Secrets of the Ages: A wide-ranging look at the puzzle of longevity, which varies across species in often confounding ways

FEBRUARY 24, 2014, 4:09 PM  1 Comment

Secrets of the Ages

By ABIGAIL ZUGER, M.D.

The Science of Life Span and Aging. By Jonathan Silvertown. University of ChicagoPress. 208 pages. $25.

Think too much about your life span and you will never get out of bed in the morning. Once you do, though, all the scientific mysteries of the subject may lie panting on the rug at your feet. Why should your good old faithful dog (avid exerciser, nonsmoker, nondrinker) be condemned to age and die after barely a decade, while you remain firmly in your prime — and the neighbor’s African gray parrot lives loudly on and on?

Jonathan Silvertown has managed to distill the thousands of years of thought and research behind this and many related biologic questions into a small book so captivating and enlightening that — unusual for a volume packed with difficult scientific concepts — you will read it for pure pleasure, even though it provides remarkably few solid answers.

In other words, Mr. Silvertown, a professor of ecology at Britain’s Open University, will not teach you how to live forever. Rather, he swoops like a barn swallow (life span 16 years) across a terrain encompassing the long-lived ponderosa pine (300 years) and the evanescent nematode worm C. elegans (days to weeks), with nods to Oliver Wendell Holmes Jr. (93 years), Dylan Thomas (49 years) and Woody Allen (still ticking) to demonstrate why, even though you personally are probably limited to less than a century, you are still a particularly lucky conglomeration of organic matter in life’s long mortal parade.

“The puzzle of longevity,” Mr. Silvertown points out, “is not why we die so soon but rather why we live so long.” For most of history, living creatures were single cells that reproduced by dividing. But once evolution produced multicellularity, reproduction and survival were separated, and hemmed in by new risk-benefit calculations. Cell division had to persist for purposes of reproduction and repair, but it also had to be controlled, for uncontrolled division means cancer (“a brutal reminder that long life is a precarious achievement”).

The cancer cells of Henrietta Lacks (immortalized in laboratories everywhere, as well as in Rebecca Skloot’s best-selling book) demonstrate that under the right circumstances, mammalian cells can survive more or less forever. But the life span of whole beings is inextricably linked to nutrition, environment and genetics, all operating under an evolutionary mandate to optimize the species.

In animals, large size roughly correlates with long life. How peculiar, then (and still unexplained), that the winner of the longevity sweepstakes is at the moment neither giant whale nor tortoise but a507-year-old ocean quahog clam, while a little naked mole rat can live decades longer than its bigger rodent relatives.

Birds live longer than similar-size mammals (and birds that can fly live longer than ones that can’t — eluding predators always helps). And yet when researchers play God and impose terrible external disasters on a flask full of fruit flies, the survivors live shorter lives than would be expected. Is it because they reproduce earlier, somehow sensing their jig may soon be up?

Life span among plants ranges from the flash-in-the-pan annuals, with gorgeous blossoms followed by quick demise, and the ridiculously long-lived conifers that endure for centuries or more. But, as Mr. Silvertown points out, most of the essential structural matter composing these massive survivors is actually dead. And then there is a scrubby South African tree that may be tens of thousands of years old, repeatedly sending up new sprouts from an ancient subterranean root. Do those trees count as old even though they’re young? From such paradox is the science of mortality created.

But be honest, it’s the human part of all of this that really interests you — you and generations of financial entrepreneurs, some of whom, as Mr. Silvertown details, experienced various costly confusions about the statistics of their enterprise. (For the record, life insurance salespeople should bet on longevity, peddlers of annuities just the reverse.) Modern experts may be clearer on the calculations, but many important predictors of human survival have not changed for centuries: To live long it helps to have long-lived parents, and being female doesn’t hurt, provided childbirth doesn’t kill you.

Otherwise senescence (a precise statistical term in life-span circles describing the increasing likelihood of death) is inevitable. Granted, it is not as immediate as it used to be — over the last two centuries our own species has increased its average life span by nearly a quarter. And yet we demand more, with various trendy techniques for outliving your neighbors, over which Mr. Silvertown casts a biologist’s skeptical eye.

The new vogue for drastically limiting calorie consumption to increase life span, for instance, reminds him of nothing so much as a longevity gene in C. elegans that apparently works by damping down metabolism, creating a dormant worm called the dauer (from the German for “endure”). Humans who elect to starve themselves, he points out, “feel perpetually cold, are understandably short of energy and have low libido, symptoms that have an uncanny resemblance to the dauer state of C. elegans.”

Mr. Silvertown’s narrative ends with the newest elements of modern longevity science: telomeres and telomerase, oxidative stress and free-radical dependent repair. They are concepts that clarify some details but then obscure others, leading, much like the circle of life by 13th-century savants laid out on the mosaic floor of Westminster Abbey, both backward and ahead. It is a glorious, mysterious cycle Mr. Silvertown presents, one that demands enthusiastic rereading.