Dragons of Eden: Speculations on the Evolution of Human Intelligence Review
While I wrote this review for one of my Cognitive Science courses, it holds a special place in my heart. The book, 'Dragons of Eden: Speculations on the Evolution of Human Intelligence' was the first Cognitive Science text I ever read. This book truly sparked my interest in Cognitive Science and was the primary influence on my choice of major. Special thanks to Carl Sagan for being the most captivating and inspiring nonfiction writer I've yet to read the works of.
April 27, 2020
Dragons of Eden: Speculations on the Evolution of Human Intelligence Review
Carl Sagan’s “Dragons of Eden: Speculations on the Evolution of Human Intelligence” is not just a Pulitzer prize-winning book, but an insight into the development of mankind. This controversial, but introspective view of the development of what truly separates mankind. The book dives into the evolution of human intelligence through the physical evolution of the brain, the external factors influencing how intelligence is developed, and how intelligence varies between species. It’s a book based on anthropology, neuroscience, psychology, biology, linguistics, and computer science which offers an interesting perspective on what it means to be human. The book discusses four main topics, the Triune brain, the metaphor of Eden, the measure of intelligence, and the destruction of other potentially intelligent species.
Sagan devotes much of Dragons of Eden to discuss the first topic, the “triune” brain. The triune brain is a model of the evolution of the brain proposed by the American physician and neuroscientist Paul D. MacLean where the brain is divided into three sections which were sequentially added to the brain in the course of evolution. The first brain is the Reptilian complex, which controls primal urges and is shared with our reptilian ancestors. The second brain is the Paleo-mammalian complex which controls more emotional urges and is shared with all mammals. The last, outer brain is the Neo-mammalian complex. This is found primarily in humans and is linked with “high-level cognitive abilities” like abstract planning, tool-making, language, and self-awareness.
The Reptilian complex is essentially the Basal Ganglia, otherwise known as the brain stem. The brain stem controls the language of body sensations, impulses, and instinctive responses, as well as controlling basic body functions. The Paleo-mammalian complex is essentially the Limbic System of the brain controlling language of emotion and feeling tones as well as a somatosensory and emotional experience, and implicit memory. Finally, the Neo-mammalian complex is essentially the Neocortex controlling the language of thought and verbal expression, as well as intellectual and executive functioning, verbal language, conscious thought, and self-awareness. These are referred to as three independently conscious, “interconnected biological computers”, each with “its own special intelligence, its own subjectivity, its own sense of time and space, its own memory, motor, or other functions.”
Another primary topic of the book is the metaphor of Eden. Sagan views Eden as the time before human ancestors developed much of human cognitive abilities. Sagan says there are many biological reminders of a “pre-Eden” time, such as snakes, komodo dragons, and crocodiles which remain of the “dragons” that roamed in “pre-Eden” times. The evolutionary purpose of sleep and dreams, language abilities across species, and the purpose of mankind's innate fears and myths are also remnants of this time. Sagan views the biblical concept of mankind leaving Eden as a metaphor for the Dawn of Consciousness, approximately three million years ago. This is when mankind began to develop subtle, neocortical feelings, and became aware of things such as the difference between night and day. Humans left the dangerous Garden because of this loss of naivete and sought safety elsewhere. Animals developed a need for sleep as a result of becoming aware of the difference between night and day. During dark hours it was safer for early mammals to be still, and thus their bodies developed a need for sleep. This is also one of the driving factors for why humans sleep at night. Dreams evolved as a way to warn of danger during sleep. Dreams allowed our exterior environment to still influence our subconsciousness. Dreams also became a way of processing the new amounts of sensory input acquired during the day. From all of this came mankind’s language, fears, and myths--all of which stand to separate our intelligence from that of other animals.
In order to separate human intelligence from that of animals, one of Sagan’s main focuses was measuring intelligence. According to Sagan, the most important measure of intelligence is the ratio of brain to body mass, as opposed to the overall mass of the brain. In Dragons of Eden, Sagan has a diagram of brain versus body mass for various animals including primates, mammals, birds, fish, reptiles, and dinosaurs, with Homo sapiens ranking number one while dolphins rank second. Sagan believes that this favorable ratio causes the human brain to function the best and thus may be one of the reasons humans have been able to survive and rise to the top of the food chain. Human brains provide the ability to predict and reason about the future and consider the long-term benefits of actions, conscious and subconsciously. This gift comes with a price, such as anxiety and awareness of the inevitability of death. As well, humans are the only species known to experience pain during childbirth as a result of the large skull of human babies.
Animals with similarly favorable ratios such as apes, dolphins, and whales have evolved differently and share similar brain functions. They share human concerns with values, memory, subtle feelings, and communications. Dolphins talk to each other through variable clicks, too fast for the human ear to follow. Other high-level mammals show astonishing mental abilities as well. At the Yerkes labs in Georgia, Lucy, Washoe, and other apes have been taught hundreds of words via sign language, which were then programmed into a computer, and operated by the apes. Much like children in classrooms experimenting with computers, the apes learned to construct sentences like “Please give piece of banana” and then to make up sentences like “Baby in my drink” to indicate a small dot placed in Washoe’s drinking cup. Hence the Yerkish language; developed for the simian mind.
Similar intelligence in other species begs the question of why are humans the only species with human intelligence. Sagan goes into this by discussing the rituals performed by monkeys for dominance in the troop. Sagan’s discussion states, “The part that is involved is in the oldest part of the forebrain, a part that humans, as well as primates, share with our mammalian and reptilian ancestors.” It is every animal’s primal instinct to survive, and in doing so dominate. As a result, Sagan says humankind has systematically destroyed potentially intelligent, non-human organisms as a result of a primal, competitive urge. Sagan also speculates about the future of intelligence and believes it is possible that we may eventually need to consider other species, specifically primates, as similarly intelligent. He also considers the possibility of a similar or more intelligent extraterrestrial life.
While I personally found Dragons of Eden utterly captivating, I feel there should be a particular emphasis on the word “Speculations” in the title. As the book was originally published in 1977, many of the theories outlined have become outdated. For example, the concept of the triune brain. While the triune brain model may provide a clear relationship between brain structure and the evolutionary function of the human brain, various regions of the brain are involved in the activities each section is allegedly responsible for, as outlined above, there is not a neat division between primal, emotional, and rational activities in the brain. We have since learned that brain activity is far more spread out through the brain than what was believed in 1977.
The book can also be criticized for its controversial nature. The most controversial element likely is the aspect of religion in the book and Sagan’s analysis of the Garden of Eden. The book of Genesis has many different interpretations with no consensus of opinion. This is another reason why when reading Dragons of Eden, one must keep in mind the word “Speculations.” The concept of Eden and a dragon-filled “pre-Eden” world comes from Sagan’s own analysis of the book of Genesis with reference to his research. Personally, I find it interesting how Sagan synthesized religious concepts with his speculations on evolution. Sagan seamlessly crossreferences religion and scientific theory.
I believe that one must not read this book as a definitive science, but as the title suggests, as a series of speculations on the evolution of human intelligence. This book is a prime example of Sagan’s unmirrored ability to draw lines between science and other intellectual concerns such as myth, religion, and history, thus stimulating thought in the process. Sagan’s poetic writing style has led to a book of fluid readability and the capacity to convey and stimulate deep thoughts. The text sheds early light on cognitive science by calling forth elements of neuroscience, philosophy, computer science, linguistics, and anthropology. While this book covers complex topics, it is as much fun to read as a work of fiction.
The central theme of Dragons of Eden: Speculations on the Evolution of Human Intelligence is the idea that what separates the human species is our ability to harness the division in our minds. We harness the impulses and subconscious of our reptilian ancestors. We are capable of dreaming wildly, harnessing the power of imagination, and still applying logic and reason to our thoughts. The book itself reflects this ability. Sagan combines philosophy and introspection with religion and the reasoning of scientifically based speculation. It ends with the idea that the survival of our species is dependent on education and technology. The same technologies which may threaten our survival can also be harnessed to help and educate our youth. While Artificial Intelligence is experiencing a boom in the modern age, Sagan in 1977 was able to show a clear understanding of the ways Artificial Intelligence could someday aid us in many things, such as the search for life beyond our pale blue dot of a planet in the great landscape of the cosmos.
