Quick overview of what you will learn from this blog post:
- The animals which show that aging is not inevitable
- An animal that is biologically immortal
- What we can learn from them to slow down aging
What if we told you that aging is not inevitable? You would probably be a bit skeptical, right? We have all heard similar claims from cosmetic companies over the years, so such a reaction is totally understandable. We get it.
So, why do we believe that aging is not inevitable?
First things first: we know it isn’t because nature shows us it isn’t. There are a number of species that do not appear to age and there are even some that appear to be biologically immortal. Read on!
The naked mole rat does not appear to age
The naked mole rat is probably the best-known example of an animal that does not appear to age. They can live 30 or more years (no joke!) and they remain fertile and do not become frail during this time. This is impressive when you compare this to other rodents of a similar size that live only 2 or 3 years.
Unlike humans, naked mole rats don’t experience an increased chance of dying as their age increases. In humans, a person’s risk of dying doubles roughly every 8 years beyond the age of forty. Naked mole rats have no increased risk of death even though they are 25 times older than when they reached sexual maturity.
Researchers believe that one of the reasons for this longevity and agelessness is the mole rat’s superior ability to repair DNA damage. This makes sense given that genomic instability is one of the proposed reasons we age.
Lobsters also do not seem to age
Some lobsters do not show the typical signs of aging. For these animals, life goes on until disease or predation catches up with them. Unlike us, lobsters do not weaken as they grow older and they continue to grow and reproduce the same as younger members of their species.
Similar to mole rats, it appears that lobsters are very good at repairing their DNA which may be the key to how they get older but do not suffer from the debilitating effects of aging.
Lobsters (just like us) have chromosomes, which are structures made up of DNA. The ends of these chromosomes are protected by caps known as telomeres, these are protective structures made from repeating sequences of DNA. As we age these caps wear away until there is none left and the cell stops dividing and dies, this shortening of the telomeres is believed to be a reason we age.
But the lobster has no such limitation thanks to having a continual supply of the enzyme telomerase. This enzyme is able to keep replacing the telomere cap as fast as it can be worn down, allowing the lobster cells to keep on going. In a way the lobster carries around its own fountain of youth!
Humans also have telomerase, but the majority of our cells cannot access it with the expectation of some populations of stem cells and embryonic cells during development. It is thought that our cells are prevented from accessing telomerase as an anti-cancer measure as tumor cells hijack telomerase in order to become immortal and grow without control.
Somehow the lobster has evolved so all its cells can access telomerase and it also manages to avoid cancer allowing it to avoid aging and live for a hundred or more years.
There are more animals that do not appear to age like us
There are quite a number of animals that do not seem to age (several displayed in the chart below). The lifespan stated in this chart is also based on documented sources, it is quite possible that some individuals of each species could live even longer but their age has not been recorded.
| Species | Known Lifespan |
|---|---|
| Naked mole rat | 30 Years |
| Sea anemones | 80 Years |
| Lobsters | 100 Years |
| Lake sturgeon | 152 Years |
| Clams such as Panopea generosa | 160 Years |
| Rougheye rockfish | 205 Years |
| Freshwater pearl mussel | 250 Years |
| Aldabra Giant Tortoise | 255 Years |
| Greenland Shark | 400 Years |
| Ocean Quahog clam | 507 Years |
Senescence vs negligible senescence
As time passes, science is also discovering more animals that do not age like we do, but how do they do this?
The gradual deterioration associated with aging is known as senescence and happens in the majority of species. It describes a decline in survival characteristics including strength, mobility, cognition, sense, as well as an age-related increase in mortality. There is typically also a loss of reproductive capacity during senescence.
Ok, so that makes sense and is probably how most of us understand aging. But here’s where things start to get weird and why we say that aging is not inevitable…
There are animals that buck the senescence trend and appear not to really age. Such animals enjoy what science calls negligible senescence. That means they experience no decline in survival characteristics, no increase in disease incidence, and no rise of mortality as they age. They are also able to reproduce just the same as younger animals of their species do.
If animals not aging was not weird enough for you, things get even weirder. Some animals are so good at avoiding aging that they take things a step further.
Some animals may effectively be biologically immortal
The hydra is named after the sea monster from Greek mythology, which regrows its heads if one is cut off. However, the real life freshwater hydra puts the mythological creature to shame with how good it is at regenerating. In fact, it is able to regenerate so well that even a small piece of tissue can become a full hydra in just a few days.
It belongs to the genus Cnidaria phylum, a group of species which all share the ability to regenerate. This allows them to recover from injury and they are all able to reproduce asexually. The genus includes such diverse species including jellyfish, hydra, sea anemones, and corals.
In a four year study, 3 groups of hydra were monitored and they showed no increased risk of death regardless of increasing age. This is interesting when considering these animals reach sexual maturity within 5-10 days.
It is likely the animals would have continued to remain alive much longer, if not indefinitely, if given the right environment and nutrition.
The same researchers then did a follow-up study with 2,256 hydras kept in ideal conditions, safe from predation. Water was changed three times a week and they were given fresh brine shrimp for nutrition. Eight years later, there was absolutely no sign of senescence in the animals.
Death rates were highly stable with just one hydra in every 167 dying each year, this was regardless of their age. Fertility remained good for 80 percent of animals, the remaining 20 percent saw fluctuation in reproductive ability (this was likely due to conditions in the lab).
All things considered, the hydra is probably biologically immortal.
Learning from the hydra
So, how does the hydra regenerate so efficiently? Better yet, what can we learn from it? The secret lies in its stem cells according to a study that saw researchers exploring just how the hydra regenerates.
Stem cells are the foundation stones of our body. They reproduce fresh replacement cells which can become any type of specialized cell needed through a process called differentiation. This is how we as humans and indeed other animals can maintain our tissues and organs and recover from injury.
Unfortunately, unlike our friend the hydra, our stem cells lose their ability to work properly as we age and eventually, they cease to function and produce fresh cells. Hydra stem cells are different, they do not suffer from age-related decline and continue to powerfully regenerate and produce fresh cells indefinitely.
Essentially with hydras there is a continual turnover of their cells. They effectively replace their entire bodies every few weeks which allows them to discard aged and damaged cells. This constant cycle of replacement means old cells do not get to hang around and the hydra does not experience age-related decline.
A hydra is made from three cell lineages: ectodermal epithelial, endodermal epithelial and interstitial. All three types of stem cells share a common protein: FOXO. This protein may at least partially explain why the hydra can avoid the effects of aging and enjoy negligible senescence.
It is also worth noting that humans who live beyond 100 often have variants of the FOXO gene. This also means the FOXO gene and protein are potential therapeutic targets for interventions to slow down aging.
Bottom line? This goes to show that aging is certainly not the norm, and we should not consider that it is the default by any means. These findings also fly in the face of the old assumption that all animals must decline with age.
There are quite a few species that have powerful regenerative ability and, if we can understand and harness it, we may be able to slow or halt aging like they do. At the very least if we can make our own stem cells less prone to age-related decline, it could mean a longer healthy lifespan.