Ideas & Trends: The Story of Us; The Other Secrets of the Genome
BIOLOGISTS have taken their first look at the human genome and report that its 30,000 genes, though fewer than expected, will help decipher the genetic basis of many diseases and in time revolutionize medicine. But what will the genome tell us about human nature?
There the predictions become far less explicit, as if the genome were going to tell us everything about our bodies and nothing about our behavior.
Dr. J. Craig Venter, president of Celera Genomics, concludes his article about the human genome with a warning against what he sees as the dangers of determinism, ''the idea that all characteristics of the person are 'hard-wired' by the genome.'' Dr. Francis Collins, leader of the public consortium that sequenced the genome and Celera's rival, said last week that ''one of the greatest risks of this focus on the genome'' is that people will draw the conclusion that their choices in life are ''hard-wired into our DNA and free will goes out the window and we move into this mindset of genetic determinism.''
It's easy to refute the advocates of genetic determinism, if any non-straw ones exist, because it is obvious to scientists that human behavior is not completely specified by the genome. But the opposite position -- that evolution does not care about and has in no way shaped human behavior -- seems equally implausible. Evolution is likely to have molded any and all behaviors that conferred survival value.
That may be easy to accept for behaviors like fighting and mating. But what about sophisticated human behaviors like art and religion? Art might seem a pure expression of human volition. But listen to paleo anthropologists debating the first appearance of art in the archaeological record and it seems that art, or some aspect of mind closely related to it, played a critical role in human evolution.
Most human societies have religious beliefs of one kind or another. Some may take that as proof of a universal creator. But for the biologist, the only question is whether such behavior is adaptive, meaning selected and genetically encoded because it conferred some survival value on the societies that possessed it. Religion is a source of spiritual values but has also served throughout history as a strong cohesive force among rival societies at each other's throats. Don't the bishops always bless the cannon?
THE human mind,'' writes the biologist Edward O. Wilson in his recent book ''Consilience,'' ''evolved to believe in the gods. It did not evolve to believe in biology. Acceptance of the supernatural conveyed a great advantage throughout prehistory, when the brain was evolving. Thus it is in sharp contrast to biology, which was developed as product of the modern age and is not underwritten by genetic algorithms.''
If a wide spectrum of human behavior from art to ethics is indeed adaptive, as biologists like Dr. Wilson believe may be the case, then the genome encodes a wealth of information about the essence of human nature. And that would transform it from a benign medical textbook into a document deeply disquieting to those who would prefer to believe the higher forms of human behavior and experience are transcendental states beyond the reach of mere genes.
Is it just human behavior that's exempt from evolution's shaping hand? Imagine the conversation among a group of fruitflies, whose genome was decoded last March:
''They'll never understand the Drosophilan nature from our genome -- there's so much more to us than mere genes.''
''Yes, the delirious high of being a wild young maggot, perpetually drunk while chewing through fermented fruit.''
''And how could mere genes determine the thrill of the courtship as I sing to my inamorata by vibrating my wings, and she listens to my song and accepts me.''
''Or rejects you with a buzz of her wings.''
BUT dear Drosophilans, the alcohol dehydrogenase enzyme that lets you survive in alcohol is one of the best studied proteins in biology. And your courtship behavior, sophisticated as it may be, is tightly controlled by two genes that biologists call ''fruitless'' and ''dissatisfaction.'' With a small change in the DNA of the fruitless gene, the males will produce an abnormal scent, court both males and females and fail to mate. With a different mutation, the males court only males and fail to sing their courtship song. Females with mutations in dissatisfaction resist mating by kicking wooers and flicking their wings to dislodge the suitors trying to mount them. How single genes can produce such surprising transformations is not yet fully understood, but it seems that the state of the fruitless and dissatisfaction genes pretty much specifies all the rules in the playbook of fruitfly dating.
With the human genome in hand, the way is open, at least in principle, to discover how it shapes the architecture of the human mind. ''Nearly all human behaviors that have been studied show moderate to high heritability,'' write Dr. Robert Plomin and colleagues at the London Institute of Psychiatry in a commentary in the current issue of Science. They believe that, in time, ''the human genome sequence will revolutionize psychology and psychiatry.''
Dr. Plomin, who discovered the first gene that affects human intelligence, describes the influence of genes on human behavior as ''probabilistic rather than deterministic.'' Dr. Wilson also expects that evolution has found it more effective to set loose prescriptions -- epigenetic rules, he calls them -- to guide those trying to survive in complex and hazardous jungle of human society.
All branches of human knowledge, he argues, from ethics to economics and aesthetics, will eventually be unified by understanding the genetic rules of the human mind. ''The search for human nature,'' he writes, ''can be viewed as the archaeology of the epigenetic rules.''So never fear -- the human genome is nothing like the bland medical textbook that those who decoded it are intent on describing. When fully translated, it will prove the ultimate thriller -- the indisputable guide to the graces and horrors of human nature, the creations and cruelties of the human mind, the unbearable light and darkness of being.