The Nature Corner: Aging
By Ernie Marshall
Some years ago, I took a walk along a stretch of Reedy Branch, a tributary making its way to the Tar River, with a tree specialist to pick his brain about the trees we encountered. There were a lot of old trees, “virgin forest” perhaps since the area was once farmland back when farmers didn’t attempt to clear and farm the bottomlands or floodplains. We talked about the different look of aging trees, coming near the end of their lifespan of a century or more. Their crowns thin out, less full with fewer branches and less foliage, they often develop some lean, no longer have that straight and tall look and the oaks and hickories no longer bear nuts. They seem to look old, as if imitating our changes with age, a bit bent over and balding. They even seem to get a look of wisdom earned with age. Everything in nature ages just as do we.
Some trees are quite aged, being the oldest living things on Earth. Redwoods get to be at least 2000 years old and sequoias over 3000. Both are topped by the bristle pine, which lives 5000 years or more.
Longevity in nature is a very wide spectrum. Most herbaceous plants live only a few months, then disperse seeds to start anew. Many insects live only a matter of days or weeks. The tiger swallowtail sipping nectar in your garden may be gone tomorrow. At the other extreme, stars go through a cycle from birth to demise that lasts billions of years, when they burn all of their hydrogen and perhaps go out with a bang as a dazzling supernova. (No cause for alarm, our sun should last another five billion years, being about half way through its life span.)
Aging is not to be confused with immortality, the fact that all of us will die at some point. Aging is part of life, death is life’s opposite. We tend to think that we fear our own death. Perhaps what we fear is dying, an end stage of the life process. I think the first century B.C. Roman philosopher Lucretius summed it up by saying we have nothing to fear in our death, because “when I am here death is not, and when death is here I am not.” Mark Twain puts it this way: “The fear of death follows from the fear of life. A man who lives fully is prepared to die at any time.”
To make more interesting comparisons between the life spans of living things and get closer to home, let us consider what has been called the “heartbeat hypothesis” that all mammals – whose longevity ranges roughly from the pygmy shrew that lives only a year or so to the bowhead whale that may live 200 years – live for the duration of about one billion heartbeats.
Consider the following instances:
Pygmy shrew – 1.02 billion total heartbeats (1300 bpm, 1.5 year average lifespan)
Mouse – 1.31 billion (500 bpm, 5 years)
Cat – 1.18 billion (150 bpm, 15 years)
Human – 2.24 billion heartbeats (60 bpm, 71 years)
Horse – 0.93 billion (44 bpm, 40 years)
Elephant – 1.03 billion (28 bpm, 70 years)
Notice that the larger the animal gets, the slower its pulse rate. A cat is roughly 100 times larger than a mouse, but its heart rate is about a third as rapid as that of the mouse. The pygmy shrew, with it very rapid pulse, burns itself out in a year or so.
Note who breaks the “one billion heartbeat rule” — us, humans. We get something like twice what other species get. If we followed the rule, our life expectancy would be 35 years instead of 71 years. (It is commonly thought that human life span has increased through history. It seems not, that the Bible “three score and ten” is fairly constant, considering only death “from old age,” not disease, accident, death in tribal warfare, death in childbirth, etc.).
There is a plethora of hypotheses about why our species is an exception to the “one billion heartbeat rule.” I will leave you to ponder or research this. I would like instead to ponder the “one billion heartbeat rule.”
Heartbeats seem a better measure of life than years, the pulse of a life sustaining organ in our bodies, rather than Earth’s annual trip around the sun. All of a sudden we have a yardstick for the lives of us and our fellow mammals. Or do we?
My dog Bullitt ages at about seven times the rate that I do. Does that mean because of his more rapid heartbeat (and metabolism) that he experiences time differently? Does his lifetime feel as long as mine? Does he experience a difference in my wife and I being away for an hour for an errand and our being a way for a weekend? Humans seem hyperconscious of time. We make plans for the future and remember the past (or worry and regret). Does my dog just “live in the moment,” an ever-repeated present?
Despite our dependence on watches and calendars, the experience of time with humans is largely subjective. An hour spent in a hospital waiting room for news about cancer or a newly arriving baby seems much longer. An hour with a cherished friend seems much briefer.
And since Einstein, there is no longer a cosmic yardstick in physics for the universe at large for measuring time. (The question “what time is it on the moon?” is totally meaningless.)
Oh my, a stroll along a stream bank looking at trees has led us to bumping into Albert Einstein. Time to conclude this column. May you have a long life, age well and fill your time with bright and memorable moments.
Ernie Marshall taught at East Carolina College for thirty-two years and had a home in Hyde County near Swan Quarter. He has done extensive volunteer work at the Mattamuskeet, Pocosin Lakes and Swan Quarter refuges and was chief script writer for wildlife documentaries by STRS Productions on the coastal U.S. National Wildlife Refuges, mostly located on the Outer Banks. Questions or comments? Contact the author at firstname.lastname@example.org.
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