When I was studying bacteria, I learned that single-celled organisms have no concept of life span. Single-celled organisms continue to multiply by dividing repeatedly, so their cells seem to be continuous. When they reproduce sexually, the number of divisions is reset, so in theory they can divide infinitely. This makes me wonder what life span is.
https://manabu-biology.com/archives/
Each time the cells of animals and plants divide, the protein structures at the ends of chromosomes called telomeres become shorter, and when they become shorter to a certain extent, cell division stops. The length of telomeres varies from species to species, and the way they are reduced also seems to vary considerably from species to species. It is thought that the length of telomeres and the way they are reduced determine the approximate lifespan of each species.
https://www.fish.lif.kyoto-u.ac.jp/telomere.html
Among living things, there is a creature called Turritopsis nutricula that can repair shortened telomeres and rejuvenate itself. Turritopsis nutricula repeats the process of rejuvenating itself into a young state called a polyp after becoming an adult and reproducing sexually, resulting in a state called immortalized traits. Here too, there seems to be no concept of lifespan. Living things are mysterious.
https://stemcells.or.jp/turritopsis-spp
Other long-lived creatures include the mussel, a bivalve that can live for over 500 years, a glass sponge that was found to be 23,000 years old, and a horn coral colony that is thought to be about 7,000 years old. The longest-lived vertebrate is the Greenland shark, which lives for over 400 years, the Galapagos tortoise for over 250 years, and the bowhead whale for over 200 years. Is there any connection between longevity and the sea?
https://nazology.kusuguru.co.jp/archives/86062
There is an impression that there are many long-lived plant species as well; Posidonia oceanica seagrass is said to be 100,000 years old, Jomon cedar is 2,170 to 7,200 years old, and Welwitschia is 2,000 years old.
https://karapaia.com/archives/52161609.html
On the other hand, there seem to be many insects with short life spans, especially sea midges, which take about three weeks to reach adulthood and only live for about an hour after they reach adulthood. A life span of one hour is quite shocking. Here are some other insects that are thought to have short life spans. Cicadas reach adulthood in about six to seven years and have a life span of about two weeks, mayflies reach adulthood in about a year and have a life span of a few days to about a week, and fireflies reach adulthood in about a year and have a life span of a few days to about two weeks. Some mammals and reptiles seem to have a life span of just a few months. I wonder what a life span is.
https://etervalu.com/2017/02/05/ephemeral-animals
Some creatures have no concept of lifespan, while others have extremely short lifespans. This made me wonder what lifespan really is, and what life and death are. I feel like it’s something that can’t be understood with everyday senses, but perhaps this is also the mystery of life. Lifespan is amazing. Life on Earth is amazing.
