The Dragons of Eden-Chapter 2- Genes and Brains

 

Introduction

Biological evolution accompanies a linear increase in complexity. Look around you, it doesn’t take much time for us to realize that our world is quite complicated. The Earth hosts a variety of taxa (species, subspecies, and races), with the major taxa, which have evolved most recently, being the most complex. Humans, or homo sapiens, are in this bracket.

It is easy for us to identify, on the basis of our physical and mental attributes, functions and behaviors, factors that may set us apart from others, and contribute to our unique identity. By doing so, we have merely partaken in a significant evolutionary behavior, namely the ability to identify differences among ourselves, as opposed to other species, including members of our own taxa. Most often, we relegate our comparisons to distinctions based on the quantity, and quality of characteristics.

In this chapter, Sagan uses this notion as a medium towards the deeper understanding of our evolutionary history as a species by addressing the history of life in the gradual dominance of brains over genes.

The Book of Life

While a primitive notion on the complexity of an organism can be obtained by considering its behavior, and functions, we can do the same by considering the minimum amount of information contained within said organism. In other words, how much genetic material does the organism hold?

The book of life is written in the language of four alphabets, consisting of complex molecular structures called the nucleotides. DNA (Figure 1), or Deoxyribonucleic acid, the primary hereditary molecule, consists of about five billion pairs of nucleotides. In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes.

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Figure 1. The four alphabets of DNA, the nucleotides: Thymine, Adenine, Guanine, and Cytosine.

All the organisms on Earth share this genetic language composed of four alphabets, leading to the theory that we are all descended from a single ancestor, or a single instance of life some billion years ago.

“If there are approximately six letters in an average word, the information content of a human chromosome corresponds to five hundred million words. If there are about three hundred words on an ordinary page of printed type, this corresponds to about two million pages. If a typical book contains five hundred such pages, the information content of a single chromosome corresponds to four thousand volumes.” – Carl Sagan, The Dragons of Eden

Brains vs. Genes

The gradual dominance of brains over genes, the premise of this chapter, is shown to follow a practical necessity in the evolution, and survival of various species. The main working materials of evolution are mutations (Figure 2), heritable changes in the nucleotide sequences of our DNA.

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Figure 2. Well, not exactly…but you get the point. 

Most mutations/genetic changes are too slow for any practical benefit (occurring over millions of years). Most mutations are also harmful, and in some cases recessive. In the end, what really counts are mutations in the gametes, the eggs and sperm cells, the agents of sexual reproduction.

“Large organisms such as human beings average about one mutation per ten gametes-that is, there is a 10 percent chance that any given sperm or egg cell produced will have a new and inheritable change in the genetic instructions that determine the makeup of the next generation.” –  Carl Sagan, The Dragons of Eden

With such a high mutation rate to already cope with, a greater complement of DNA could suggestively result in unacceptably high mutation rates. Too much would go wrong, for anything to stay right! As Sagan postulates, there must be a practical upper limit to the amount of genetic information that the DNA of larger organisms can accommodate, thus by the same instance, necessitating the existence of substantial resources of extragenetic information to allow for their survival, and growth. Such information is contained in all “higher” organisms, except humans (who have invented extrasomatic knowledge, or information stored outside our bodies, like writing), exclusively in the brain.

Peering Into The Brain

The remainder of the chapter an exclusive tour de force of the brain. The corresponding questions, and their central arguments can be summarized as follows,

What is the information content of the brain?

There are two extreme opinions on brain function:

(a) The brain or the cerebral cortex (its outer layers) are considered to be equipotent; there is no localization of function, such that any part of the brain can substitute for another.

(b) The brain is completely hard-wired, and specific cognitive functions are localized in specific parts of the brain.

The actual answer lies somewhere between the two as has been portrayed by various experiments over the years. Modern-day neuroscience continues to address this question.

Is there a correlation between brain mass, and intelligence?

There isn’t a one-to-one between brain mass or size and intelligence in human beings, but there remains a statistical correlation nonetheless (namely in that there are upper and lower limits which may correspond to normal adult human brain function). It has been found that the correlation between brain size, and intelligence is much better than the correlation between intelligence, and adult body weight. Sagan presents the criterion of brain mass to body mass, with no consideration of behavior to provide an acceptable first approximation for intelligence.

What is the structure of the brain, or how is it packed?

The human brain contains about ten billion switching elements called neurons. There is contention among neurobiologists that neurons are the active elements in the brain, as evidence has been provided that specific memories and other cognitive functions are contained in certain molecules in the brain, like RNA or small proteins. An average neuron in a human brain is said to have been 1000-10,000 synapses. If we were to consider each synapse as equivalent to a on-off state, then the number of different states of a human brain is far greater than the total number of elementary particles in the entire universe. We are all truly unique!

The brain is basically a system of microcircuits, and a very dense on at that with an information content of ten billion bits per cubic centimeter. As Sagan points out, a modern computer able to process the information in the human brain would have to be about ten thousand times larger in volume than the human brain. Though the processing speed of a computer is far higher than the brain, the fact that our brain can do so many significant tasks so much better than the best computer is a testament to how tightly packed, and well-organized it is. We have yet to break this mystery, and come to a complete understanding of the brain, and its functions.

The End Game

Thus, having considered the quality and quantity of genetic material, and brain information in organisms, Sagan is able to compare the gradual increase through evolutionary time of both the genetic, and brain information of organisms, showing that somewhere around the Carboniferous period, a few hundred million years ago, there first emerged an organism with more information in its brain than in its genes. While Sagan refers this organism to be an early reptile, conflicting theories exist today in contention of this statement, and our earliest ancestor.

In conclusion, the evolution of the brain is a symbolic event in the history of life. The consequent bursts of brain evolution would result in the emergence of mammals, and of manlike primates. Nevertheless, there still remains much to the story.

“Mankind is poised midway between the gods and the beasts.”- Plotinus

As we will see in the following chapters, humankind’s naivety rests in its pride as the summit of the biological cycle, but while our authority on this Earth may be justified by the repeated insistence of our higher intelligence, and brain function, we are yet to realize that we are not so completely removed from the “beasts” themselves.

“…with all these exalted powers- Man still bears in his bodily frame the indelible stamp of his lowly origin.” – Charles Darwin, The Descent of Man

Phrenology1

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The Dragons of Eden – Chapter 1 – The Cosmic Calendar

“What seest thou else in the dark backward and abysm of time?” – William Shakespeare

Time is a component quantity of our daily lives. It is symbolic of the indefinite progress of existence, and events that are generally considered to occur in an apparently irreversible sequence from the past, to the present, and onto the future.

The concept of time has been central to the growth, and evolution of human civilizations. It has also served as an important facet of knowledge that has been studied to a great effect in religion, philosophy, and science. But, to this day, an absolute definition of time still evades scholars.

In The Dragons of Eden, Sagan does not extend his arguments toward an extensive discussion on the concept of time, but rather focuses on its use as a metaphor to describe humanity’s place in the cosmos. To infer the future, it is necessary for us to understand our origins. This is the basis of Sagan’s approach.

Now, it is argued that the predecessors of modern-day human beings, the Homo sapiens¸ evolved somewhere between 250,000, and 400,000 years ago. This number pales in comparison to the appearance of the first primitive humans, such as the Australopithecines, which happened somewhere between 8-9 million years ago. But, even these events, are preceded by an even greater “vista of time” reaching far back into the history of our planet, the solar system, and the universe. Very little is known about these periods of time, and even with the numbers mentioned earlier, we still struggle to grasp the immensity of these time intervals (Figure 1).

Figure 1. Humanity is yet to define its existence amidst the vast cosmos.

Nevertheless, science has found success in the establishment of specific methods that have allowed us to date events from the remote past, such as geological stratification (Figure 2), and radioactive dating (Figure 3).

Figure 2. Geological stratification, bluntly said, involves the study of rock layers, and layering.
Figure 3. Radioactive dating is a technique involving the tracing of radioactive materials in select objects, carbon dating is one such method that is limited to the dating of organic (carbon-based) organisms.

These two methods have provided information on archaeological, paleontological, and geological events. Astrophysical theory has provided for the same on a grander scale involving the dating of stars, planetary surfaces, galaxies, and the even the age of the universe (Sagan states this to be 15 billion years old, though recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) puts the number somewhere at 14 billion years old). The earliest event known in record is called the Big Bang, an intense explosion from the universe is said to have formed, but rather than a beginning, the Big Bang is generally considered to be a discontinuity in time where the earlier history of the universe was destroyed.

To put this further into perspective, Sagan introduces the Cosmic Calendar, where he compresses the 14-billion-year-old chronology of the universe, into the span of a single earth year. In this manner, one billion years of Earth history is the equivalent of twenty-four days of our cosmic year, and one second of the cosmic year is the same as 475 real revolutions of the Earth about the sun. The Cosmic Calendar is a humbling account of humanity’s place in the universe, with all our recorded history occupying the last few seconds of December 31.

Though a short chapter, Sagan’s use of the Cosmic Calendar is quite analogous to a common argument used in astronomy to provide a picture of our place in the universe (Figure 4).

 

Figure 4. Our place in the universe. The planet Earth is smaller than a speck among the greater part of the observable universe.

While the major premise of Sagan’s book focuses on discussions on the evolution of human intelligence, this introductory chapter is a necessary prelude that helps to symbolize the significance of the subject matter. While it may be true that humanity occupies an insignificant instance in the face of cosmic time, we are now embarking on a new cosmic year, one which is highly dependent on our ability as a species to come together, use our wisdom, and unique sensitivity to the world for our survival, and a greater future.

References 

The Dragons of Eden – Introduction

Mankind is poised midway between the gods and the beasts. – Plotinus

Plotinus’ quote is symbolic of a fundamental biological principle illustrating that man is descended from some lowly organized form, and which serves as the backdrop to the discussions Carl Sagan (Figure 1) presents in The Dragons of Eden. In order to provide a description of nature, and human growth, Sagan begins by discussing this principle, one that distinctly identifies the field from other physical sciences, evolution by natural selection.

Figure 1. Carl Sagan, noted astronomer, science communicator, and author of The Dragons of Eden.

Let’s digest that last bit, piece by piece. The word evolution is commonly used to describe the gradual development of something, from a simple to a more complex form. In scientific terms, evolution is the change evidenced in hereditary characteristics that are carried over successive generations in biological populations. It is the fundamental process that has led to biodiversity within species, and individual organisms.

Figure 2. Charles Darwin

Natural selection was the brilliant discovery of Charles Darwin and Alfred Russell Wallace (Figures 2-3), detailed in the publication of their joint works in 1858. It is the theory that describes evolution, and is the preferential survival and reproduction of organisms that are by accident better adapted to the environment.

Figure 3. Alfred Russell Wallace

Natural selection is due to differences in the phenotypes of individual organisms. A phenotype is basically a composite description of an organism’s traits and characteristics including its physical and biochemical properties, as well as morphology, development, and behavior. An organism’s phenotype is a consequence of an organism’s genetic code, or genotype, along with environmental factors, and the collective influence and interaction of the two. It is important to differentiate natural selection from artificial selection, or selective breeding, where humans use animal and plant breeding to “select” for the development of particular characteristics by choosing which males and females of animal and plant species will sexually reproduce, and have offspring together.

In The Dragons of Eden, Sagan, much like Jacob Bronowski (Figure 4), best remembered as the presenter and writer of the 1973 BBC television documentary series, The Ascent of Man, wants to provide an account of how human beings and human brains “evolved” or grew up together. By understanding the evolution of human beings and human brains, Sagan intends to provide a platform from which he can speculate on the nature of human intelligence, its evolution, and its future.

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Figure 4. Jacob Bronowski was a British mathematician, historian of science, theatre author, poet and inventor.

For starters, he addresses the role of knowledge and learning in a species’ ability to survive, and adapt to its environment. In order for an organism to survive, it must have the basic ability to extract and manipulate information from the environment. Most organisms depend on their genetic information to survive, but in their lifetime, they can also collect extragenetic information. On the other hand, humans and mammals exclusively depend on extragenetic information.

Mammals are warm-blooded (maintaining a constant body temperature compared to the temperature of the environment), vertebrate (have a backbone or spinal column) animals distinguished from other animal classes by their possession of hair or fur, the birth of live young, and the secretion of milk by the females for the nourishment of the young.

While our genetic history does exert a significant influence in our behavior, our brains allow for us to interact at a higher level with what we learn from the environment. This has drastically enhanced the chances of survival of the human species. Human beings have also invented extrasomatic knowledge, or information that can be stored outside our bodies, writing being a notable example. As Sagan points out, our dependence on extragenetic, and extrasomatic information is crucial to the survival of our species. Since the timescales involving evolutionary or genetic change is far too long, we cannot depend on a process that may take place over hundred thousands to millions of years in order to keep up with the changes that we encounter in the world. In fact, we now live in a time where our world is changing at an unprecedented rate. To deal with an unknown and perilous future, Sagan insists it will be necessary for humans to actively consider the changes in our environment, and learn to adapt, control, and adjust our lifestyles accordingly. Our survival relies on the evolution, growth, and sensitivity of human intelligence, which has been a solution and a cause to the many problems and changes that afflict our species (Figure 5).

Figure 5. Our evolution is tied to the growth of our environment, and vice versa.

Sagan’s interests in addressing the evolution of human intelligence is also an extension of the work he accomplished at SETI (Search for Extraterrestrial Intelligence) as the insights we derive from an investigation of terrestrial intelligence will help in our search for extraterrestrial intelligence.

Both the existence of those other civilizations and the nature of the messages they may be sending depend on the universality of the process of evolution of intelligence that has occurred on Earth. – Carl Sagan, The Dragons of Eden

Ultimately, his treatment of the evolution of the brain will assume that its workings, or what can be called the mind, are a result of its physiology and anatomy. His primary goal in addressing the evolution of human intelligence  is to dissect the various aspects of a subject that touches base with various other scientific fields. By understanding the evolution of human intelligence, he stresses the insight that can be gained from the interactions between brain physiology, anatomy, and human introspection.

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Figure 6. René Descartes, addressed the mind-body problem in the 17th century. He believed that inputs from the environment were passed on by the sensory organs to the brain and from there to the immaterial spirit

With this approach, Sagan considers the “mind” to be the result of collective processes of the components of the brain, and chooses to not entertain the hypothesis of what is called the mind-body dualism (Figure 6). The mind-body problem deals with various arguments about how mental states, events, and processes can be related to physical states, and likewise, with the governing assumption that the human body is a physical entity, while the mind is non-physical. (The Stanford Enyclopedia of Philosophy is a wonderful primer’s read-through of this highly detailed topic.)

And that’s all there is to the introduction! While it may read as a book review, the introduction is a concise summary of what we will see later in the book. Now, to reiterate, Sagan’s work in The Dragons of Eden  is presented against the backdrop of the theory of evolution. Since its induction in science, evolution has garnered its share of controversy, and disagreement. To all my readers, by reviewing this book, I am in no way forcing these views, and arguments on you. Science is not dogmatic, neither should it be in its endeavor to discover the nature of our world, and our place in it. It is an open stage, and thus, I leave it to you, my readers,to decide on the views you wish to accept, and decline in my review of the book.

References