Copyright The New York Times
The discovery of the structure of DNA in the early 1950s is one of the most riveting dramas in the history of science, crammed with brilliant research, naked ambition, intense rivalry and outright deception. There were many players, including Rosalind Franklin, a wizard of X-ray crystallography, and Francis Crick, a physicist in search of the secret of life. Now, with the death of the American geneticist James Watson at 97 on Thursday, the last of those players is gone. That wrenching drama ultimately changed how we conceived of life, and of ourselves. As the discovery of DNA recedes into history, it becomes difficult to even imagine how people thought about life before that breakthrough. In earlier centuries, natural philosophers would write about a mysterious “vital force” inside of cells that set life apart from inanimate matter. Physicians noticed hereditary afflictions carried down through the generations, but they had no idea of how that happened. “The laws governing inheritance are quite unknown,” Charles Darwin acknowledged in 1859 in “The Origin of Species.” Darwin went on to tackle that mystery and failed to solve it. He imagined that particles streamed from through the body into the sperm and eggs that gave rise to the next generation. Gregor Mendel, planting peas in his garden at about the same time, came closer to a solution. He discovered that his plants inherited colors and other traits in reliable ratios. But he could only speculate about the factors they passed down to their offspring. In the early 1900s, biologists rediscovered Mendel and envisioned those factors as genes. Some believed that genes were merely a mathematical abstraction, while others thought they were physical molecules. But they couldn’t agree on which of the many molecules in the cell were genes. Some thought they were proteins. Others looked instead to a mysterious substance we now call DNA. DNA was made of two strands twisted around each other, each decorated with four molecular units called bases — a four-letter alphabet for writing genes. The crucial step by which a cell turned into two cells was to split those strands apart, and then to add on a second strand to each of them, faithfully copying the script of the original. That discovery unlocked more revelations. In the 1950s and 1960s, Crick and other researchers worked out the code by which cells use the genes encoded in their DNA to build proteins. Other scientists showed how mistakes slip into the sequence of DNA — mutations triggered by radiation and chemicals, for example, or errors that cells made as they copied their own genes. Those mistakes could cause devastating genetic disorders. But they were also the raw material for natural selection. At last, scientists had found a molecular basis for Darwin’s theory of evolution. In 1990, Watson became the first leader of the U.S. government’s effort to sequence the human genome, the three billion base pairs contained in a cell. He only lasted in the job for two years, but the work went on without him. In 2001, over a decade after the project began, scientists finally created the first rough draft of a human genome — an error-riddled collage of several individuals. Genome sequencing became faster and cheaper in the years that followed. Today, a person’s genome can be accurately sequenced in a matter of hours. With the cost of genome sequencing having plummeted to a few hundred dollars, doctors regularly get the genomes of their patients sequenced to check for inherited diseases. Geneticists can probe our evolutionary past by resurrecting the genomes of our ancestors who lived hundreds of thousands of years ago. Watson may have played a crucial part in opening up the modern age of molecular biology, but he embraced some ideas about heredity that existed long before he recognized the double helix. Into his 90s, he spoke both publicly and privately about his conviction that Black people had genes that made them less intelligent than white people. The remarks led Cold Spring Harbor Laboratory, which had appointed him as director in 1968, to sever all ties with him in 2019. “The Laboratory condemns the misuse of science to justify prejudice,” it said in a statement. That prejudice reaches back centuries. In the 1400s, white European Christians began conceiving of themselves as a distinct group of people, superior to other groups. Noble families in Spain proudly declared their ancestry was free of Jewish blood. Native Americans and Africans were considered natural slaves. In the 19th century, early American anthropologists claimed scientific justification for racism in the shapes of skulls. And in the early 1900s, some American scientists asserted that the new science of genetics provided even more justification. Based on that belief, they lobbied for laws to prevent interracial marriages and to allow the sterilization of people deemed unfit. The genome sequencing that Watson helped make possible has given scientists a very different view of humanity. In 2023, for example, the National Academies of Sciences recommended that scientists not use race as a category in genetic studies. They pointed out that traditional racial categories are poor proxies for genetic diversity. Studies on DNA have pinpointed certain genes that have an influence on some measures of intelligence. But the variation in each gene’s DNA sequence only accounts for a tiny amount of the variation in people’s test scores. That’s true of many traits, from height to the risk of heart disease. To understand how our DNA shapes our lives, we have to address the question of how our experience interacts with it. And scientists are still struggling to answer that question. Even DNA itself continues to baffle scientists. If you could stretch out the three billion base pairs in a single human cell, they would measure over six feet in length. But we can’t think of DNA as just a simple line of text containing nothing but recipes for proteins. In fact, our protein-coding genes make up just a tiny fraction of our DNA, while the rest is a confusing wilderness of genetic on/off switches and parasitic bits of DNA, many of which come from viruses that infected our ancestors. And in order to squeeze that six feet of DNA into a single cell, it has to be coiled up in exquisitely complex tangles that change shape from one second to the next. Some scientists are trying to reconstruct the three-dimensional movements of DNA to better understand how cells use it to make the molecules they need to stay alive. With enough hard work, scientists will solve many of these mysteries of DNA. But it will take decades rather than a few years, and the drama will require a cast of scientists far bigger than the one Watson belonged to.
