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Biological immortality is exceptionally rare.
Despite numerous memes that suggest lobsters can live forever, these crustaceans are bound to a mortal existence, just like us.
Discover how long lobsters live, how big they get and why scientists think they don't act their age.
While lots of animals are known as lobsters, for example, spiny lobsters, squat lobsters and slipper lobsters, this term is more formally used to refer to the true lobsters - crustaceans in the taxonomic family Nephropidae.
This is the group that includes well known commercially valuable species such as the European lobster, Homarus gammarus, and American lobster, Homarus americanus.
Working out how old lobsters are can be difficult and scientists have tried a variety of methods. In a lot of other animals, experts can use growth bands left behind on hard structures, such as bones or scales, to determine the age of an individual.
But this method doesn't really work for lobsters. Lobsters shed their entire exoskeleton when they grow and retain no hard structures. The size and weight of the animal helps us guess their age, but it's not a reliable way to determine it accurately.
Instead, scientists tried looking at the fat residue on the eyestalks, assuming older lobsters would have stored up more fat.
They found that, on average, male European lobsters live to 31 years old, and females to 54. There were a few exceptions: one particularly long-lived female had was found to be 72 years old.
Lobsters certainly do not live forever. It's not entirely clear where this myth originated, but it is a claim that persists online, often in the form of memes. While some animals, given the right circumstances, could be considered immortal, lobsters are not among them.
Like many other decapod - ten-footed - crustaceans, lobsters continue to grow throughout their lives. Scientists call this indeterminate growth. This contrasts with people, for example - we stop growing when we reach adulthood.
But lobsters and other decapods do eventually reach the end of their lives.
Lobsters can face death from predation, including by humans, or health issues such as shell disease.
Another potential cause of death is inherently linked to their continuous growth. When they are young, lobsters grow rapidly, shedding their exoskeleton multiple times a year. Over time, growth slows down and moulting becomes less frequent. But for each successive moult, increasing amounts of energy are needed and eventually the cost is too high and lobsters can die from exhaustion. One lobster expert has suggested that that 10-15% of lobsters go out this way.
Lobsters may not be able to grow forever, but they can reach impressive sizes.
American lobsters are larger and heavier than their European relatives. A metre-long specimen, caught off the coast of Nova Scotia, Canada in 1977, weighed in at 20.14 kilogrammes (44lbs 6oz). This is the largest lobster ever caught and currently holds the record as the world's heaviest marine crustacean.
This is not the only big lobster to have been pulled from the ocean. Two individuals from the Virginia Capes, affectionately known as Mike and Ike, are held in the collection at the Museum of Science, Boston. These colossal crustaceans weighed in at 19 kilogrammes (42lbs) and 17.2 kilogrammes (38lbs) respectively.
Rumours of heavier specimens have come and gone. Most have been unconfirmed, such as a 1939 claim of a 21.3-kilogramme (47lbs) giant lobster living off the coast of New Jersey, and a huge 21.7 kilogramme (48lbs) individual said to have been caught near Chatham, Massachusetts.
To imagine just how huge these lobsters would have been, we can compare to ones diners might be familiar with. For example, in Maine, a state with a large commercial lobster industry, there are now fishing regulations that detail a minimum and maximum size for lobsters that can be caught and kept. Any lobsters found to have a carapace - the part of the hardened exoskeleton that protects the head and thorax - of over 12.7 centimetres long must be returned to the ocean. Lobsters this size often weigh around 1.3-1.8 kilogrammes (3-4 lbs).
From the thousands of eggs female lobsters can produce, only a small number will make it to adulthood, and far fewer to extreme sizes.
Biological aging, also known as senescence, is the deterioration of an organism's body and bodily functions, which make it more likely to die and less likely to reproduce.
Aging is complex. There are more than 300 theories that try to explain aging and the mechanisms behind it. However, no single theory is universally agreed upon, so for now it remains a bit of an unsolved mystery.
The many biological aging theories can be broadly divided into two groups: that aging is an inevitable part of life as a pre-programed set of events, or that it is random and caused by life events with the effects accumulating over time.
Lobsters do not show typical signs of senescence. For them, life just goes on until an inevitable end. Unlike people, as they age, lobsters do not weaken, and they continue to grow, feed as normal and reproduce. They can also regenerate limbs if they lose them.
One explanation that emerged in the 1990s centres around lobsters' DNA and their ability to endlessly repair it.
Eukaryotic organisms - this includes animals, plants and fungi - have cells that contain chromosomes, which are structures made up of DNA. The ends of these structures are capped by sequences called telomeres.
Cell division is part of tissue growth and maintenance. Each time a cell divides, the telomeres get shorter. When they are too short the cell enters senescence and can no longer divide.
A study of American lobsters suggested that the reason these animals do not seem to slowdown in old age is due to them having an infinite supply of an enzyme called telomerase throughout their cells. This enzyme is the secret to lobster longevity, extending a cell's life by regenerating telomeres, putting off senescence - like a cellular fountain of youth. This means the cells don't get to the point where they stop dividing.
Humans and other organisms also produce telomerase. But for us, many of the cells that form our bodies lack telomerase activity. Telomerase is expressed in embryonic tissues, stem cells and tumour cells, which corresponds with their capacity to multiply over an extended period.
While lobsters may not be immortal animals that live forever, there are a small number of organisms that have found ways to become biologically immortal, such as Turritopsis dohrnii, better known as the 'immortal jellyfish'. Find out more.
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