Like many other great discoveries, Monday's release of the entire human genome sequence left scientists asking at least as many questions as finding answers. If, as the data show, we have only three times as many genes as a fruit fly and probably only a few hundred more than a mouse, what's the big deal about being human?
That's the kind of question that's perplexed me for years. It's what originally drew me to Fyodor Dostoyevsky's classic tale of passion and patricide -- the book jacket claimed that "all life is in 'The Brothers Karamazov.' " And it was a determination to find out what makes us tick that turned me into an evolutionary biologist.
You can see the attraction. To a young man with intellectual pretensions, the possibility of discovering the important truths about the human condition in two (admittedly hefty) volumes, and all for less than $10, seemed like a good investment. Today, anyone with a PC and a modem can double-click on the 21st century's "book of l! ife" -- as scientists have taken to calling the human genome -- and find within its pages the complete instructions for making homo sapiens.
But surely the most humbling feature of the human genome is how unremarkable -- compared to other genomes -- it is. Most of us would like to believe that humanity adds up to far more than three flies or one-and-a-bit mice, but there doesn't appear to be any evidence for this in our C's, A's, T's and G's. It seems likely that when the chimpanzee genome is complete, our uniqueness will be even more severely compromised. Those few human genes that are novel appear to be remarkable in neither their structure nor their likely function.
So where, I find myself asking, are we likely to find the distinctively human bits of us -- the stuff that, in its highest expression, allowed Dostoyevsky to write "The Brothers Karamazov" or Mark Rothko to paint the Seagram Murals? The answer, I believe, will be found not in the genes themselves, but in the! historic emergence of an entirely novel dynamic involving one product of those genes -- our brain -- and our environment.
Over the past decade, geneticists have claimed to find genes for human traits such as intelligence, aggression, criminality, homosexuality or even bad luck. Although many of these claims have been contradicted by subsequent studies, sociobiologists continue to assert that most of human behavior can be explained by evolutionary pressures on genes. You can find that argument any week in the scientific literature. Take the article "Toward Behavioral Genomics" in last week's issue of Science magazine -- but note that the authors give few clues as to where to look for the relevant genes.
If the relatively limited repertoire (compared to man's) of mousy activities is encoded by nearly as many genes as we find in our own chromosomes, there has to be some other explanation for the multitude of unmousy and peculiarly human activities in which we all like to ind! ulge. Such as our ability to appreciate art. To add two and two. To make cappuccino. And to send valentines.
Quite simply, we must be more than the sum of our genes. This conclusion is inescapable once we realize that the human genome has only been distinctly human for about 10 million of the 3 billion years that it has been evolving. Approximately 10 percent of our genes -- those that encode the basic building blocks of life -- are very ancient and are shared with nearly every animal on the planet. Many more are shared with vertebrates, and most are shared with mammals such as the mouse. Research already shows that about 99 percent of our DNA is identical to that of our closest cousin, the chimpanzee.
In fact, at the level of genes, there are far more differences between chimpanzees and monkeys than there are between chimps and us. (At the level of behavior, of course, quite the reverse is true.) If the human genome project had instead sequenced the chimpanzee genome, the! results would have been nearly the same. Nearly all of our genes were in place before we diverged from our primate cousins and climbed down from the trees. For the most part, they encode a great ape.
Something remarkable clearly happened after our ancestors separated from the great apes those 10 million years ago. It cannot have been any kind of "genetic revolution," because it has not left any significant imprint on our genome. Instead, the emergence of man must have been precipitated by a unique interaction between the product of our genes -- our body -- and the Paleolithic environment in which we then lived. It certainly involved our brain, since it is in this structure that we see the greatestphysical difference between our cousins and ourselves. But it is not just a matter of increasing size. The brain of a pygmy marmoset is not much bigger than a chestnut, yet the tiny South American monkey shares most of the complex behavioral patterns of a chimpanzee, with its much! larger brain. In man, something entirely novel evolved: the human mind. That event seems to have coincided with the flowering of the most extraordinary product of our brain -- human consciousness -- and it is hard to escape the conclusion that the two events are causally linked. Nearly all uniquely human endeavors -- creativity, love, spirituality and problem solving -- are impossible without conscious decision making. Consciousness -- or self-awareness -- is what makes us human. Take away our conscious mind and we are left with animal instincts: lust, hunger, anger or fear. Man without consciousness is a monkey.
If consciousness, as a dominant stimulant of human behavior, arrived late in our evolution and didn't involve any major genetic changes, what caused it? How does it work? These are, of course, huge, much-debated questions. My own suspicion is that consciousness arose as a side effect -- almost an accident -- of the evolutionary drive to pack more and more neuron! s into our cranium. An entirely novel route toward information processing was laid down in our overcrowded skulls, and the dynamics of that pathway have formed our conscious mind.
Whatever the mechanism, there can be little question that our minds are generated not by our genes in isolation, but by a complex interaction between our genes and our environment. In a sense, our genes provide the framework and our environment -- our parents, friends and experiences -- create the solid structure.
With that in mind, you can see that looking for genes that encode the mind is like looking in the strings of a piano for Chopin's nocturnes. Sure, the strings are important. If any are out of tune, then you will get an awful racket. Similarly, if any of our genes are out of tune, all sorts of psychological and behavioral problems might ensue. But that doesn't mean that genes make minds any more than piano strings make sonatas.
I don't mean to diminish the utility of the human genome p! roject. Though we are still a long way from understanding how these long strings of A's, T's, C's and G's are turned into a living, breathing person, the genome map will be a fantastically valuable resource for science and medicine. The 3 billion digits of genetic information surely have treatments and cures for hundreds of diseases -- from cancer to heart disease or even old age -- lurking within the code.
But the genome does not provide the complete picture. One of its most striking features is how it seems to have been cobbled together from bits and pieces of whatever was lying on the cutting room floor of evolution. More than 200 of our genes appear to have been captured from bacteria, and much of the rest of our genome is a junkyard filled with the corpses of virus and other parasites that have been hopping in and out of our chromosomes for millennia. So much for the extremist ideal of racial purity: Mankind cannot even claim to have maintained species purity.
Another remarkable finding is the seemingly higgledy-piggledy way our genome has been put together. By comparing our chromosomes to those of other species, we can see that in addition to inserting new genes, nature has rearranged, duplicated and deleted large segments of our chromosomes, on average performing one genetic shuffle every million years. Charles Darwin, commenting on his theory of evolution in "The Origin of Species," claimed that there was "grandeur in this view of life." Biologists may be surprised at how haphazard that grandeur now seems to be. Nature has in fact been busily chopping and changing our genes for millennia -- a sort of natural form of genetic engineering.
At the endpoint of 3 billion years of evolution, the genome's discovery is undoubtedly one of mankind's greatest achievements.
But the genome does not explain man.
What makes us unique as individuals does not lie in our genes. (My genes differ from yours in only about one in every thousand genetic ! digits.) It lies in the richness of the environment that makes each of our minds. The human genome will revolutionize our understanding of our biology. But it will not tell us what it means to be human. For the time being, in searching for the answer to that riddle, I would still put my faith in Dostoyevsky.
Johnjoe McFadden