leonardo had no knowledge or appreciation of the female. In fact, if one contemplates Leonardo’s paintings and drawings, an entirely different impression emerges. Has there ever been a male artist who more deftly depicted the enigma of a woman’s smile, the love of a mother for her child, or the self-confidence of a beautiful woman posing for a famous painter? How is it possible that one man could have coaxed out of mere paint the most subtle secrets of the feminine and yet not bother to allude to any of those revelations in ink, much less mention that he even knew any women? Quite to the contrary, a number of misogynist remarks mar his writings.

  Leonardo was a vegetarian in a culture that thought nothing of killing animals for food. His explanation for his unwillingness to participate in carnivory was that he did not want to contribute to any animal’s discomfort or death. He extended the courtesy of staying alive to all living creatures, and demonstrated a feeling of connectedness to all life, which was in short supply during a time that glorified hunting.

  Another paradox: No other artist in history expended as much time and energy working out the geometrical details of the science of perspective. Page after page of his various codices contain intricate drawings that recursively return to the problems perspective posed to the artist. He gives precise instructions to painters on how they should depict the penumbra of shadows and how to position objects relative to each other in a composition so that the laws of perspective are rigorously followed. How, then, do we explain the unsettling discovery—when carefully examining Leonardo’s paintings—that he cleverly violates the laws of perspective in all of them? These anomalies will be detailed in a later chapter. Leonardo is both an extraordinary left-brained academician obsessed with portraying perspective correctly and an impish right-brained trickster who takes delight in fooling the viewer with perspectivist sleights of hand.

  An observer glancing back and forth between Leonardo’s art and his notes would begin to suspect that the hand directing his pen did not seem to know what the hand holding his brush was doing, and vice versa. After poring over his voluminous notes and then studying his paintings, a neuroscientist most likely would conclude that only the paltriest of fiber bundles connected the two hemispheres of his brain. Yet, this neurological assessment regarding the status of Leonardo’s corpus callosum—the broad band of fibers that connects the brain’s two halves—would fly in the fa
ce of what we know about his left-handedness, which in turn is a fairly accurate predictor of hemispheric dominance. Leonardo was the rare writer who routinely engaged in reverse writing, or mirror writing. Someone wishing to read Leonardo’s manuscripts must first hold the pages before a mirror. Instead of writing from left to right, which is the standard among all European languages, he chose to write from right to left—what the rest of us would consider backward writing. And he used his left hand to write.

  Thoroughly confusing the issue was the fact that sometimes he would switch in mid-sentence, writing some words in one direction followed by other words heading in the opposite direction. Another intriguing neurological datum: Careful examination of two samples of his handwriting show the one written backward moving from right to left across the page is indistinguishable from the handwriting that is not reversed.

  Leonardo’s quirks of penmanship strongly suggest that his two hemispheres were intimately connected in an extraordinary way. The traditional dominance pattern of one hemisphere lording it over the other does not seem to have been operational in Leonardo’s brain. Based on what we can extrapolate from the brains of people who share Leonardo’s ability to mirror-write, the evidence points to the presence of a large corpus callosum that kept each hemisphere well informed as to what the other was doing.

  Another suggestive piece of evidence that Leonardo’s corpus callosum was fairly bursting with an overabundance of connecting neurons was his seamless annealing of art and science. Numerous neurological studies have, in general, located the modules primarily concerned with art, music, imagery, metaphor, emotion, harmony, beauty, and the aesthetic sense of proportion in the right hemisphere of a right-handed person. Housed in the left hemisphere of a right-handed person are the skills required to carry out the logical, linear, sequential analysis necessary for grammar, syntax, reason, and mathematics. A neuroscientist, examining a subject who had harmonized the very different functions of art and science, would expect that an individual so endowed would possess an exceptionally robust corpus callosum. How, then, do we square these latter facts of hemispheric integration with the earlier observations of the seemingly apparent disconnect between the content of Leonardo’s written words and the iconic imagery of his art? These neurological puzzles are just a few that I will try to decipher in my attempt to crack Leonardo’s brain code.