Fruit flies have a life span of just one month, but earthworms live for ten years — and parrots can reach the ripe old age of 100 (Fig. 1). Generally speaking, the longest-living members of the animal kingdom tend to be the less highly evolved ones. For example, a koi carp in Japan has been proven to be 226 years old, while an Aldabra giant tortoise (Fig. 1) in an Indian zoo was discovered to be 256, and a mussel, the Icelandic cyprine “Ming” is — believe it or not — 507 years old.
The longest-living species within the various animal families are often found in the coldest climates. For example, whales and sharks usually live to be around 100 years old. However, the bowhead whale (title picture), which makes its home in Arctic waters, has a maximum life span of over 200 years, and the ground shark (Fig. 1) can live to be over 400 years old. Cold climates go hand in hand with greatly reduced bodily activity and a slower metabolism, both of which could play key roles in ensuring a longer life.
A question of bodily size
When it comes to mammals, the bodily warmth required to sustain life plays a decisive role in determining maximum life span. Heat loss depends on the size of the physical surface relative to the body’s volume. The larger the animal, the more favorable this ratio and the lower the metabolic rate, meaning the total energy turnover throughout the bodily mass. That’s why larger mammals live longer than smaller ones do. Interestingly, if you multiply an animal species’ metabolic rate by its maximum life span, you get the same figure across the board, whether you’re looking at a mouse or an elephant: specifically, around 220 kilocalories per gram. It’s as though each animal species has the same amount of “life force.” If the animal has a more vigorously physical lifestyle, it burns through this capital more quickly.
The vigorous lifestyle is reflected in factors such as differing pulse rates. A mouse’s heart beats 500 times per minute (if there are no cats around), whereas an elephant’s heart beats around 26 times a minute (Fig. 1). Extrapolating this figure to the maximum life span of a mouse (four years) and for an elephant (70 years) yields the same result, astoundingly: A mammal’s heart beats 1’000’000’000 times before falling silent.
Humans form the exception to the rule
Those of us who might be tempted to calculate our own number of heartbeats will be horrified to find that we should actually be dead a long time ago. Since our hearts beat 75 times a minute, we would reach our billion heartbeats at the age of 20. Luckily, though, we generally live four times longer than that (if we act responsibly, of course). At 122 years of age, the French woman Jeanne Calment (1875–1997), the oldest known person, has surpassed biological expectations six times over. How has Homo sapiens managed to evolve to enjoy such a long life span? Researchers are still pursuing answers to this question. One probable cause is the strongly delayed bodily development seen in humans at birth and during their first few years of life. This also causes humans to stay youthful — and, therefore, capable of learning and adaptation — for longer than other mammals do.
Plants barely move, have no pulse, and continually regenerate the majority of their body parts. So they can live far longer than people or animals do. Trees, in particular, can enjoy astonishingly long lives. Cherry trees can live to 400, spruces can live to 1’100, and fig trees can even live up to the age of 2’000. In 2012, an ancient intermountain bristlecone pine (Fig. 2) was discovered in the White Mountains of California. As dated by its rings, this tree is now 5’070 years old. The cold climate in these mountains supports its longevity. It also helps that it has a summery growing season of a mere three months and the minimal amount of local pests.