Genes Are Like Sentences, Genomes Are Like Books

I lose track sometimes of exactly what the common genetic terms mean and how the genetic pieces work together. What’s the difference between a chromosome and a strand of DNA? A gene and a genome? What are those three-letter sets in a DNA diagram called and what do they do? I’m not a scientist, but since I was an English teacher, connecting the names of genetic units to the units of written language—words, sentences, and so on—makes the picture a little clearer.  Maybe it will do the same for the reader.

Let’s start small.  The spiraling rungs on diagrams of a DNA (deoxyribonucleic acid) molecule are each marked with two of four specific letters: A, C, G, and T.  The four DNA letters stand for the four nucleotides—Adenine, Cytosine, Guanine, and Thymine—that make up DNA. Like the letters of the full alphabet, these letters–or rather the four molecules they indicate–are the smallest building blocks of their language.

codons

moodle.clsd.k12.pa.us

In DNA, combinations of the letters for the four nucleotides make up the three-letter codons that are DNA’s version of words. Each three-letter codon/word specifies one amino acid. And most codons are “synonyms” in that several different codons refer to the same amino acid because there are many more codons than there are amino acids. The codons are “read” by a ribosome, a cellular reader/assembly-machine that produces the required amino acid and attaches it to the chain of amino acids that will form a protein.

Groups of these codons make up a gene, much as words make up a sentence. The genes/sentences are long because most proteins are complex; human proteins consist of anywhere from several hundred to several thousand amino acid molecules.  The gene/sentence for red hair says something like “Put this together with that and that and that….”

Genes also include a codon at the start that says “Start the gene here” and another at the end that says “Stop here; gene complete.” Within the gene, however, no actual spaces separate the codons, but since all codons are triplets, it’s always clear where codons themselves begin and end.  (Somewhat similarly, writing in the ancient world often lacked spaces between words.  As long as one could read slowly and figurethewordsoutspacesweren’tessential.)

chromosome (mayoclinic.org)

mayoclinic.org

So, to recap.  The four nucleotides are basic components much like the letters of our alphabet. Groups of three nucleotides spell out codons that can be thought of as words, which in this case are actual amino acid molecules.  And a sequence of codons/amino acids forms a gene that resembles a sentence in a protein recipe for some aspect of the organism.

Finally there are chromosomes and genomes.

A molecule of DNA is very long, a continuous strand of anywhere from a couple of hundred to more than a thousand genes, many of them about related aspects of the organism. Each molecule is a chromosome which, because its genes concern similar aspects of the body, can be compared to a chapter in a book.  But it is a strange book in that each chapter appears twice, in anticipation of the day when the molecule/chapter reproduces itself. Each human cell contain 23 such paired chromosomes, duplicate copies of the assembly instructions for an entire human being. Only the chromosome pair that determines sex contains chromosomes that are different from each other about half the time: females have two identical female chromosomes while males carry one female and one male chromosome.

Finally, our genome is like the book itself, the totality of all our genes on all our chromosomes. The book might be called Me And Us. Your genome book is almost exactly like mine except for about one tenth of one percent of our 20,000 genes that are different. That’s similar to two copies of the same long book that differ only in a few sentences.

Simplified though the comparison is, it’s startling what genetics and written language have in common considering that the second is a recent human invention and the first represents the formation of life almost four billion years ago. Both are composed of the smallest building blocks, then the groupings created from the building blocks, then the meaningful statements/instructions/recipes coded in the groupings, and finally the conversion of the code into organic construction/action/speech.

“There’s No Natural Selection For Happiness”

“Like evolution, history disregards the happiness of individual organisms” (243) writes Yuval Noah Harari in Sapiens: A Brief History of Humankind. Harari takes us through early human history to note its indifference to personal well-being and its drive toward population growth—two features that also mark the forward motion of evolution. It is only in the modern era, he believes, that civilization may be doing more for individual happiness, and the price we pay for that shift may be to leave nature further behind.

It’s a provocative view. Most people carry around a vague but positive sense of the progress of history. After all, I’m sitting here with my computer, with food and water in the kitchen, in a peaceful town. Many others are not so fortunate, but that’s the task for the future, not a sign we have misread the past, as Harari argues.

He looks at three revolutions. By 70,000 years ago, after the Cognitive Revolution, we Sapiens could talk and think as well as we do today. Ten thousand years ago, during the Agricultural Revolution, we began growing food instead of just gathering it. The last 500 years has been the Scientific Revolution.

In between the Cognitive Revolution and the Agricultural one, intelligent, food-gathering Sapiens led healthy, mobile, and interesting communal lives. Their diet was varied, work was not arduous. But when they took up growing a few crops, raising animals, and settling down, they left the mobile community behind in exchange for towns, cities, and elites. The food supply and the farmers themselves became susceptible to drought and disease, and labor became exhausting and monotonous. Agriculture produced larger populations but not happier ones. And it did so in small steps, as each new luxury—food storage, land ownership, cities—became a necessity that no one wanted to give up.

(islandbreath.blogspot.com)

(islandbreath.blogspot.com)

This process—small steps, no going backward, and a growing population—is also the footprint of  evolution. The right genetic change means a human who is a slightly better fit for the environment along with children who inherit the benefit. Happiness is not one of the steps, however. “There’s no natural selection for happiness” (386).

Since the Scientific Revolution 500 years ago, the ambivalence of cultural progress has deepened. Sapiens, Harari writes, have attained more control over nature while destroying a growing number of species. We have reduced extreme poverty and illness and raised global population numbers, but we’ve also raised expectations about a better life and in so doing have raised discontents as well. We may be progressing towards god-like abilities to prolong and even design life itself, yet we remain in the dark about what we want to become.

As we modify the human body more drastically through surgery and genetics, will we even remain human? The “Brief History” in Harari’s title refers not only to the book but also to a question about the duration of Sapiens as a species.

I found the first half of Sapiens, about the foraging era and the Agricultural Revolution, more convincing than the second part about the present. I’m skeptical that we Sapiens have ever been very good judges of the era we are living in or of what our future will look like. But warnings, disillusionments about our past, new angles of vision—all of which this book provides—are valuable and often fascinating.

I’ll conclude by letting Harari speak for himself, especially about language, the growing power of human “fictions,” social groups, and the foraging and agricultural cultures.

The new linguistic skills that modern Sapiens acquired about seventy millennia ago enabled them to gossip for hours on end. Reliable information about who could be trusted meant that small bands could expand into larger bands and Sapiens could develop tighter and more sophisticated types of cooperation…. Yet the truly unique feature of our language is not its ability to transmit information about men and lions. Rather, it’s the ability to transmit information about things that do not exist at all….Legends, myths, gods, and religions appeared for the first time with the Cognitive Revolution….Fiction has enabled us not merely to imagine things, but to do so collectively. We can weave common myths such as the biblical creation story, the Dreamtime myths of Aboriginal Australians, and the nationalist myths of modern states. Such myths give Sapiens the unprecedented ability to cooperate in large numbers. (21-25)

Sociological research has shown that the maximum ‘natural’ size of a group bonded by gossip is about 150 individuals….Below this threshold, communities, businesses, social networks and military units can maintain themselves based mainly on intimate acquaintance and rumour-mongering….But language enables us to create fictions, myths that could unite hundred of millions of people….Churches…States…Judicial systems are rooted in common myths….There are no gods in the universe, no nations, no money, no human rights, no laws and no justice outside the common imagination of human beings… [So-called “primitive” people] cement their social order by believing in ghosts and spirits. What we fail to appreciate is that our modern institutions function on exactly the same basis. Modern business-people and lawyers are, in fact, powerful sorcerers. (26-28)

Ever since the Cognitive Revolution, Sapiens have thus been living in a dual reality. On the one hand, the objective reality of rivers, trees and lions; and on the other hand, the imagined reality of gods, nations and corporations. As time went by, the imagined reality became ever more powerful, so that today the very survival of rivers, trees and lions depends on the grace of imagined entities such as the United States and Google. (32)

Sapiens did not forage only for food and materials. They foraged for knowledge as well. To survive, they needed a detailed mental map of their territory. To maximize the efficiency of their daily search for food, they required information about the growth patterns of each plant and the habits of each animal….Each individual had to understand how to make a stone knife, how to mend a torn cloak, how to lay a rabbit trap, and how to face avalanches, snakebites,or hungry lions….The human collective knows far more today than did the ancient bands. But at the individual level, ancient foragers were the most knowledgeable and skillful people in history. (48)

On the whole foragers seem to have enjoyed a more comfortable and rewarding lifestyle than most of the peasants, shepherds, labourers and office clerks who followed in their footsteps. …The forager economy provided most people with more interesting lives than agriculture or industry do….In most places at most times, foraging provided ideal nutrition… The foragers‘ secret of success , which protected them from starvation and malnutrition, was their varied diet. Farmers tend to eat a very limited and unbalanced diet….Ancient foragers also suffered less from infectious diseases. Most of the infectious diseases that have plagued agricultural and industrial societies (such as small pox, measles and tuberculosis) originated in domesticated animals and were transferred to humans only after the Agricultural Revolution….Average life expectancy was apparently just thirty or forty years, but this was due largely to the high incidence of child mortality. Children who made it through the perilous first years had a good chance of reaching the age of sixty, and some even made it to their eighties. (51)

[About 10,000 years ago,] Sapiens began devoting almost all their time and effort to manipulating the lives of a few animal and plant species. From sunrise to sunset humans sowed seeds, watered plants, plucked weeds from the group and led sheep to prime pastures.…  Scholars once proclaimed that the agricultural revolution was a great leap forward for humanity. They told a tale of progress fueled by human brain power. Evolution gradually produced ever more intelligent people. Eventually, people were so smart that they were able to decipher nature’s secrets, enabling them to tame sheep and cultivate wheat. As soon as this happened, they cheerfully abandoned the grueling, dangerous, and often Spartan life of hunter-gatherers, settling down to enjoy the pleasant, satiated life of farmers.

       That tale is a fantasy. There is no evidence that people became more intelligent with time. Foragers knew the secrets of nature long before the Agicultural Revolution, since their survival depended on an intimate knowledge of animals they hunted and the plants they gathered. Rather than heralding a new era of easy living, the Agricultural Revolution left farmers with lives generally more difficult and less satisfying than those of foragers. Hunter-gatherers spent their time in more stimulating and varied ways, and were less in danger of starvation and disease. The Agricultural Revolution certainly enlarged the sum total of food at the disposal of humankind, but the extra food did not translate into a better diet or more leisure….The Agricultural Revolution was history’s biggest fraud. (79)