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The Dragons of Eden, a Pulitzer Prize winning novel written by the renowned astronomer Dr. Carl Sagan, was first published in 1977 by Random House publishing company, located in New York City. The book is 275 pages in length, including 25 pages of bibliography, glossary, and index.
Carl Sagan (1934-1996) is perhaps one of the most celebrated scientific authors of the 20th century. During his lifetime, he published hundreds of scientific papers and either authored or co-authored more than 20 books, including Cosmos, the best selling science book ever to have been published in English. Dr. Sagan also hosted the popular PBS series "Cosmos," seen by 500 million people in 60 countries. He won several prestigious scientific awards, including the NASA Apollo Achievement Award, the Public Welfare Medal (the highest award of the National Academy of Sciences), and 18 honorary degrees from several American universities. He held the David Duncan chair as professor of Astronomy and Space Sciences at Cornell University, where he also acted as the Director of the Laboratory for Planetary Studies.
In addition to astronomy, Dr. Sagan was also very interested in various biological topics such as the origins of life and human evolution. In the 1950s, he assisted the Nobel Prize-winning geneticist H. J. Muller in his research on the origins of life. Sagan received the Masursky Award from the American Astronomical Society for his contributions to the project. The award states that, "as a scientist trained in both astronomy and biology, Dr. Sagan has made seminal contributions to the study of planetary atmospheres, planetary surfaces, the history of the Earth, and exobiology." In 1978 he won the Pulitzer Prize for The Dragons of Eden, his first novel regarding evolution.
The Dragons of Eden principally concerns the evolution of human intelligence and cognition. Under this main theme, Sagan discusses quite a wide variety of subtopics, ranging from brain to body mass ratios to an explanation of why we dream. He does not present an overall thesis, but rather several smaller theories, many of which he supports with a great deal of logic and experimental evidence.
In order to allow readers to gain a proper perspective on their own history in respect to the nearly incomprehensible history of the universe, Sagan provides a cosmic calendar at the beginning of chapter one. The calendar divides the entire history of the universe (approximately 12 billion years) into a single year. According to the calendar, the Big Bang occurred on the first second of January 1st, the Earth was formed on September 14th, and the first humans appeared on December 31st. It is perhaps very humbling to realize that, as a species, humans have only existed for a very small amount of time compared with the history of the universe. Our entire modern culture has existed for less than one second: the very last second of the comic year.
Genes and Brains
Chapter two, titled "Genes and Brains," discusses, to a large extent, the relationship between brain to body mass ratio and intelligence. Perhaps not surprisingly, humans have the largest brain to body mass ratio at about 12%, followed by dolphins and non-human primates. Sagan contends that brain mass is only related to intelligence when the mass of the brain is less than one kilogram. Above this threshold, brain mass does not seem to have a statistically significant effect on intelligence. He provides the example of two men, Lord Byron and Anatole France, both of which exhibited above average intelligence. Lord Byron's brain however, weighed 2,200 grams, while Anatole France's weighed only 1,100 grams. It appears that a mass difference of 1.2 kg does not have a significant effect on intelligence. However, microcephalics, individuals born with very small brains, usually have a brain mass of 450 - 900 grams (in comparison, chimpanzees have an average brain mass of about 500 grams). Their mental capabilities are drastically reduced compared with an average human, indicating that there exists a correlation between brain mass and intelligence below 900 - 1000 grams.
The Brain and the Chariot
Chapter three, "The Brain and the Chariot," concerns the anatomical evolution of the human brain. Carl Sagan conceptualizes the human brain as three main evolutionary components: the R-complex, the limbic system, and the neocortex. The R-complex is considered the most basic and primal part of the brain, having evolved hundreds of millions of years ago. In fact, humans share the R-complex region with all other mammals and reptiles. It plays an important role in aggressive behavior, territoriality, ritual, and social hierarchies. Physiologically, it is involved in some of the most basic brain-regulated functions, such as breathing and control of heart rate. The limbic system, which encapsulates the R-complex, evolved around 150 million years ago, and is fully developed only in mammals. The limbic system is responsible for the strong and vivid emotions that are most often associated with humans, but are also characteristic of other primates and mammals. The newest region of the brain, having evolved only 10 million years ago, is the neocortex. The neocortex is only found in the "higher" mammals, including primates and humans. All advanced brain functions, including language, anticipation, vision, and fine motor skills, are processed and controlled by the neocortex.
The Tribune Brain
Within this chapter, Carl Sagan provides one of his major evolutionary theories, which concerns the existence of the triune brain (composed of the R-complex, limbic system, and neocortex). He believes that the triune brain exists because the loss of any one of the more ancient complexes (mainly the R-complex and limbic system) would have resulted in death. Evolution of brain structure could only be accomplished "by the addition of new systems on top of old ones." Crucial to survival, each of the pre-existing systems would have to be preserved for any successful advancement to be made. For instance, if one of our primate ancestors were born with a very large and well-developed neocortex, but an under-developed or non-existent R-complex, that individual would have died instantly, having had no chance to pass on its large neocortex genes to the next generation. Thus the brain of the modern human still contains some the basic structures found in other mammals, reptiles, and even fish.
The Garden of Eden
The next three chapters deal primarily with the ideas behind the title of the book, in which Eden is used as a metaphor for the early evolution of man. This is perhaps the most interesting and brilliant part of the book, in which Carl Sagan describes the impact of a rapidly developing neocortex, and the evolutionary forces that shaped the modern human mind. Eden, as used in this metaphor, is literally the temporal span of approximately three to four million years ago in which our ancestors, including members of the genus Homo, were "perfectly interwoven with the other beasts and vegetables."
During this period of time, or Eden, the human prefrontal lobes evolved quite rapidly, allowing for the development of anticipation, and consequently the knowledge of death. There is evidence that Neanderthals, a close "cousin" of Homo sapiens, conducted burial ceremonies that included the placement of jewelry and flowers with the deceased. This suggests that Neanderthals were not only aware of death, but they were capable of developing complex rituals to sustain the deceased in the afterlife. Sagan wrote: "It is not that death was absent before the spectacular growth of the neocortex, before the exile from Eden; it is that, until then, no one had ever noticed that death would be his destiny." The relatively rapid evolution of the human brain over the last few million years, Sagan contends, was driven by a selection process that required cooperative interaction between the motor cortex and neocortex. The development of the motor cortex was necessary for our ancestors to throw projectiles accurately, move with agility, and outrun both prey and predators. It is likely that modern sports, as well as strategic games such as chess and warfare, exist today as a result of our "pre-wired hunting skills," which, for our ancestors, often meant the difference between life and death. A large neocortex was also highly selected for, as it allowed for the development of communication via gestures and eventually verbal language. Early humans, having evolved on the plains of Africa, were faced with many large and dangerous animals. In order to successfully stalk and immobilize their prey, it would have been necessary for hunters to communicate with one another using at least a simple symbolic language. Individuals and groups that could communicate better, move faster, and formulate more effective attack strategies had the greatest chance of survival (and consequently were able to pass their genes on to subsequent generations).
Why do we Sleep?
Chapter six, "Tales of Dim Eden," tackles the question: why do we sleep? The role of sleep as a survival mechanism is not as defined as those of fine motor skills or linguistic abilities. It is a trait humans share with nearly every mammal and bird, yet its function is very poorly understood. Sleep seems to defy natural selection, as individuals who are asleep tend to be easy prey. But Sagan suggests that, during the early evolution of mammals, sleep may have actually decreased their vulnerability by immobilizing them during periods in which they were most vulnerable to predatory reptiles. In regard to the evolution of human intelligence, Carl Sagan believes that sleep may have played a much more complex role. He asserts that the manifestation of dreams during REM (random eye movements) sleep allows the artistic right hemisphere to briefly take control of the more logical, linguistic left hemisphere (which is used to a greater extent during the day). This is perhaps an essential exercise for the right hemisphere, which is largely responsible for insight and innovation. In addition, Sagan believes that dreams may be a way to process thoughts and emotions perceived during the day's experiences, allowing for the organization and storage of information into short and long term memory. The ability to innovate (allowing the development of new tools, hunting techniques) and properly store and retrieve memories would have been highly beneficial to the survival of early humans.
Future Evolution of the Human Brain
The last chapter of the book discusses the future evolution of the human brain. Sagan contends that it is unlikely that the brain will become much larger than it currently is due to the limitation imposed by the female pelvis and birth canal. In the future, however, technology may allow for the full-term development of a fetus outside of the uterus, which would permit larger brain volumes. It is more likely, however, that we will simply use technology to improve the brain that evolution has "provided" us with thus far. The implantation of microprocessors or other artificial devices could drastically improve several cognitive abilities, including memory and mathematics. Likewise, it may be possible to accurately impair those components of the brain "that may be responsible for some of the perils and contradictions facing mankind." The Dragons of Eden is simply one of the best books I have ever read, scientific or otherwise. Despite the introduction of multiple theories in nearly every chapter, Carl Sagan manages to support each one clearly and convincingly. In addition to his own theories, many of which he synthesizes from a wide array of evidence, he also presents the theories of other scientists, even those that contract his own. I found this aspect of the book especially refreshing, as it embodies the true spirit of scientific inquiry. In addition, Sagan presented ideas and insights that I had never considered before. His theories on the triune brain and evolutionary purpose of dreams were especially intriguing.
The only shortcoming of the book is perhaps its age; having been published 25 years ago, it lacks new evidence and experimental findings. For example, in 1977 the overwhelming evidence that the impact of a large asteroid was responsible for the extinction of the dinosaurs did not yet exist. As a result, Sagan presented the out-dated supernova extinction theory, in which the explosion of a distant star destroyed the ozone layer, allowing radiation to penetrate the surface of the Earth. In addition, studies using new technological innovations such as PET and MRI scans of the brain are obviously not covered, as these devices were not available at the time. The lack of modern evidence, however, is not detrimental to most of the theories and ideas presented in the book. Sagan's extrapolations and insights into the development of human intelligence remain both relevant and indisputably fascinating.
In conclusion, what Carl Sagan has done in The Dragons of Eden is no less than compose a beautiful and intricate portrait of our cognitive past. For a well written, and surprisingly entertaining overview of the evolution of human intelligence, The Dragons of Eden is most highly recommended.
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