Jonathan Silvertown’s The Long and the Short of It: The Science of Life Span and Aging explores the study of longevity from the perspective of natural history and considers the cases for aging, heredity, and decay via stories about the senescence of potatoes, water fleas, dragonflies, men, women, bacteria, poets, and kings. Along the way, Silvertown addresses key concerns, such as: What causes again, and what determines the length of an individual life? If the lifespan of our species is increasing so dramatically, why haven’t we evolved to become immortal? The below excerpt introduces the foundation of his argument (here, both literal and figurative), beginning with a rumination on the Great Pavement of Westminster Abbey:

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Sooner or later, everyone ponders their mortality. It is the privilege of youth to be oblivious to death, but the fate of old age to contemplate oblivion. Each person searches for answers in his or her own way, but eventually all ask the same questions: How long might I live, and why must I die? What rhyme or reason is there in aging or mortality? Long before science offered reasons, art sought a rhyme that would give meaning to the mysteries of life and death. Such a rhyme is hidden in a priceless and little-known work of medieval art that lies before the high altar of Westminster Abbey in London, England.

Hidden for decades beneath a carpet that used to be rolled back only for the feet of a new monarch, the Great Pavement of Westminster Abbey is a gloriously intricate mosaic floor that depicts a medieval view of the cosmos. It connects the life spans of plants, animals, and people with the life span of the universe and the day of judgement that would herald its end. The story told in the Great Pavement cannot now be read on its damaged surface, but it has been reconstructed by historical and archaeological detective work. An inscription in Latin, which ran around the four sides of the square frame that encloses the pavement, tells us that the mosaic was completed in “this Year of Our Lord 1272,” in the reign of King Henry III. The pope contributed to the cost of its construction, and the Italian artisans who laid its dazzling pattern brought with them to dismal London bright stones salvaged from ancient Roman floors: glass tesserae in cobalt blue, turquoise, red and white, and purple porphyry, the livid color of congealed blood. This last is the rarest of the stones in the Great Pavement, found in only one mine in Egypt that closed 500 years before the birth of Jesus.

Within the square frame is a design of four circles that flow into one another, like giant loops formed from a single cord. Around the perimeters of the circles once ran the words:

If the reader wittingly reflects upon all that is laid down,
he will discover here the measure of the primum mobile:
the hedge stands for three years,
add in turn dogs, and horses and men,
stages and ravens, eagles, huge sea monsters, the world:
each that follows triples the years of the one before.

Primum mobile refers to the outermost heavenly sphere in the medieval conception of the universe. Thus, according to the inscription, the witting reader will discover in the Great Pavement the measure of the universe or, in other words, how long it will endure. The medieval designers of the Great Pavement knew that different animals and plants have different life spans, and they perceived this variation as part of the grand design of the cosmos itself. The linked circles in the pavement embody the idea that life cycles are yoked together and are linked to the longevity of the universe. Everything was connected by application of the holy number three, culminating in judgment day. The formula that links the life spans in the pavement is three years for a hedge (before it is rejuvenated by cutting), tripled, which gives 3² (= 9 years) for the supposed life span of a dog; tripled again for the life span of a horse 3³ (= 27 years), and so on up to 3 to the power 9, or 19,683 years, for the duration of the primum mobile.

Nineteen thousand years must have seemed like a very long time to a medieval cosmologist, but we now know that, looking backward into Earth history, it is scarcely any time at all. The Devonian limestone in the pavement, a rock consisting mainly of fossilized remains of marine creatures, is on the order of 350 million years old, but life has been present on Earth for ten times longer than that (3.5 billion years), and the planet is a billion years older still. The universe is nearly 14 billion years old by current estimates. Although today we are asking the same questions about time that our medieval forebears did, the answers offered by science stretch the imagination to its very limits.

What has science to say about life spans? Why do different species live for such different lengths of time—a dog for maybe 10 years, but a human for 80? Medieval cosmologists believed that there was unity in the diversity of life spans because all belonged to a divinely ordered mathematical series. Does science have its own unified explanation for why longevity varies, or is just a giant heap of facts, like a pile of mosaic pieces lacking order or design? And what of aging—the dysfunctions that accumulate with age and that terminate even the longest life? Why do we age? Do animals and plants grow decrepit just as we do?

This book is my own mosaic in which I will piece together the answers that modern science offers to these questions.

Read more about The Long and the Short of It here.