Biological immortality (sometimes referred to as bio-indefinite mortality) is a state in which the rate of mortality from

senescence Senescence () or biological aging is the gradual deterioration of Function (biology), functional characteristics in living organisms. Whole organism senescence involves an increase in mortality rate, death rates or a decrease in fecundity with ...

(or aging) is stable or decreasing, thus decoupling it from

chronological Chronology (from Latin , from Ancient Greek , , ; and , ''wikt:-logia, -logia'') is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of events. It is also "the deter ...

age. Various unicellular and multicellular species, including some vertebrates, achieve this state either throughout their existence or after living long enough. A biologically immortal

living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organisms ** Living species, one that is not extinct *Personal life, the course of an individual human's life * ...

being can still die from means other than senescence, such as through

injury Injury is physiological damage to the living tissue of any organism, whether in humans, in other animals, or in plants. Injuries can be caused in many ways, including mechanically with penetration by sharp objects such as teeth or with ...

poison A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...

disease A disease is a particular abnormal condition that adversely affects the structure or function (biology), function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical condi ...

predation Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

, lack of available resources, or changes to environment. This definition of

immortality Immortality is the concept of eternal life. Some species possess "biological immortality" due to an apparent lack of the Hayflick limit. From at least the time of the Ancient Mesopotamian religion, ancient Mesopotamians, there has been a con ...

has been challenged in the ''Handbook of the Biology of Aging'', because the increase in rate of mortality as a function of chronological age may be negligible at extremely

old age Old age is the range of ages for people nearing and surpassing life expectancy. People who are of old age are also referred to as: old people, elderly, elders, senior citizens, seniors or older adults. Old age is not a definite biological sta ...

s, an idea referred to as the late-life mortality plateau. The rate of mortality may cease to increase in old age, but in most cases that rate is typically very high.

Cell lines

Biologists chose the word "immortal" to designate cells that are not subject to the Hayflick limit, the point at which cells can no longer divide due to DNA damage or shortened

telomere A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see #Sequences, Sequences). Telomeres are a widespread genetic feature most commonly found in eukaryotes. In ...

s. Prior to Leonard Hayflick's theory, Alexis Carrel hypothesized that all normal somatic cells were immortal. The term "immortalization" was first applied to

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

cells that expressed the telomere-lengthening

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

telomerase, and thereby avoided

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

—i.e. cell death caused by intracellular mechanisms. Among the most commonly used cell lines are

HeLa HeLa () is an immortalized cell line used in scientific research. It is the oldest human cell line and one of the most commonly used. HeLa cells are durable and prolific, allowing for extensive applications in scientific study. The line is ...

and Jurkat, both of which are immortalized cancer cell lines. These cells have been and still are widely used in biological research such as creation of the

polio vaccine Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated vaccine, inactivated poliovirus given by injection (IPV) and a attenuated vaccine, weakened poliovirus given by mouth (OPV). The World Healt ...

, sex hormone steroid research, and cell metabolism. Embryonic stem cells and

germ cell A germ cell is any cell that gives rise to the gametes of an organism that reproduces sexually. In many animals, the germ cells originate in the primitive streak and migrate via the gut of an embryo to the developing gonads. There, they unde ...

s have also been described as immortal. Immortal cell lines of cancer cells can be created by induction of oncogenes or loss of tumor suppressor genes. One way to induce immortality is through viral-mediated induction of the large T-antigen, commonly introduced through simian virus 40 (SV-40).

Organisms

According to the Animal Aging and Longevity Database, the list of animals with negligible aging (along with estimated longevity in the wild) includes: * Blanding's turtle (''Emydoidea blandingii'') – 77 years * Olm (''Proteus anguinus'') – 102 years * Eastern box turtle (''Terrapene carolina'') – 138 years * Red sea urchin (''Strongylocentrotus franciscanus'') – 200 years * Rougheye rockfish (''Sebastes aleutianus'') – 205 years * Ocean quahog clam (''Arctica islandica'') – 507 years * Greenland shark (''Somniosus microcephalus'') - 250 to 500 years

Bacteria and some yeast

Many unicellular organisms age: as time passes, they divide more slowly and ultimately die. Asymmetrically dividing

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

and

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

also age. However, symmetrically dividing

and

can be biologically immortal under ideal growing conditions. In these conditions, when a cell splits symmetrically to produce two daughter cells, the process of

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

can restore the cell to a youthful state. However, if the parent asymmetrically buds off a daughter only the daughter is reset to the youthful state—the parent is not restored and will go on to age and die. In a similar manner

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell ...

s and

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s can be regarded as "immortal".

Hydra

Hydras are a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of the

Cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

phylum. All cnidarians can regenerate, allowing them to recover from injury and to reproduce asexually. Hydras are simple,

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

animals possessing radial symmetry and contain post- mitotic cells (cells that will never divide again) only in the extremities. All hydra cells continually divide. It has been suggested that hydras do not undergo

, and, as such, are biologically immortal. In a four-year study, 3 cohorts of hydra did not show an increase in mortality with age. It is possible that these animals live much longer, considering that they reach maturity in 5 to 10 days. However, this does not explain how hydras are subsequently able to maintain

lengths.

Jellyfish and comb jellies

'' Turritopsis dohrnii'' and '' Turritopsis nutricula'', are small () species of

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

that use transdifferentiation to replenish cells after

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

. This cycle can repeat indefinitely, potentially rendering it biologically immortal. These organisms originated in the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

, but have now spread around the world. Key molecular mechanisms of its rejuvenation appear to involve

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all life, living organisms, acting as the most essential part of heredity, biolog ...

and

repair The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure and supporting utilities in industrial, business, and residential installat ...

, and stem cell renewal, according to a

comparative genomics Comparative genomics is a branch of biological research that examines genome sequences across a spectrum of species, spanning from humans and mice to a diverse array of organisms from bacteria to chimpanzees. This large-scale holistic approach c ...

study. Similar cases include

hydrozoa Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...

n '' Laodicea undulata'', scyphozoan '' Aurelia'' sp.1 and tentaculata '' Mnemiopsis leiydi''

Lobsters

Research suggests that lobsters may not slow down, weaken, or lose fertility with age, and that older lobsters may be more fertile than younger lobsters. This does not however make them immortal in the traditional sense, as they are significantly more likely to die at a shell moult the older they get. Their longevity may be due to telomerase, an

that repairs long repetitive sections of

DNA sequence A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the nu ...

s at the ends of chromosomes, referred to as telomeres. Telomerase is expressed by most vertebrates during embryonic stages but is generally absent from adult stages of life. However, unlike vertebrates, lobsters express telomerase as adults through most tissue, which has been suggested to be related to their longevity. Contrary to popular belief, lobsters are not immortal. Lobsters grow by

moulting In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...

, which requires considerable energy, and the larger the shell the more energy is required. Eventually, the lobster will die from exhaustion during a moult. Older lobsters are also known to stop moulting, which means that the shell will eventually become damaged, infected, or fall apart, causing them to die. The European lobster has an average life span of 31 years for males and 54 years for females.

Planarian flatworms

Planarian flatworms have both sexually and asexually reproducing types. Studies on genus '' Schmidtea mediterranea'' suggest these planarians appear to regenerate (i.e. heal) indefinitely, and asexual individuals have an "apparently limitless elomereregenerative capacity fueled by a population of highly proliferative adult stem cells". For sexually reproducing planaria: "the lifespan of individual planarian can be as long as 3 years, likely due to the ability of neoblasts to constantly replace aging cells". Whereas for asexually reproducing planaria: "individual animals in clonal lines of some planarian species replicating by fission have been maintained for over 15 years".Archived a
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References

Bibliography

* James L. Halperin. ''The First Immortal'', Del Rey, 1998. * Robert Ettinger. ''The Prospect of Immortality'', Ria University Press, 2005. * Dr. R. Michael Perry. ''Forever For All: Moral Philosophy, Cryonics, and the Scientific Prospects for Immortality'', Universal Publishers, 2001. * Martinez, D.E. (1998) "Mortality patterns suggest lack of senescence in hydra." ''Experimental Gerontology'' 1998 May;33(3):217–225
Full text.
* {{DEFAULTSORT:Biological Immortality Immortality Senescence