Sex and Death
The awful existential significance of cellular suicide.
Monday, three biologists won a Nobel Prize in medicine for their work on how healthy cells can deliberately kill themselves. Cellular suicide was first discovered in the early 1970s. Scientists dubbed it apoptosis (AP-o-TOE-sis), a Greek word meaning "falling away," as in petals from a flower or leaves from a tree. Most of us do not worry inordinately about apoptosis. A few brain cells self-destructing here, a few lung cells or muscle cells self-destructing there—what's the difference? We go on living just fine. But, though it may not be obvious from today's news stories about the Nobel Prize, cellular suicide has an awful existential significance. It is the link between sex and death.
For the first billion years after life appeared on Earth, death was a contingent thing. The single-celled organisms that existed back then were essentially immortal. They reproduced over and over again by fission. Given protection from predators and enough food, they never died.
Only when sex entered the picture did death become inescapable. Living things that reproduce sexually have two kinds of cells: germ cells, which are involved in reproduction, and somatic cells, which aren't. The cells in our muscles and brains and hearts and lungs and just about everywhere else are somatic. The DNA in them directs the cell's day-to-day functioning. Over time this somatic DNA accumulates errors in the form of mutations—errors which make it not just irrelevant, but harmful. That is why every somatic cell has embedded in it a self-destruct program—a "death gene." After a certain predetermined span, the cell stops dividing and commits suicide, chewing up its bad DNA in the process.
The DNA in germ cells, by contrast, is destined for the next generation. These cells, which make sperm and ova, have lots of DNA-repair enzymes that prevent the buildup of dangerous mutations. Once enough copies of the germ-cell DNA get out into the world through sex, the somatic cells—which form the structures that make intercourse possible—become just so much excess baggage.
The division of labor between somatic and germ cells is eminently reasonable from the DNA's point of view. From our point of view, it is terrible. Our gonads aside, we are agglomerations of somatic cells. Our brains—the seat of our consciousness, of our selves—are made up of components intent on committing suicide as they become genetic garbage. Even if we evade disease and accident, senescence is sure to set in as more and more of our cells undergo programmed self-extinction. When enough of them die in our critical organs, so do we. As one biologist has put it, "Sex can save our germ cells, but it cannot save us."
One of the three scientists who shared yesterday's Nobel Prize was honored for identifying a death gene that may control cellular suicide in humans. What if this gene could somehow be switched off? Mightn't that be a first step toward bodily immortality? In fact, this seems to be precisely how a certain rather creepy form of immortality was conferred on one Henrietta Lacks of Baltimore. In 1951, Lacks, a mother of four then just entering her 30s, was admitted to Johns Hopkins Hospital with cervical cancer. A piece of her tumor was removed and, as it happens, passed on by the pathologist to a researcher who was trying to grow human tissue in vitro.
The cells from Henrietta Lacks—labeled HeLa—were astonishing. Unlike other human cell lines, which would grow for a while and then peter out, HeLa proliferated nonstop and consumed food voraciously. They seemed to have no senescence clock, no suicide program. Since this made them perfect for studying human cell biology, they were distributed to researchers all over the world. They were even sent into orbit aboard the Discover 17 satellite.
Once introduced into a lab, HeLa cells were so vigorous that they crowded out the other human cell lines. In the mid-'60s, it was discovered, to the horror of medical researchers, that hundreds of published scientific papers supposedly describing how certain heart cells or liver cells behaved were actually about HeLa. Since then the exponential growth of HeLa cells has continued apace. Somehow—scientists are still not sure how—their "death genes" have been deactivated. The number of them around the world today (and in space!) defies comprehension. Each contains a genetic blueprint for constructing Henrietta Lacks—who died in the hospital back in 1951.
This is not the sort of deathlessness anyone desires. We want the immortality of a god, not of a tumor.
In 1929 James Thurber and E.B. White posed a deep question: Is sex necessary? Seven decades later, the answer remains shrouded in mystery. But thanks to the work of yesterday's Nobel laureates and others, we have gained some understanding of a related question: Is death necessary? The answer appears to be yes—because of sex.
Jim Holt is a longtime contributor to The New Yorker—where he has written on string theory, time, infinity, numbers, truth, and bullshit, among other subjects—and the author of Stop Me If You’ve Heard This. He is also a frequent contributor to the New York Times. He lives in Greenwich Village, New York City.
Photograph of Henrietta Lacks courtesy of Harvard News Office.