Growing larger everyday, but without growing older
We regularly bait our kids into eating a (relatively) more balanced diet with the promise that they’ll grow up big and tall. While my two-year-old insists he’s already “big,” a key component to their growth lies in the their genes. At a certain point their estrogen levels will fuse their bones’ growth plates, and they’ll be done with linear growth. Since this experience is nearly ubiquitous to humans, it’s strange to realize that not all living things follow this path, with some growing indefinitely.
My, how you’ve grown…
If growth plates didn’t fuse in humans, we might find ourselves in the group of organisms known as “indeterminate growers.” These plants and animals seem to continually grow as long as they’re alive and healthy. The membership is somewhat baffling, and includes sharks, lizards, snakes, and coral, but also mammals like kangaroos. Some plants, like the Rocky Mountain bristlecone pine (Pinus aristata), have been found to have been growing for 4,700 years, although at some point that growth switched from increased height to simply increasing the diameter of the tree’s trunk each year.
You don’t look a day over…
A slight twist on this is creatures that don’t show normal “symptoms of aging.” These organisms, like some tortoises, not only grow slowly throughout their lives, but their organs don’t show expected damage from a lifetime of mutations. One of the most extreme versions of “negligible senescence” is in aspen trees. Clusters of the trees are usually spouts from a single root colony. These clones may live above ground for 40 – 150 years, but the supporting roots live on, possibly up to 80,000 years as far as we can tell. This combination of endless growth and physiological youth has has also helped these aspens become one of the largest living things on the planet.
So does this mean there are lots of immortal giants out there? Not necessarily, although it’s hard to know the age-limits of animals until they’ve expired. When a 20-pound, 140-year-old lobster was caught, it became difficult to know what its natural limits would have been thanks to this moment of human intervention. While sharks grow continuously, many don’t live long in captivity, and those that live in the sea move around so much they’re hard to keep an eye on. Those factors make specimens like Deep Blue, a great white shark estimated to be 50-year-old, a fun surprise we can probably look forward to again in the future.