The human bias makes us want to discuss the longest living creatures, so we'll invert that and start with the shortest. Mayflies are often cited as having the shortest lifespan on Earth, lasting only 24 hours, but the extreme case is the adult female Dolania americana which lives for less than five minutes. It has vestigial mouth parts and can't even feed itself, so it's only job is to reproduce.
Mayflies are called 'one-day insects' but it's misleading because the mayfly is the adult form, and they have lives before they metamorphose from larvae. The award should probably go to a type of marine gastrotrich (also known as 'hairybacks') which live only three to 21 days.
Orange Roughy fish can live 149 years so, if you eat one, it's probably older than you. Usually the bigger a creature is, the longer its life span, and a Bowhead Whale can live 211 years. An exception is Ming the clam, an Ocean Quahog that was dredged off the coast of Iceland, aged 507.
The human bias also focuses us on animals, but we are easily outlived by some types of plants. The Bristlecone Pine named Prometheus was at least 4844 years when it was cut down in 1964. The oldest living thing known is a Quaking Aspen tree colony in the Fishlake National Forest in Utah aged about 80,000 years.
Most life forms (prokaryotes like bacteria and archaea) do not have a life cycle and do not have programmed death. They just divide in two. They can be killed by smashing them or starving them but they don't have a "life span" like humans have.
Dr Charley Lineweaver, from the ANU Research School of Earth Sciences, links death to the process of evolution. "This is a difficult question and has to do with the origin of sex ... sex and programmed death evolved together."
About 2 billion years ago, with the invention of sex, cells differentiated into germline cells (sperm, egg) and somatic cells (the other cells in your body). This is the evolutionary origin of the death of bodies. The somatic cells became mortal, while the germline cells remained immortal.
Sex is how genes are mixed, and death weeds out those that are less adapted to an environment. The process of evolution needs the genetic variation made possible by sex and death.
Different species have different reproductive strategies. Ecologists call "R" types those with shorter life spans, and which breed rapidly. They are the early adapters, rapidly exploiting a new niche. Live fast, die young. The "K" strategists are slower growing. They are in for the long haul. They live longer and have fewer offspring.
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