The usefulness of very old animals

 kw: book reviews, nonfiction, aging, gerontology, longevity

This old fellow, assuming he isn't one of the patriarchs in Genesis, is probably half as old as the tortoise. Among terrestrial mammals, humans have the longest lives. Among all land animals, giant tortoises are probably the longest-lived. It is likely that "Darwin's tortoise" wasn't really brought back from the Galapagos Islands by Charles Darwin, to live to age 175 in a zoo. But it is known that these big tortoises can live at least 150 years, and possibly as long as 200.

No human (at least since the time of Moses) is known to have lived longer than 122 years, the known age of Jeanne Calment, who died in 1997. The second-longest, in the past few centuries anyway, seems to be a living woman currently aged 119. No (recent) man is known to have exceeded 113.

A side note on the great ages reported for Biblical patriarchs. The progression of ages tells a story, which may be more important than whether anyone actually lived 900+ years. What is commonly called "The Fall", the sin of Adam and Eve, is the first of four Falls. Here I'll focus on the longevity of the generations, the story within the story:

1. The first couple disobeyed God and were exiled from the orchards of Eden. Lifetimes went from "undetermined" (potentially endless) to mostly 900-969 years.
2. Cain killed his brother and fled from the presence of God. No lifetime of any of his descendants is recorded.
3. The earth became "filled with violence", motivating God to bring on the Flood, saving only one family. Noah was the last person to live more than 900 years (950). His son Shem lived 600 years, then 3 generations lived 433-464 years.
4. The tower of Babel ("to make ourselves a name") motivated God to confuse the languages. The next five generations lived 148-239 years, ending with Terah (the father of Abram), who lived to age 205.

Each Fall was followed by a reduction in life span by about half. Then Abram/Abraham lived 175 years, Isaac lived 180 years, and Jacob/Israel lived 147 years (his brother Ishmael lived 137 years). Thereafter, a few others including Moses lived to ages of 110 to 120, no more than that. In Psalm 90, composed shortly after God called Moses to return to Egypt, Moses, age 80, declared that the usual life span was 70, or as much as 80 years, "according to strength".

The progressive shortening of life span in Genesis drives home that disobedience to God leads to a shorter life.

Now to the book: Methuselah's Zoo: What Nature Can Teach Us About Living Longer, Healthier Lives, by Steven N. Austad. Dr. Austad is the first professor at his university (Alabama) to hold the Chair in Healthy Aging. His central theme is that nearly all our laboratory studies are of dismally short-lived animals: fruit flies (weeks to months) and mice (less than a year in the wild, less than 3 years in the lab) predominate; but we should be studying animals of exceptional longevity. At least some of them may have something to teach us about living long lives with good health.

Animals with short lives do have a little bit to teach. A mouse in the wild is most likely to wind up being eaten by an owl or a fox. It's well known that larger animals live longer, if only because there are fewer predators that can overcome them. But in a protected laboratory environment, a 3-year-old mouse is positively geriatric: thinning, graying hair; cataracts; feeble gait. Whatever aging is, mice do it fast, like everything else.

The book is full of stories of the unexpectedly long lives of certain animals. It opens with a bird called a fulmar. No firm conclusion is drawn about the longevity of fulmars, but we are introduced to one that might have been nearly as old as the ornithologist pictured with it in two photos taken 35 years apart. The bird outlived the scientist by a year or two, and may have lived 60 years or more. Fulmars are the size of seagulls. We have better information about other birds. A particular cockatoo lived to age 83.

Life in the slow lane can be longer. Tortoises are one example. I have a friend whose pet tortoise, about the size of a softball, was thirty years old the last time I saw him. Giant tortoises live longer, at least the aforementioned 150-175 years. Their heart rate is six beats per minute. Being exothermic (not self-heating like birds and mammals), they have low energy needs. It is said that we each get a potential 2-3 billion heartbeats; for humans that's from 60-90 years. For a giant tortoise, with a heart that beats at 1/10th the rate, maybe they can actually live 600-900 years!

I was intrigued by the animals that don't seem to get feebler with age. Old fulmars and old cockatoos don't have menopause in females (or E.D. in males). Neither do old tortoises. Other long-live mammals and birds do seem to end their lives with a number of years of infertility. I hope there is something useful to learn about genetic (or something else) differences between animals that age and animals that seem not to. It won't come easily or cheaply. Scientists study mice because they don't live long. It's at least 100 times as costly to study lifelong matters with naked mole rats that seem to live 50-100 times as long as field mice. Such studies would be multi-generation endeavors…multi-HUMAN-generation!

Then there's cancer. We don't yet even know the cancer rate for elephants or whales. A bowhead whale, weighs more than 1,000 times as much as a human, and one might naively think they ought to get cancer 1,000 times as frequently. Nope. They live more than 200 years, but we know little more than that. There are a few genetic clues about the cancer-avoiding (not quite cancer-proofing) of huge animals, such has their possession of multiple copies of certain cancer-suppression genes, where humans have one copy only. But our ignorance is typically as colossal as their size.

Even more mysterious are small animals with extraordinary longevity, such as a one-ounce bat that lives 40+ years, or centuries-old mollusks no larger than a teacup. One concept dwelt on throughout the book is Longevity Quotient, LQ. If most one-ounce mammals live at most 3-4 years, and a one-ounce bat species can live 30-40 years, that is an LQ of 10. Humans have an LQ of about 4, although Jeanne Calment's 122-year life indicates an LQ of 5.5.

It is still not known whether there are two intermixed human populations, one with a typical longevity of about 85 years, and another that can make it routinely to 100. I have numerous ancestors who lived into their 90's, and an aunt who died last year at age 101. A friend of mine, who is 65 years old, is already older than everyone in his family tree that he knows about; his parents both lived about 60 years. Maybe there's a third population of shorter-lived humans.

Whatever our ultimate life span may be, recent trends in longevity seem to be based more on health span. Just keeping us from "untimely death" has been a triumph of public health measures including clean water systems, at least in some countries, and vaccination for many former scourges of humanity such as smallpox, measles, and polio. Most of the long-lived ancestors of mine that I mentioned above lived in the 16th, 17th, and 18th Centuries, when such public health measures weren't even dreamed of.

The author makes an important point about "life expectancy", which is different from longevity. Life expectancy is the average age that will be reached by a cohort of the population born at the same time. If infant and child mortality is high, even if some will reach ages greater than 100, the AVERAGE will be low. Population pyramids show this, in part:

A rectangular population pyramid like the one on the left shows that the death rate is low at all ages, until one reaches age 70, and then increases. A triangular distribution, or a "scooped triangle" such as the one on the right, shows a high death rate at all ages. The life expectancy for the US is about 78.5 (average of both sexes). One might initially guess that the life expectancy for DRC is below 30, but we must remember that each horizontal tier is a different cohort. This pyramid shows high death rate, but also high birth rate. The WHO figure for life expectancy of the DRC is 62. That is for the cohort in the bottom tier only, and it takes a lot of actuarial calculation to determine it. Regardless, the more triangular a population pyramid is, the lower the life expectancy. Both charts show a very few people living to 95 and beyond; fewer in DRC than in USA, of course. But there are some. The ultimate longevity in both countries is similar.

This just scratches the surface of a book full of information, well presented. Just finding out how long some animals can live is very time-consuming (decades to centuries!) and can be very costly. The author hopes we will soon begin to learn why some animals live so long. Will learning that help humans become bicentenarians (200+ age)? Perhaps. That makes it worth doing.

One small error I wish to correct. On page 186 it is stated that carbon-14 decays to carbon-12. No, it decays to nitrogen-14, by emitting a beta particle—a high-energy electron—which changes a neutron into a proton. The rest of the analysis in that chapter is correct.