zdenek_macat.Stock Brandt's bat (Myotis brandtii) portrait in natural habitat, Shutterstock.
Some creatures live long and stay young
This article focuses on 2 areas:
1) As a general rule, the smaller the size, the shorter the lifespan. However, there are fascinating exceptions to this rule.
2) There are small creatures - like bats, naked mole rats, and grey squirrels - that are known for their remarkable longevity. They live long lives and stay young.
Of mice and men
How many of you - or your kids - have had hamsters as pets? They don't live very long, do they? They are just like mice. Mice only live a few years. For the most part, size is a good measure of a creature's lifespan, as you can see in the graph and data.
Hijab J. Graph of 8 mammalian species: Weight (log) by lifespan (log), August, 2022
MAMMAL | AGE (YEARS) | WEIGHT (KG) |
|---|---|---|
Mouse | 4 (log = 0.6) | 0.030 kg (log = -1.5) |
Dog | 12 (log = 1.1) | 10 (log = 10) |
Cat | 16 (log = 1.2) | 5 (log = 0.7) |
Beaver | 20 (log = 1.3) | 30 (log = 1.5) |
Horse | 30 (log = 1.5) | 600 (log = 2.8) |
Elephant | 70 (log = 1.8) | 11000 (log = 4.0) |
Human | 72.6 (log = 1.9) | 80 (log = 1.9) |
Whale | 200+ (log = 2.3) | 100000 (log = 5.0) |
If you say that mice live shorter lives because they have smaller sizes, you'd be right. The diagram above shows several mammalian species with lifespan on the x-axis and adult weight on the y-axis. Notice that the plots are in logs and rounded off to the next closest log.
Thus, a human lives ~ 70 years and weighs ~80 kg (logs 1.8 and 1.9, respectively). A beaver lives ~ 30 years and weighs ~30 kg (both logs = 1.5). A bowhead whale lives 200+ years and weighs about ~100,000 kg (logs = 2.3 and 5.0, respectively).
Note that the mouse lives at most 4 years (log = 0.6); most mice die young from predators, cold, etc. Even in a protected environment, mice live very short lives.
Larger means living longer (and better):
Small animals live shorter lives than large ones (1-2). Small butterflies live shorter lifespans than larger ones (3). Smaller rodents (like hamsters and mice) live 3-4 years; larger ones, like beavers and porcupines, live 20+ years (4-6).
Part of the relationship between life expectancy and size is logistics. When you achieve a large size, it means that you have had to have the time to get to that size. Baleen whales can weigh almost 100 tons. They keep on growing their whole 200+ years, though at some point there is a limit on size, as the larger sizes reduce efficiency of food acquisition (7).
On a side note, Greenland sharks - while not as huge as whales - have been known to live more than ~300 years (8), increasing their size year by year. The Greenland sharks can reach a weight of 1 ton (1,000 kg).
Being larger usually gives advantages to an animal. Larger animals will generally have less predators, have increased access to food, less competition, increased mating success, etc. Thus, when you take a species, the larger members of that species will predominate over time (9).
Some species are smaller and live long lives:
If you extrapolate and say that all smaller creatures live shorter lives, you'd be wrong. Some species of animals are small and unexpectedlly long-lived. Here are some examples:
- Naked mole rats (30 to 35 gm; ~1.2 oz)--> 30 years
- Blind mole rats (0.1 - 0.57 kg; 3.5 ounces to 1.3 pounds) --> 20 years
- Grey squirrels (0.5 kg; ~ 1.1 lb)--> 24 years
- Chinchillas (weight 0.5 - 0.8 kg; 1.1 - 1.8 lb) --> 10 - 20 years
- Bats (insect-eating Brandt’s bat: 4- 8 gm; 1/4 oz)---> 40+ years
Hijab J. Graph of 12 mammalian species: Weight (log) by lifespan (log), August, 2022
MAMMAL | AGE (YEARS) | WEIGHT (KG) |
|---|---|---|
Mouse | 4 (log = 0.6) | 0.030 kg (log = -1.5) |
Dog | 12 (log = 1.1) | 10 (log = 10) |
Cat | 16 (log = 1.2) | 5 (log = 0.7) |
Beaver | 20 (log = 1.3) | 30 (log = 1.5) |
Horse | 30 (log = 1.5) | 600 (log = 2.8) |
Elephant | 70 (log = 1.8) | 11000 (log = 4.0) |
Human | 72.6 (log = 1.9) | 80 (log = 1.9) |
Whale | 200+ (log = 2.3) | 100000 (log = 5.0) |
bats | 40 (log = 1.6) | 0.004 - 0.008 kg (log = - 2.2) |
squirrels | 24 (log = 1.4) | 0.5 kg (log = - 0.3) |
blind mole rats | 20 (log = 1.3) | 0.3 kg (log = -0.5) |
naked mole rats | 30 (log = 1.5) | 0.030 kg (log = - 1.5) |
A naked mole rat is roughly the same size as a mouse (about 30 grams or the weight of 1 slice of bread) lives more than 30 years versus the mouse's lifespan of 3 - 4 years.
The insect-eating Brandt's bat is about 0.25 oz or 1.5 teaspoons in size. Some of those very long-lived Brandt’s myotis bats roost in caves in Siberia. In 2005, a bat was captured for examination; it had a numbered band that had been placed on it in 1964. That bat was at least 41 years old (10). The old bat was checked out and released back into its cave.
They live long and stay young most of their life
The thing is: who wants to live forever if one is old and frail. The trick is to live a long life and stay young.
For mice - assuming they survive the harsh external environment in their first 1-2 years - they start aging when they turn 1 and 1/2 years (or in their 40s and 50s). By the time they reach 2 years of age (or in their 60s), they are considered very old; they have cancer, heart disease, arthritis, and kidney disease (11 - 14).
Mouse with Walker, Nadia Johnson, Aug, 2022
I don't know about you, but I have never seen a bat using a walker.
Bats and naked mole rats seem to have discovered how to conquer the double dread of aging and disease. They stay young for most of their lives; they seem to be immune to cancer and many of the diseases that afflict mice and men (15- 17).
Next article: Average lifespan for most animals is under 30 years
What is the average lifespan for animals?
In the next article, I will describe average lifespans for many creatures on our planet. I will touch on creatures that consistently beat the average, and stay young and fertile for most of their lives.
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