Death may be an inevitable part of life, but aging may be another matter entirely. How fast we age depends on a host of factors, including sex, family, work, childbearing, and most importantly, genetics.
"Somehow, the same genetic machinery, inherited from our common ancestors at the dawn of life on Earth, has been molded to generate life spans ranging from hours (yeast cells) to thousands of years (sequoia trees and quaking aspen)," write Josh Mitteldorf and Dorion Sagan in Nautilus.
The "genetic machinery" also determines not only how fast we age but also "the pattern of deterioration" over that time, the authors write. "Aging can occur at a steady pace through the course of an entire lifetime (most lizards and birds), or there can be no aging at all for decades at a time, followed by sudden death (cicadas and century plants)."
Does that mean that aging and its subsequent deterioration aren't as inevitable as they seem?
Humans are among the most adaptable life forms on the planet, capable of living in the most extreme environments. We are also incredibly fertile. Our instincts to protect and nurture the next generation mean that more of our young survive to adulthood and consequently live to breed.
Breeding appears to play an outsized role in the aging process.
Aging to death can be rapid and sudden at the end of a reproductive cycle. Sudden post-reproductive death is common in nature, affecting organisms as varied as mayflies, octopuses, and salmon, not to mention thousands of annual flowering plants. Biologists refer to this life story as “semelparity” (from Latin “single birth”).
The cause of death in semelparous organisms varies widely. Octopuses just stop eating. Praying mantis males make an ultimate reproductive sacrifice, giving themselves up as snacks to their female partners. Salmon destroy their own bodies with a blaze of steroids.
Then there's the Turritopsis nutricula, a kind of jellyfish that has a unique way of dealing with aging; it doesn't.
The adult Turritopsis has inherited a neat trick: After spawning its polyps, it regresses back to a polyp, beginning its life anew. This is accomplished by turning adult cells back into stem cells, going against the usual developmental direction from stem cells to differentiated cells—in essence driving backward down a one-way developmental street. Headlines called Turritopsis the “Benjamin Button of the Sea.”
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The point is that aging in any certain way is not guaranteed. I think most people would prefer to enjoy life physically and mentally right up to the point we keel over. Could there be a combination of drugs and genetic alterations that could allow us to be perpetually sixtyish?
Why is there a menopause? We care for our young and our extended families, and our devotion continues after our children have grown and become parents themselves. Hence, the standard explanation for life that continues after fertility ends is called the “grandmother hypothesis.” Women have a genetic interest in seeing their grandchildren grow up healthy. Maybe at age 60 they can contribute more to their own genetic legacy by caring for their grandchildren than by having more babies of their own. This is a hypothesis that sounds reasonable, at least for humans, but a number of demographic researchers have found that when they do the numbers, it’s hard to make it work.
Aging is built into all creatures' DNA, but animals age at different rates. Some animals stop eating when they stop breeding. "Mayflies entering adulthood have no mouth or digestive system whatever," note the authors.
Can humans ever get control of the aging process? Would it be possible, like Turritopsis, to turn back the hands of time and begin life anew? Given our adaptability, anything is possible when it comes to human life.
