Live Long and Prosper

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Yet each of those “twigs,” each plant and animal on Earth, sharing a given place and a given time is driven by its own species’ biological clock, is traveling on its own genetically pummeled path from birth to death. Think of that: All in the blink of an eye, so much going on. For some, life is exceedingly short — only minutes for some bacteria, less than a day for an adult mayfly, perhaps a week for the luna moth. Those ladybugs we played with had but a few months of life beyond pupal infancy, while Bonnie and I had barely begun our species’ expected journey of three score and ten years. Those maples, I like to think, will still be standing half a century from now.

This swirl of varying life spans in nature, say biologists, is essential not only to each species’ survival but to the health of whole ecosystems.

Every multicelled organism’s life span is marked by three phases: embryonic, juvenile and adult. In the last phase, the individual reaches a reproductive peak of some duration or other, and then — well, the truth is it’s all downhill from there.

It’s a good thing, too — as long as you look at it from an objective, scientific viewpoint. Over the eons, each species’ characteristic life span has been delimited by the forces of survival and natural selection. Those forces, driven by sexual reproduction that yields succeeding generations of genetically unique but mortal individuals, have allowed the species to adapt to ever-changing environmental conditions. Immortal plants and animals, on the other hand, would be stuck in a genetic rut, susceptible to and ultimately doomed by change.

And then, of course, there is the more pragmatic purpose of a limited lifetime: Without death, there would soon be no room or resources for new generations.

So we live, reproduce and die, each of us — every plant and animal on Earth — in cadence to our species’ internal clocks.

But because we all share space and time with other creatures, our paths entwine, one influencing the other. The owl’s sharp-taloned swoop for sustaining protein brings a vole’s march through life to a screeching halt. A robin feeding its young: so long, squirming worm. Fly meets flycatcher. Little fish meets big fish. Green beans meet gardener. Each link in the food chain is forged by the premature end of one life to fuel another’s travels through time.

This partly explains why biologists distinguish between potential or maximum life span — how long a plant or animal can live under ideal conditions, with only its own clock to contend with — and “average,” or actual life span: the length of time an organism generally can be expected to survive in the wild. As you can see from the chart below, the two can be many years apart — in some cases, several real-world lifetimes.

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