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They heard motors and saw three high-speed gray inflatables speeding into the cove, toward them.

“Yes,
Enterprise!
That is understood.” Gritting his teeth, Captain Sol turned off the radio. “Damn it, Cynthea, what now?”

TONIGHT’S FIRE-BREATHING CHAT:
WHY WE DIE
by Dr. Geoffrey R. Binswanger

Once again, Lillie Auditorium
was packed to the rafters on a crisp autumnal Thursday night.

The lights dimmed and Geoffrey strode out onto the stage wearing yellow sneakers, jeans, his Kaua’i T-shirt, and a lime-green velvet Nehru jacket with red piping.

“Good evening, ladies and gentlemen. Why does a Galapagos tortoise live a hundred and fifty years, a mayfly a single day, and a human being rarely past the age of eighty? Is it simply because our parts wear out at different rates? Or is there a reason, or even some evolutionary advantage, for the very shortness of life? And if there is some positive biological purpose, does this mean the clock can be reset, presuming evolution has used some mechanism to ‘set’ the timer of life in the first place?”

Geoffrey clicked the remote. A close-up of an egg timer on a 1950s-style kitchen counter appeared behind him, to a smattering of nervous chuckles.

“The question I want to pose and offer a possible answer to tonight is:
Could the speed with which death arrives have a survival advantage?
On its face, it seems like a ridiculous notion, but I believe there might be a very simple explanation for the variation in animal life spans: Animals may actually grow old and die only to
prevent
them from breeding with their own offspring.”

Geoffrey clicked to a picture of Cousin Itt from
The Addams Family.
A few laughs bubbled up from the audience.

“Of course, we have had strict taboos against incest since time immemorial. Indeed, parent/child breeding causes particularly disastrous damage to the genetic integrity of almost all life on Earth, causing sterility in both plants and animals in only a few generations. Prior to human taboos, nature may have enforced its own taboo by imposing life spans to prevent that genetic catastrophe from occurring.”

Geoffrey clicked again. A scene of microscopic cells on a blue field appeared.

“In the ancient seas of Earth where DNA first formed and single-celled life helped replicate it for over a billion years, there was no need to limit life span. Bacteria and most cells did not even reproduce sexually, and if they did, the chances of encountering one of their own progeny were practically nil. Scientists have speculated that certain forms of bacteria may actually be immortal. In the year 2000, researchers at West Chester University found bacteria that had remained alive for two hundred and fifty million years, locked inside salt crystals buried deep underground.”

Geoffrey clicked to a picture of a terrarium overcrowded with hamsters.

“But animals with access to much smaller breeding groups have a problem. The more offspring they have with each pregnancy, the more serious the threat to the gene pool they become, unless DNA protects itself by implanting a time bomb in such
animals set to go off before cross-generational breeding can occur.”

The next slide showed a close-up of a pier piling stacked with mussels.

“To see if such a correlation might hold true, I began comparing animal life spans to their reproductive behavior. Mussels may live up to a hundred years. They live in colonies and simultaneously mingle billions of sex cells into the seawater to reproduce. With the tide flowing in one direction during their synchronized spawning and the sheer multitude of participants, the chance of incestuous reproduction is virtually nonexistent. No discernible life span is present. Giant clams, which reproduce much the same way, can live five hundred years. Tubeworms thriving near thermal vents at the bottom of the sea and many corals that reproduce this way are believed to live for centuries.”

Geoffrey clicked to another close-up image.

“Barnacles, on the other hand, also live in colonies but have life spans of only one or two years. Why? Barnacles reproduce in a very different way. Male barnacles extend penises nine times the length of their bodies, longer than any penis relative to body size in the animal kingdom, in order to copulate with other barnacles.”

Amusement fluttered across the audience. Geoffrey laughed.

“Size may matter, but not that much. Barnacles necessarily have a very small group of breeding partners. The risk of cross-generational breeding is high enough to require them to die before a second generation is ready to breed. Death occurs at about twice their breeding age.”

Geoffrey clicked to another image: the vast trunk of a California sequoia fringed by ferns.

“Conifers, the first trees to use pollen to reproduce, did so before the help of insects. Like coral reefs, they had to spew vast clouds of sex cells into currents of air flowing over forests, making it nearly impossible for cross-generational breeding to occur. We know of bristlecone pines nearly five thousand years old, and giant sequoias, cedars, and the New Zealand kauri pine are some
of the longest-living organisms on Earth. In 2008, researchers discovered a thriving spruce tree nearly
ten thousand
years old.”

The next slide showed what looked like a giant scowling rat. Its naked tail was coiled around the branch it was climbing. Miniatures clung to its underside and back.

“Opossums, the only North American marsupial, are solitary, don’t migrate, and stay in the same neighborhood throughout their lives. They have up to thirteen young in a litter, which reach sexual maturity after only one year. If there was ever a case that could make cross-generational breeding possible, this is it. But since opossums don’t just play possum but actually die at only one to two years of age, no cross-generational breeding can occur.”

The next close-up image set the audience squirming in disgust.

“The humble earthworm, on the other hand, exists in vast numbers, makes no social connections, and constantly shuffles the deck of its breeding partners. Its life span is about a decade.”

The slide of a tiny furry mammal elicited cooing noises from the auditorium.

“Voles, which eat earthworms, are tiny mammals that live in communal burrows and reproduce rapidly; they live only two to six months before shuffling off their cute and fuzzy little mortal coils. Considering the frequency of their mating and the early age they reach sexual maturity, that’s just in the nick of time.”

A wave of revulsion rippled through the room as the next slide showed the caramel bead of an insect head that was seemingly being squeezed out of a large waxy bag of flesh.

“Queen termites,” Geoffrey said, “are monogamous. Together with the king termite, they generate tens of millions of offspring over the course of their lives. About the same size as the vole that lives only one hundred days, queen termites may live one hundred
years.”

The next slide was an image of Bugs Bunny, which got a laugh.

“Cottontail rabbits are legendary breeders that live in small warrens, all marks against them, if this principle is correct. They live twelve to fifteen months on average, and thirty-five percent of them die in the first month. Interestingly, rabbits in captivity
can live eight to twelve years. And if they are spayed or neutered, up to twice that, since their risk of cancer is greatly reduced by the procedure.”

A slide showed a whale’s fluke dripping a beaded curtain as it arced over the sea.

“Blue whales have ninety-year life spans. They travel in pods of relatively small number, like rabbits; but unlike rabbits, they congregate in vast numbers to breed. This shuffling of the deck during mating season reduces the odds of cross-generational breeding to near-zero. Bowhead whales may live more than two hundred years. We have found living individuals with stone arrowheads, which have not been used since the 1800s, still lodged in their flesh.”

Geoffrey proceeded to click through a gallery of animals.

“One of the most prolific congregators is the normally solitary whale shark. They can’t even breed until they are thirty years old, and they do so in large groups off the coasts of Mexico, Australia, the Seychelles, and East Africa as they follow their seasonal breeding tour like a social calendar of endless mixers. Whale sharks live more than a hundred and fifty years.

“Spiny lobsters also congregate, marching in great single-file conga lines across the ocean floor to breeding zones every year. They may reach ages of fifty years or more if they don’t wind up on a dinner plate first.

“Sea turtles, which live eighty years and sometimes more than a hundred and fifty years, travel thousands of miles to congregate and shuffle the genetic deck. The giant tortoises on the Galapagos and Seychelles live in vast colonies year-round and are famously long-lived.

“Squirrels, however, don’t congregate or migrate—and predictably live only one to two years, or twice the age they reach sexual maturity. In captivity they may live up to fifteen years. So, obviously, biological life span is balanced against life span in their natural habitat. No need to limit life span biologically if predators are already doing it. So long as all the knobs are set to prevent cross-generational breeding, the genetic line remains healthy.”

Geoffrey clicked from a close-up of a chubby squirrel to a portrait of a croaking frog.

“Bullfrogs live up to sixteen years in the wild, ten years on average—five times longer than squirrels. But why wouldn’t they have even longer life spans, given this equation, since they have access to large numbers of breeding partners, as do mussels, pine trees, and tortoises? After all, each female bullfrog lays up to twenty thousand eggs at a single spawning, and they live in vast numbers within proximity to one another. They make no social bonds. The chances of them mating with offspring seem similar to those of other animals that live in vast colonies.

“Bullfrogs fall victim to predators more frequently than whales or giant tortoises do, of course, and must replace themselves faster to survive as a species. But the answer, I believe, lies in the fact that bullfrog habitats don’t necessarily provide access to large breeding pools. Bullfrogs frequently get isolated in ponds as water levels recede. In the worst-case scenario, with one male and female bullfrog sharing one pond, the female may produce twenty thousand chances for cross-generational breeding if the parents live long enough. So why don’t bullfrogs have short life spans? Because their offspring swim as polliwogs for an amazing
five years
before becoming frogs and reaching sexual maturity. Thus, they are five when they mate, as their parents die at ten, twice the age of sexual maturity.”

Geoffrey clicked to an image of a stork couple in a great nest atop the chimney of a Swiss chateau, the Alps shining in the background.

“Monogamous birds like white storks, bald eagles, and Canadian geese live up to three decades. The monogamous ostrich lives fifty to seventy-five years, with pairs observed breeding together for forty years. Many subspecies of wild turkey, by contrast, do not congregate or migrate and are not monogamous. They live only two to three years in the wild. The Asian house mouse, which breeds promiscuously within a small social group, lives one year; the monogamous deer mouse, native to the United States, lives seven years. But what happens if all the rules are violated?”

The image on the screen was now a sitting cheetah, its fur ruffled by wind as a storm cloud darkened the sky behind it.

“The cheetah lives about ten years in the wild. Female cheetahs reach maturity at two years, males at one year. This is unusual, since females of most animals generally reach sexual maturity first, a staggering that helps prevent cross-sibling breeding in animals that have multiple offspring simultaneously. Yet, strangely, male cheetahs don’t get the chance to breed until their third year, as they stay with their mothers far longer than females. This, by the way, is a phenomenon also observed among certain species of graduate student.” He smiled as his audience roared with laughter. “This means cheetah offspring have two years to breed with their own mother.”

A resounding “Yuck” came from the audience.

“This appears to contradict the principle altogether. And perhaps with disastrous results. The cheetah, one of the oldest species of cat, enjoyed large breeding groups during its four million years of evolution. But now that its habitat has been fragmented and breeding partners greatly diminished, cheetahs are inbreeding at an alarming rate, threatening the entire species as offspring become susceptible to disease and infertility. It is thought that at some point in the past cheetahs faced a very near extinction event, so that all existing cheetahs have descended from as few as one breeding pair. If so, the same cheetah behavior that may have saved the species then may threaten it now.”

Geoffrey clicked to a new slide.

“African elephants live in small groups. They do not congregate to breed, but they can live up to sixty years. How can this be? First of all, seventy percent do not survive to reach thirty, and half die by the age of fifteen. And, though female elephants become fertile at twenty, and males reach maturity at about age fourteen when they either leave the herd or are forced out by the females, male elephants remarkably do not breed until their
thirties
, when they have finally attained the size and skill to compete with other successfully breeding males. Thus, elephant social behavior avoids the possibility of cross-generational breeding
through what I have dubbed the ‘ late-bloomer’ effect. As with hippos, whales, and bullfrogs, delaying the breeding age increases life span while not violating the principle that
life span equals no more than twice breeding age.”

A slide of bundled-up revelers giving thumbs-up in Times Square appeared.

“Throughout human evolution, the life span of our ancestors never averaged much more than thirty years. Human groups rarely exceeded two hundred individuals during the millions of years of our evolution, and were often much smaller. Such a very small gene pool invites genetic compromise. Human males reach sexual maturity at about the age of fifteen, females reach maturity between the ages of eight and fourteen. This leaves a seven-year window of opportunity for parent/offspring mating and seemingly violates the rule.