The Need for Cooperation Is in the Genes

By Gary Marcus

Los Angeles Times, Op-ed, January 4 2004

St. Francis is said to have called all creatures, no matter how small, brother and sister because he knew they had the same source as himself. Fifty years ago, science identified its version of that source: DNA, the double-stranded molecule of life. Apart from a few viruses, every creature, great and small, owes its very existence to the DNA molecule. Consequently, analysis of DNA promises to hold the key to unlocking how and why humans differ from other animals.

With the announcement in early December that the chimpanzee genome had been sequenced, it may seem like answers are at last just around the corner. It is not hard to imagine some cosmic version of the children's game "spot the difference," in which a simple inventory of the differences between the chimp genome and the human genome will tell us all we need to know about what makes humans special. But in reality, the two genomes, chimp and human, are simply long lists of "letters" (DNA nucleotides), and knowing how these letters differ doesn't tell us what those differences mean.

In some ways, scientists are more puzzled than ever; as recently as a few years ago, most assumed that the complexity of human nature would be mirrored in the complexity of the genome. Nobody anticipated that the human genome would have scarcely more genes than that of a chimpanzee, or that 80% of the genes in a mouse would have some counterpart in a human. It is now clear that radically different species can have startlingly similar DNA.

In hindsight, the great genomic similarities that are emerging should not be so surprising. Genes are, first and foremost, about building the ingredients of life, and all living organisms are made up of the same basic chemical elements and dependent on some of the same basic metabolic and cellular structures. To say that two creatures have similar genes is a bit like saying a bagel and a croissant have similar ingredients; the real trick is understanding how those ingredients are combined.

This much is already known: Whereas sugar and flour passively depend on a baker, genes take a far more active role in the body's self-assembly. Every gene contains both a template for building a particular protein (such as collagen or hemoglobin) and instructions for regulating when and where that protein will be built. And initial results suggest that it is in the latter, "regulatory" portion that the biggest differences among species lie.

Although the protein template portions of our gene sequences differ on average by less than 2% from those of chimpanzees, the regulatory regions may differ by as much as 12%. As we come to better understand how those all-important regulatory regions work, we will have an entirely new way in which to understand what makes humans unique, and how that uniqueness relates to the vast library of genetic material we share with other creatures.

But this is not a problem for genomics alone; the spectacular gene "sequencing" machines that identify DNA nucleotides by the billions are still just transliterators, devices that read letters. To fulfill the promise implied in the newly sequenced chimp genome, universities - and society at large - will need to increase support for something that they have long given lip service to: interdisciplinary research. For puzzling out what makes humans special is not just about spotting the differences but understanding what those differences mean.

To make the most of our growing knowledge of how genomes vary between species, biologists need the help of many others. To assess the influence of a given gene on the brain, for example, will require cooperation among neuroscientists who can assess how that gene influences the development and function of the brain, psychologists who can assess the influence on behavior, linguists who can speak to the question of language and anthropologists who can speak to the question of culture.

The sheer rate of research makes it impossible for any single scientist to know everything about his or her own field, so it is essential that society support the rare researchers who try to work beyond the boundaries of their own disciplines. Universities reward psychologists for being good psychologists and biologists for being good biologists but stint on supporting biologists who delve into psychology or psychologists who stray too far into biology.

It may take Congress to change that way of thinking, to shake up the staid ways of the academy, but in the end only an increased fostering of interdisciplinary research will allow us to truly understand what makes us uniquely human.

Gary Marcus, associate professor of psychology at New York University, is author of "The Birth of the Mind: How a Tiny Number of Genes Creates the Complexity of Human Thought" (Basic Books, January 2004).