Thousands of years ago, a tribe of Asiatic people speaking a strange tongue invaded the land that is modern-day Finland. This prehistoric event is visible within the uniqueness of the Finnish language. Yet linguistic analysis can never tell us how the invaders actually treated the indigenous people. Remarkably, this detail of the ancient invasion is revealed in the DNA of young Finnish boys alive today. The foreigners killed the local men and settled down to have babies with the local women.
On a Long Island playground this morning, a Jewish child carries a different message in her DNA. It is a message from the overcrowded Eastern European ghetto which her ancestors called home a few centuries ago. Her ancestors used this very same DNA message to stay alive as they watched their neighbors die.
Other mind-boggling messages from the past are hidden in all of us. You and I carry faint echoes of LUCA, the pugnacious little proto-life form that existed for a moment, four billion years ago, and spawned every living thing on the planet today.
Take a stroll down one of your own DNA molecules away from this unbelievably ancient message, and you will come to a spot bearing actual scars of a war that took place almost yesterday. The war was between your mother's genes and your father's genes. A truce was called, and you were born, but different battle scars on your maternal and paternal DNA are still there for you to see.
All of this may sound like the plot of a Stephen King novel, but as Matt Ridley explains, the reality of the "Genome" is much stranger than fiction.
To appreciate how ancestral messages can be written in our DNA, only a small amount of background understanding is required. The idea that living things contain hereditary information which is passed on to offspring is at least as old as human civilization. It was the essential knowledge required to begin domesticating plants and animals. However, the nature of the hereditary information remained a mystery until 1952, when James Watson and Francis Crick discovered the structure of DNA. Within this structure, the language of heredity was shown to be discrete and digital.
The hereditary information in each human being can now be viewed as a "book" containing about 3 billion characters of text written into molecules of DNA. This is no mere metaphor. The text of my genome is as real and discrete as the text of this book review (which, at the moment, exists only as a string of bits on a computer disk). Over the last two decades, scientists have created sophisticated machines that automatically "read" text from DNA and "write" it into computer memory. The Human Genome Project is a competitive public-private effort to read the whole book of 3 billion characters (the genome) and place them all in the right order. It will soon be completed. Actually, as Ridley points out, each human being carries a slightly different text. The first "human genome" to be posted as a file on the web (or sent out on a DVD disk) will be a random composite from many individuals.
That's all the science you need to know to appreciate Ridley's "Genome," which is unlike any other popular book on the topic of genes. This is not a book about the Human Genome Project or the way research is carried out. Ridley does touch upon the incredible potential of genetics for alleviating human misery, and he can't help releasing regular salvos at the anti-genetics crowd. But much of this remarkable book is focused on a higher plane of pure intellectual discovery. It is a nearly jargon-free expedition that hops from one human chromosome to the next (23 in all) in search of the most delightful stories. Even practicing geneticists -- apt to view the genome as a boring research tool -- will come away with a greater sense of wonder for the hidden secrets within the text.
The main theme of "Genome" is that your very own personal genome contains "echoes" (Ridley's evocative word) of the lives of your ancestors. Some echoes, like LUCA, have been around for billions of years and are shared by everyone. Others are much more recent and distinguish individual family histories. The Tay-Sachs mutation got passed down from ancestors who gained protection from tuberculosis, which was rampant in overcrowded urban areas. Similarly, the sickle cell mutation got passed down from ancestors who lived in tropical areas infested with malaria-bearing mosquitoes.
And how we do know that early Finnish invaders killed the local men and made babies with the local women? It's because all Finnish boys carry a distinct Y chromosome passed down from those invaders. The rest of their genomes are no different from other Europeans and were passed down from indigenous women living in Finland before the invasion. Ridley tells other message-in-the-DNA stories in "Genome" and leaves no doubt of a future in which many more come to light as more human genomes are read and interpreted in the context of historical knowledge. Perhaps there will come a day when graduate students in history are required to take courses in genetics.
In addition to genetic messages that once helped an ancestor (but typically serve no purpose for the bodies they inhabit today), there are huge tracts of the human genome that never helped anyone. These regions are teeming with genetic parasites which hitchhike onto your chromosomes and pass "themselves" into your children, without your knowledge. You'll be surprised at the portion of your genome occupied by this useless baggage: it's at least 95%. Just as amazing, the 5% actually required to bring you into existence is itself a battlefield of conflicts "between parental genes and childhood genes, or between male genes and female genes." As Ridley says, these ideas have shaken the philosophical foundations of biology, but they are little known outside a small group of evolutionary biologists.
From genomic secrets that have nothing to do with our daily lives, Ridley switches to the most contentious area of modern genetics: human behavior. He has nothing but contempt for those who would deny the role played by genes in personality, gender, and intellectual differences among individuals. He provides an example of psychologists who observe a child behaving like a parent and assume without question that environment must be the cause, although a child receives both environment and genes from his parents. As Ridley points out, ordinary people have always known that both genes and environment influence personality and ability. Only the experts have argued otherwise. But it's not simply that genes and environment get added together. Rather, each feeds back into the other, giving rise to a never-ending circle of cultural and genetic evolution.
Behavioral genetics is so contentious because, more than any other area of science, it has direct impact on both political theory and practice. Imagine what the world might look like if genes really did influence behavior and abilities. In a perfect meritocracy, where environments and opportunities are all equalized, genes would still be of utmost importance in determining who wins and loses. And in a court of law, a defendant's genes would have to be considered the same way that "mental status" is today in determining whether someone is fully responsible for his actions. (Of course, the same problem should arise with strong cultural influences on behavior as well.)
Such scenarios are far too frightening for some academics to consider, and thus, they reject a genetic influence on behavior without even taking the time to study the science or data. In contrast, Ridley believes that a quest for social justice must start with an accurate understanding of human biology.
In the final segment of his book, Ridley challenges the traditional academic analysis of the early 20th century American eugenics movement. The blame for this sorry chapter of history is often placed squarely on the shoulders of over-reaching geneticists. Not surprisingly, modern geneticists routinely denounce eugenics as bad science.
Ironically, the current state of science and technology is so advanced that eugenics is no longer scientifically implausible. If people with little understanding of heredity could turn wolfs into different breeds of dogs, our current state of knowledge could, in theory, be used to control the look and behavior of future generations but, as Ridley says, "at a gigantic cost in cruelty, injustice and oppression." What is wrong with eugenics is not the science but the coercion. It moves reproductive decisions away from the individual and into the hands of the state. Eugenic laws and practices were not an example of science out of control. They were an example of government out of control.
In the end analysis, Ridley is adamant in his belief that the knowledge and use of personal genetics cannot be left to physicians, ethicists, or governments to control. Instead, Ridley argues, individuals have a fundamental human right to see and use the messages in their own DNA as they see fit.
Lee M. Silver is a professor of molecular biology and public affairs at Princeton University and the author of "Remaking Eden: How Genetic Engineering and Cloning will Transform the American Family," published by Avon Books (1998).