As a bodybuilder, lifeguard, and gym owner, Larry the Lobster is an iconic character in the SpongeBob cartoon series. While this classic show isn鈥檛 known for its scientific accuracy, it at least gets right that lobsters live on the ocean floor. These arthropods are members of the subphylum Crustacea, characterized by having a segmented body with an exoskeleton and jointed limbs. Larry seems to have maintained his macho-man lifestyle since the show鈥檚 inception in 1999, never losing his youthful persona. Is this realistic? Interestingly, lobsters don鈥檛 show typical signs of aging.
For this reason, there is often debate as well as confusion about lobsters being immortal. Biological immortality means that the risk of death is not linked to chronological age. The claim of lobster immortality is due to their apparent continuous growth. It鈥檚 as if we kept growing way past our twenties, never showing signs of wrinkling or weakening.
So why do we stop growing, while lobsters don鈥檛? The cells that make up our body are constantly making new cells by dividing. A biological technicality causes us to lose a bit of DNA at the ends of our chromosomes (structures made up of DNA and proteins) after each replication. DNA contains the blueprint for our lives, so in order to make sure we aren鈥檛 losing crucial information during these divisions, the long molecules of DNA are protected by shorter segments of DNA at their ends called 鈥渢elomeres.鈥� An analogy would be the plastic tips on a shoelace that prevent it from unraveling. When a cell multiplies, the only part of the chromosome that is lost is a piece of the telomeres. But as we age, our telomeres get shorter, until they reach a critical point where the cell can no longer replicate without damage to its essential DNA. When this occurs, the cell becomes inactive or dies. Shortening of telomeres is linked to senescence and increased risk of disease. Other contributors to aging include oxidative stress (hence the appeal of antioxidants).
Lobsters have a perpetual supply of telomerase 鈥� the enzyme that can restore telomeres, helping cells avoid that fateful end. Humans also have telomerase, just not enough to overcome the constant shortening of telomeres. In fact, telomerase is often found in cancer cells, giving tumours a survival advantage.
Unfortunately for our pal Larry, a large supply of telomerase can be a double-edged sword. Lobsters are still more likely to die with age because their hard-shell exoskeleton moults and has to be regrown. This requires reams of energy, eventually too much. As a result, common causes of death for lobsters are exhaustion, immobility, and shell disease, although the leading cause is still predation.
An easy way to estimate the age of a lobster is to simply check its size. But there鈥檚 a much more accurate alternative. Lobsters have growth rings around their eye stalks that reveal their precise age 鈥� much like tree rings! Evidence shows a new ring is formed annually on calcified regions of the eye stalk, which is the stem-like structure connecting the eye to the head. The rings, viewable under a microscope, are also formed in calcified regions in lobsters鈥� gastric mills 鈥� the 鈥渢eeth鈥� in their stomachs.
So, it turns out lobsters aren鈥檛 immortal after all -- otherwise they would have an endless number of growth rings! If this news upsets you, there is a biologically immortal jelly fish, Turritopsis dohrnii, that can restart its own life cycle, rather like a phoenix. Of course, no matter how long-lived, it can still be killed 鈥� that鈥檚 just the cycle of life and death.
Haleh Cohn just finished her first year at 成人VR视频 and is interested in the health sciences.
