HOW OLD DO MAMMALS GET?

by Whit Gibbons

August 13, 2017

All around the globe, people are living longer than their ancestors did. In the U.S. this means the entire age structure of our population is shifting. Healthier diets and more exercise are partly responsible for our increased longevity, and modern medicine certainly helps keep more people alive for a longer time.

But no matter what we do, old age finally catches up with us. Even the healthiest, most active people eventually show signs of senility.

Scientists do not fully understand the aging process, and National Institutes of Health funding for medical research on the phenomenon of aging in humans is mostly reserved for studies conducted on the usual laboratory animals: white rats, white mice, rhesus monkeys, chimpanzees, fruit flies. I have a suggestion for NIH: Channel more money for studies on aging ecologists doing research on senescence – or the absence thereof – in various animals. These study subjects are not the typical laboratory specimens, and none have the physiological similarities to humans that rats, mice and primates do.

But they have traits that might provide researchers with a better understanding of the process of aging.

For example, albatrosses apparently live for more than 50 years, maybe even a hundred, yet do not show the typical signs of senescence so common among humans. A female albatross begins laying about one egg a year at the age of 10 and continues to do so. Presumably, a 75-year-old albatross is as reproductively fit as a youngster of 45 or 50, showing no signs of reproductive failure. Clearly, the albatross holds some secrets we might like to know more about.

Spiders are another group with unusual aging traits. Most spiders live a couple of years, not such a surprising feat, but some tarantulas have been known to live for 35 years. One reason tarantulas may be a useful research tool is that the males and females differ considerably in their longevity patterns. Upon reaching maturity, the female tarantula continues to molt, grow and reproduce. The male on the other hand, upon reaching spider manhood at 10 years of age, mates once or twice and then dies within a year or two. In the human population, females live slightly longer than males. The dramatic difference in mortality rates of the sexes in tarantulas offers opportunity to identify a specific cause of the consistently earlier death of males. Perhaps a lesson for humans will emerge.

In contrast, possums could provide useful information toward understanding senescence and some of the associated problems that accompany old age because of their relatively short lifespans, which average less than 2 years. A 3-year-old possum teetering on the edge is likely to have cataracts, reproductive senility and other signs of aging found in humans. The oldest known possum lived for 6 years and 7 months in the Little Rock Zoo.

The book “Longevity of Mammals in Captivity” by Richard Weigl is a remarkable compilation of all of the documented oldest recorded ages of the world’s mammals. Most live longer in captivity than in the wild, offering researchers the opportunity to examine the aging process in long-lived individuals. Many chimpanzees have surpassed the half century mark, as have several elephants, some living to be more than 60. Great apes like gorillas and orangutans often live into their 50s.

Surprisingly, one of the oldest documented ages for a mammal, other than humans, belongs to a Florida manatee born in the Miami Seaquarium in 1948. It died this year – at age 69! Not only that but the manatee did not die of old age but in an accident. Research on these, and many other species, might be able to tell us something about our own aging processes.

Meanwhile, as we wait for medical research to add a few more years on to our lives, we should heed the words of George Bernard Shaw: "We don't stop playing because we grow old; we grow old because we stop playing."

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