From the book DENIAL: Self-Deception, False Beliefs, and the Origins of the Human Mind by Ajit Varki and Danny Brower. Copyright © 2013 by Ajit Varki. Reprinted by permission of Twelve/Hachette Book Group, New York, NY. All rights reserved.

The story behind this book is strange and improbable. Two individuals from very different backgrounds converged on a single question, happened to meet just once, discussed it briefly, parted company—and would never see each other again. One of them, Danny Brower, died suddenly at the age of fifty-five in 2007. The other person—I, a physician turned scientist—was left to complete our story. From our single chance conversation grew this book, which should interest anyone who cares about the universally human questions Who are we? How did we get here? Why are we the way we are? And where are we going?

The improbability of it all becomes starker when you consider what different circumstances the two of us came from. Danny was born in November of 1951, was raised in the United States, and worked his way up from modest means to the prestigious position of professor and chair of molecular and cellular biology at the University of Arizona at Tucson. By the time I met him, he was already well known for his pioneering work on protein molecules called integrins, which play key roles in how cells recognize and respond to their environment. Danny was using a popular fruit-fly model to study these processes, and from this same work, he was even able to contribute to our understanding of human cancer. As it turned out, Danny had another interest related to his research—he was fascinated by evolutionary biology, the study of the processes by which all life on this planet emerged over the last three billion years or so. A natural progression of such thinking made him wonder about the origin of our own species, Homo sapiens.

As for me, I was born just two months after Danny, but was raised on the other side of the planet, in India. I grew up in a traditional Orthodox Christian family from the southern state of Kerala, but attended English-language schools and went on to medical college with the idealistic goal of saving lives. But as it happens, the curriculum in medicine includes a strong dose of fascinating biology. Inspired by this aspect of my education, I finally decided that I could contribute more to society by becoming a biomedical researcher. However, opportunities to pursue this track in India were sparse in the 1970s. Reading the scientific literature, I realized that the United States was the one country in the world where physicians were being encouraged and supported in their efforts to do research side by side with other kinds of scientists. Thus it was that I emigrated to the United States in 1975 with six dollars and a suitcase, eventually becoming board certified in internal medicine, hematology, and oncology and working my way up to my present position as a professor at the University of California, San Diego (UC San Diego). Just as I had originally hoped, this career path allowed me to pursue my passion for science and research, and eventually took me away from patient care and into the emerging field of glycobiology, which studies the dense, complex, and varied forest of sugar chains that are now known to cover every one of the cells in our bodies. Technical difficulties in analyzing these “glycans” resulted in their getting limited attention in the early stages of the molecular biology revolution, which had focused mostly on DNA, RNA, and proteins. But we now know that these glycan chains are essential for life, and that they are involved in every normal and abnormal state of the body, from infections to cancer to brain development.

While starting up my independent research career I still continued to see patients part-time, as a physician and cancer specialist. The latter role naturally led me to ponder issues of life and death, particularly the question of how it was that patients with terminal cancer could so courageously fight to stay alive against all odds. It seemed to me that both patient and physician were actually denying the reality of what they were up against, even in the face of a grim prognosis. But then, optimistic thinking that helps us go on despite the odds doesn’t just feature in life-or-death situations; it is part and parcel of what makes us human, and comes across in so many of our activities. These and other life experiences, such as watching my own daughter grow up, made me wonder about how we became human, evolving away from a recent common ancestor with our closest living evolutionary cousins, the chimpanzees and other so-called great apes—gorillas, bonobos, and orangutans. Although great apes and humans look rather different, scientists as far back as in the 1960s and 1970s had shown that we are genetically very similar. In fact, viewed from the perspective of genes, we are more similar to chimpanzees than mice and rats are to each other! And chimpanzees have more in common with us genetically than they do with gorillas. So the big question has been: Why are we humans so different from chimpanzees and gorillas in appearance, behavior, and so many other features while they seem so similar to each other? Why is it that a chimpanzee or gorilla cannot do what I am doing right now—communicating with a reader about stories of past events with implications for our future? And although we may have never met each other, how is it that you, the reader, understand what I am thinking, and how do I know that you might be doing so?

In 1984, my thoughts about such matters were very suddenly brought into focus. I was seeing a patient who had an immune reaction to a horse serum that had been administered to treat a rare blood disease. What I learned from this case inspired additional research, and by the mid-1990s my research group had uncovered the first known clear-cut genetic difference between humans and great apes. In fact, scientists had been searching for two decades for genetic features that were uniquely different in humans, and I was lucky enough to find the very first example, the loss of a gene called CMAH , which had subtly but uniquely altered the cell surface sugars called sialic acids on all cells in the human body. Since then we have found several additional uniquely human changes in sialic acid biology that seem to contribute to the human condition, in health and disease. But that’s another story, for another time.

These unexpected findings stoked my already keen interest in something quite far removed from my original training—an explanation for the origins of the human species. Where we humans came from is undoubtedly one of our greatest unsolved mysteries, at least from the human perspective. And while the work of many scientists had painted the broad brushstrokes of how this might have happened, there was precious little known at the time about any molecules and biological processes unique to humans. So by the late 1990s I began to focus my research specifically on this area of anthropogeny (this classic but long-unused term encompasses the scientific pursuit of human origins and evolution). As you can imagine, this fascinating field of inquiry requires understanding of a rather wide range of subjects, many of which I was not trained in. But having achieved a modicum of scientific success and recognition in my primary research fields of medicine and glycobiology, I could now afford to devote more time to this new quest, immersing myself in other relevant specialties, such as primatology, evolutionary biology, neuroscience, linguistics, and anthropology. As part of this self-education quest, I began to seek advice from various experts in such fields, a process that eventually led to my forming (in 1996) an international transdisciplinary collaborative group of researchers interested in human origins and evolution. Supported primarily by the Mathers Foundation of New York, this group was recently expanded and renamed the Center for Academic Research and Training in Anthropogeny (CARTA). In this “center without walls,” affiliated with UC San Diego and the Salk Institute for Biological Studies, CARTA brings together academicians from the natural sciences, social sciences, and biomedical sciences along with interested parties from the humanities and arts, as well as contributors from the earth sciences, engineering, mathematics, and computing sciences. This first-of-its-kind effort assumes that definitive answers about the human origins mystery can best arise from breaking down traditional academic barriers and drawing experts from every relevant discipline into a creative transdisciplinary discussion. The core mission of CARTA is to “use all rational and ethical approaches to seek all verifiable facts from all relevant disciplines to explore and explain the origins of the human phenomenon.”

But let’s get back to the story of how I met Danny Brower. A decade into my quixotic quest to understand human origins and evolution, my own knowledge base was sufficient to embolden me to give a few public lectures on the topic. One of the first I delivered was at the University of Arizona on April 2, 2005, about molecular differences between humans and chimpanzees and how they might have contributed to human uniqueness. As you might imagine, I was a bit nervous. But the lecture seemed to go well, and audience responses were positive. At the pleasant spring open-air luncheon that followed, a tall, intense man with a scraggly beard sat down next to me, introduced himself as Danny Brower, and pointedly informed me that we were “all asking the wrong question.” At first I thought he was some local eccentric, but when I realized he was a well-known professor at the university, I gave him a careful hearing.

Instead of just asking what evolutionary processes made us human, Danny said we should also be asking why such complex mental abilities have appeared only in humans, despite many other intelligent species having existed and evolved for millions of years. In other words, if having complex humanlike mental abilities has been so good for the success of our species (as everyone has assumed), then how is it that we are the only species that got so brainy? The usual assumption is that something very unusual and special happened to human brains during evolution, and that we just need to find out what that something is. But Danny took a fascinating contrarian’s position, saying that we should not be looking for what everyone else was—the presumed special brain changes that made us human. Rather, we should be asking what has been holding back all the other intelligent species that, like humans, seem to have self-awareness of themselves as individuals—a list that may include chimpanzees, orangutans, dolphins, orcas (so-called killer whales), elephants, and even birds such as magpies. Danny asked: Why are there no humanlike elephant or humanlike dolphin species as yet, despite millions of years of evolutionary opportunity for making this transition?

The next mental step beyond the basic awareness of one’s own personhood that many of the species mentioned above seem to possess could be awareness of the personhood of others—in other words, knowing that others of your own kind are also equally self-aware. But Danny argued that gaining this useful ability would also result in understanding the deaths of others of your own kind—and, consequently , realizing one’s own individual mortality. And he suggested that this all-encompassing, persistent, terror-filled realization would cause an individual who first made that critical step to lose out in the struggle to secure a mate and pass his or her genes to the next generation—in other words, such an individual would reach an evolutionary dead end. Danny suggested that we humans were the only species to finally get past this long-standing barrier. And he posited that we did this by simultaneously evolving mechanisms to deny our mortality.

I suspect most readers will have the same initial reaction I had—that this seems much more convoluted and complicated than simply saying that we humans evolved special mental abilities over time. But I realized that Danny was describing an apparently novel theory based on a counterintuitive line of logic, which seemed relevant to explaining both human origins and some unique features of the human mind. And my decade-long self-education about human origins had already prepared me to consider the larger implications of what he was saying. I began to think that such a rare and difficult transition might even possibly explain why all humans on the planet today seem to have emerged from a small group in Africa, completely replacing all other humanlike species that coexisted at the time. I was genuinely intrigued and excited and we spent the next hour in deep conversation, even after most others had left the lunch table. Despite our widely disparate backgrounds and education, Danny and I had one important thing in common: our shared understanding of a basic fact of evolutionary biology—that unless you are able to pass on your genes to the next generation by generating progeny, it does not matter how successful you were during your life. So any new genetically based abilities can become permanently established in a species only if they contribute to this “reproductive fitness.”

The history of science is filled with ideas that initially went against conventional wisdom but were eventually proven to be true (such as Wegener’s theory of continental drift and Copernicus’s claim that the sun was the center of the solar system). So I was immediately attracted to Danny’s contrarian idea of looking not for what additional special features of our brains made us human—but rather asking what might have prevented other animals and birds from becoming humanlike in their mental functions. In other words, had we crossed a very difficult evolutionary barrier on the way to be- coming human? An analogy I later thought of was the process by which some ancient fishlike creatures moved from living in water to surviving on land. There were likely many attempts to make this transition, but evidence tells us that only a few such efforts actually succeeded. Apparently, several things had to happen at once, and in just the right order, to overcome this particular physiological evolutionary barrier. So why not also consider a psychological evolutionary barrier that blocks the path to humanlike awareness of reality? During our intense discussion I also asked Danny if religion could be the explanation for our success at overcoming that barrier, since all societies have religious belief systems and most religions provide explanations for what happens after death. He responded that while religion could have been a major factor that aided his proposed transition, it could not be the whole answer. After all, he said, do not most atheists live in constant terror of their own mortality? But he agreed that his theory could at least help explain the universality of religious belief systems in human societies. Most humans ask what lies beyond their death, and most religions provide an answer of some kind. There are also entire systems of philosophy that ask such existential questions, whether based on religious beliefs or not.

While there were obviously many details needed to support Danny’s unusual line of thinking, I was impressed by the basic concept, and suggested that he should publish it. But I also realized that, like me, Danny had no prior formal education regarding human evolution, and in the academic world he would not be considered qualified to officially opine on the subject. His interest had simply grown out of his knowledge of evolutionary biology combined with the innate desire most humans have to understand our own origins.

On the face of it, this was not a momentous encounter—a conversation of less than two hours between two scientists from very different backgrounds, each with a nonexpert interest in explaining human origins. But over the months that followed I simply could not shake the basic idea Danny had proffered. The more I continued with my own quest to learn about human origins within the multidisciplinary CARTA group I had formed, the more this idea seemed to make sense and to gain in potential significance. After two years of obsessing about my discussion with Danny, I finally looked up his e-mail address and sent a lengthy message in which I outlined my understanding of his basic theory, updating and adding various embellishments of my own and suggesting again that he should publish his concept. I was deeply disappointed not to hear back from Danny, but thought that I might not have the right e-mail address. A few months later I decided to look up his phone number on the Internet, and was shocked to instead find his obituary. Danny Brower died suddenly and unexpectedly in October of 2007 from a rare kind of blood vessel disease called aortic dissection (possibly resulting from a defect in connective tissue molecules—the very things he had studied in flies). On a day he was due to present a departmental seminar, he woke up with severe symptoms for the very first time and went into surgery that evening. Tragically, he never regained consciousness, and was declared brain dead four days later.

Once I got over the shock of this unexpected and sad news, I scoured the published literature to see if Danny had ever written about his idea, but I found no evidence that he had. One day soon thereafter I saw a dedication to Danny in a research article on an unrelated topic by a well-known scientist named Sean Carroll. I contacted Sean, who told me that Danny had in fact talked to him and to a few other friends about some of his ideas. Sean had even read and commented on some writings Danny had begun on the subject—efforts cut short by Danny’s untimely death. I was now even more convinced that the basic idea needed to be published. As it happened, I had previously gotten to know Philip Campbell, the editor in chief of the prestigious journal Nature , as he had once approached me to write an article about the ethics of doing research on great apes. I contacted Campbell and explained the situation. He was interested and suggested that I write a formal “letter to the editor” on the topic.

Before writing the letter, I spent more time reading the literature and grew to appreciate the importance of a psychological concept called “theory of mind”—also variously called mind-reading, attribution of mental states, perspective taking, mindsight, and multilevel intentionality. These jargonistic terms refer to various aspects of the human ability to go beyond self-awareness of our own minds to the full comprehension that other humans are also self-aware and have independent minds of their own—and to thus put ourselves into their mental shoes. For example, the reason I could have a discussion with Danny was that we both knew that the other had a mind capable of independent thought and reasoning. And by now, you, the reader, may have started developing a theory of mind about both of us authors, including the one who is not even alive today.

I also consulted learned colleagues from CARTA in relevant disciplines to determine whether Danny’s basic theory was truly original. It turned out that many other writers had already touched on the first half of the concept. Even ancient Indian Vedic texts had addressed the surprising fact that we humans deny the reality of our own mortality—easily—though we know its certainty. And in modern times, Ernest Becker’s Pulitzer Prize–winning 1973 book The Denial of Death emphasized the point further, suggesting that many aspects of human behavior and culture can be explained by this denial mechanism. But the second part of Danny’s idea—that the realization of our own mortality might have been a barrier to the emergence of a humanlike mind until our species was finally able to deny that realization—was unique; I found nothing like it in anything I read. I wrote the letter to Nature, and it appeared in August of 2009. The relevant sentences from the letter are reproduced below:

Among key features of human uniqueness are full self-awareness and “theory of mind,” which enables inter-subjectivity—an understanding of the intentionality of others. These attributes may have been positively selected because of their benefits to interpersonal communication, cooperative breeding, language and other critical human activities. However, the late Danny Brower, a geneticist from the University of Arizona, suggested to me that the real question is why they should have emerged in only one species, despite millions of years of opportunity. Here, I attempt to communicate Brower’s concept. He explained that with full self-awareness and inter-subjectivity would also come awareness of death and mortality. Thus, far from being useful, the resulting overwhelming fear would be a dead-end evolutionary barrier, curbing activities and cognitive functions necessary for survival and reproductive fitness. Brower suggested that, although many species manifest features of self-awareness (including orangutans, chimpanzees, orcas, dolphins, elephants and perhaps magpies), the transition to a fully human-like phenotype was blocked for tens of millions of years of mammalian (and perhaps avian) evolution. In his view, the only way these properties could become positively selected was if they emerged simultaneously with neural mechanisms for denying mortality. Although aspects such as denial of death and awareness of mortality have been discussed as contributing to human culture and behaviour, to my knowledge Brower’s concept of a long-standing evolutionary barrier had not previously been entertained. Brower’s contrarian view could help modify and reinvigorate ongoing debates about the origins of human uniqueness and inter-subjectivity. It could also steer discussions of other uniquely human “universals,” such as the ability to hold false beliefs, existential angst, theories of after-life, religiosity, severity of grieving, importance of death rituals, risk-taking behaviour, panic attacks, suicide and martyrdom. If this logic is correct, many warm-blooded species may have previously achieved complete self-awareness and inter-subjectivity, but then failed to survive because of the extremely negative immediate consequences. Perhaps we should be looking for the mechanisms (or loss of mechanisms) that allow us to delude ourselves and others about reality, even while realizing that both we and others are capable of such delusions and false beliefs.

Soon after the letter’s publication, I heard from Sheldon Solomon, a member of a well-regarded group of psychologists influenced by the ideas of Ernest Becker and best known for their “terror management theory.” Their concept is supported by various types of experimental evidence and indicates that we humans have a variety of “worldview and self-esteem mechanisms” to deal with the terror of knowing we are going to die. In his letter to me, Solomon wrote: “We agree with your argument that the benefits of consciousness and self-awareness could only be reaped if they were accompanied by simultaneous mechanisms to deny death.”

Thinking I had done my duty by getting Danny’s ideas to the attention of others who could pursue them, I turned my focus to aspects of anthropogeny that were more directly related to my own expertise in glycosciences and ape-human differences in biology. But then I received a very unexpected e-mail from Danny’s widow, Sharon Brower, who had been alerted to the Nature letter by one of Danny’s friends. Sharon thanked me for bringing her late husband’s unpublished idea into print, and told me that Danny had been spending all his spare time writing a book on the topic. Apparently, he had just completed his second draft before his sudden death. Ironically, while Danny had sometimes discussed plans for the distant future with Sharon, he also knew there was a possibility that he would die young: His own father had passed away suddenly at the age of fifty-six, of a heart attack. Danny’s thinking about his theory may have even caused him to be more aware of his own mortality. According to Sharon, this scared Danny a bit; he had always held up fifty-six as the age to surpass. Sadly, he died just a month short of that milestone birthday.

When Sharon sent me her late husband’s draft manuscript, I found that Danny not only had the core of an idea to explain the evolution of the human mind but that he also went on to present some important practical messages for humanity arising from his logic. He wrote that the human penchant to deny our mortality is but one manifestation of our overall ability to deny many other things—a propensity that has many ramifications, positive and negative. The manuscript was thoughtful and erudite, but it was clearly an incomplete effort that needed much additional research, expansion, and polishing, which Danny had been unable to do. With encouragement from Sharon, I therefore decided to continue the project by combining Danny’s original writing with my own, adding thoughts, ideas, and embellishments along the way.