A television show, Law and Order, opens each episode with a narrative line about the role of the police and prosecutors in the criminal justice system, which closes, "And these are their stories." Matt Ridley might have opened Genome by stating, "There are 23 chromosomes that make up the human genome, and each have special roles (plural) in determining or influencing our development, our physical attributes, our behavior, the kind of diseases we suffer or have immunity from, how long we might live, and when we might die. And these are their stories." Don't misunderstand me. Genome is not a complete encyclopedia of either genomics or the human genome. Just 23 interesting stories from one of the world's fine science writers, each story artfully tied to one of the 23 human chromosomes, from largest to smallest, covering topics such as life, species, history, fate, environment, intelligence, instinct, self-interest, sex, disease, stress, personality, development, life and death, memory, gene therapy, politics and ethics, eugenics, free will and determinism. The breadth of the subject-matter covered by this volume speaks to almost all of the topics covered by the books previously described in this blog, including a central theme: that units of information are the most fundamental units of life. (See September 28, 2010 post).
Ridley calls the genome a book, the chromosome a chapter, the gene a story, an exon a paragraph, a codon a word consisting of three letters, and a base is a letter, either (in the case of DNA) an A, C, G, or T (or U in the case of RNA), for adenine, cytosine, guanine, and thymine, each consisting of one or two aromatic rings and arrangements of carbon, hydrogen, nitrogen, and/or oxygen atoms. These chemical units are the basic units of information that comprise life forms, but alone they do not give rise to life. What gives rise to life is (1) the pairing of these letters along a double helix that makes up DNA, and (2) their subsequent transcription into RNA to form three letter codons, which, (3) are subsequently "translated" into a specific amino acid depending on which three of the four letters are transcribed and their sequence. (4) The particular chain of amino acids creates a protein. By this process, it is said that "genes" code for "proteins." While the RNA amino acid chains may have been the earliest form of life, "life" as we know it received a boost with the creation of cellular membranes to form the first cells that carried the proteins containing genetic information central for the cell's organization. This development is still not fully understood.
This ability of the genes to copy themselves, read and transmit their story, under the right conditions, is the ability to create another life form. My son once asked asked me, "What is Life?" a question posed in his high school biology class, and I replied that at its most fundamental level it is carbon-based, with a mechanism to replicate itself. The only two things I would add, consistent with the very first book discussed in this blog, Seth Lloyd's Programming the Universe (see August 17, 2009 post) is the ability of these units of information to communicate among themselves --- an electrochemical means --- to say "Let's stick together," or "Let's avoid each other," and then to store itself as if in memory. This is what we find in the genome, whatever the species.
This story never ceases to amaze me. Life began with RNA --- which by itself can replicate itself, and translate and transmit its meaning, as well as catalyze with --- break up or join with --- other chemicals, creating amino acids and proteins. The storage device for these words and paragraphs is DNA. An RNA gene found on chromosome 1 translates the information found in DNA to proteins, which become the primary agent for carrying out the direction specified by the information contained in the genes within a cell.
I cannot cover every "chapter" in Genome, but four topics that reappear throughout this blog --- so we can connect the dots --- are important in my mind: (1) is behavior found in our genes? (2) the role of our genes in our development after birth, (3) human memory and the mind; and (4) determinism vs. free will.
Is behavior found in our genes? This topic was first confronted in the post on Richard Powers' novel Generosity (November 30, 2009 post), Frans DeWaal's The Ape and The Sushi Master (June 17, 2010 post), and subsequently Oren Harman's The Price of Altruism (October 13, 2010 post). The answer then, as it is now, is no. There is no gene for spitting or laughing or speaking English or for believing in a god. What genes do code for enables or influences behavior, but they do not determine specific behavior. Just as it would be incorrect to say that behavior is entirely written in our genes, it would also be incorrect to state that behavior is entirely attributable to environment, including the nurturing, learning, social and cultural environments. Behavior is the outcome of the genome that defines us and the environment in which we develop and live.
Ridley notes the significance of instinct, something which was important to Darwin in The Origin of Species. Behavior that is instinctive to a species is arguably heavily enabled or influenced by genetic information. So we may refer to a language instinct, to borrow Steven Pinker's words, but a language instinct does not develop without some environmental influence. The genes that become proteins instruct the creation of the mouth, the tongue, and the air passages that enable human speech, and further instruct in the creation of the modules of the brain and the neuronal pathways between them that enable human speech and perhaps even language syntax. But at some point in the course of a life, learning takes over. The ability to learn --- social behavior --- is also something that is enabled or influenced by genetic information, but genes are not the end of the story.
The role of genes in development. This story was detailed in Sean Carroll's book Endless Forms Most Beautiful, which accounted for the role of the Hox and hedgehog genes in providing a program for both embyonic development and development after birth. These genes regulate cell division, the timing at which genes are switched on to control development, and determine such things as symmetry in the body of an animal, where arms, legs, antennae, fins, fingers and the like appear. Ridley retells this story on Chromosome 12. This is one of the most fascinating stories in evolutionary genetics as these are among the oldest of genes.
Memory. One of the more important subjects in the study of the brain is its plasticity, the brain's ability to change by removing, adding or strengthening neural connections. "When you learn something," Ridley notes, "you alter the physical network of your brain so as to create new, tight connections where there were none or weaker ones before." Connections between never cells "not only provide the mechanism of memory, but are memory." Ridley is not clear on how specific genes are tied to learning and memory, but he suggests that proteins connected with certain genes "are probably needed for holding the synapse closely together." We know more about the process by which memories are created and stored in the brain: sensory information is received in the perirhinal cortex found in the medial temporal lobe and sent to the hippocampus and to the diencephalon for temporary storage. If the information is significant enough for more permanent storage, it is sent back to the neo-cortex as long-term memory. Eric Kandel's research, documented in his memoir, In Search of Memory, traces the electro-chemical process in the brain by which connections between the neuronal connections at the synapses of neurons are strengthened.
Learning "is the opposite of instinct," Ridley says. "Instinct is genetically-determined behavior; learning is behavior modified by experience. . . .Human beings achieve by instinct the same things that animals do. We crawl, stand, walk, cry and blink in just as instinctive a way as a chick. We employ learning only for the extra things we have grafted on to the animal instincts: things like reading, driving, banking and shopping." Consciousness, Ridley quotes another, "is to enable [the child] to learn things which natural heredity fails to transmit." The brain is created by genes that designed the brain to be modified by experience.
Determinism vs free-will. The final chapter is almost whimsical --not truly a story about Chromosome 23, but an excuse to pontificate on whether free-will is possible given that a combination of genetics and the environment seems to determine everything about us. Free-will, in my view, if it exists, is enabled by the brain --- it is tied to the same type of issues that Ridley discusses in connection with learning and memory. Human behavior, says Ridley, is unpredictable in the short-term, but quite predictable in the long-term. As an example, he cites that at any given time during a day one can choose to eat or not to eat, but over the course of a day one will have to eat. When one eats is a function of genetic and external influences that makes behavior unpredictable, but not undetermined. "Freedom lies in expressing your own determinism:" being able to control voluntary movement in the gap between short-term when behavior is unpredictable and the long-term when it is predictably determined, It is in the brain of humans, and perhaps some other animals, that the ability to control voluntarily movement is found. And genes have enabled this ability in the design of the brain.