Human beings, especially animals, age and die. Fungi, too, can age. In contrast, many species can be considered immortal: for example, bacteria fission to produce daughter cells, strawberry plants grow runners to produce clones of themselves, and animals in the genus Hydra have a regenerative ability by which they avoid dying of old age.

Early life forms on Earth, starting at least 3.7 billion years ago, were single-celled organisms. Such organisms (Prokaryotes, Protozoans, algae) multiply by fission into daughter cells; thus do not age and are innately immortal.

Aging and mortality of the individual organism became possible with the evolution of sexual reproduction, which occurred with the emergence of the fungal/animal kingdoms approximately a billion years ago, and the evolution of seed-producing plants 320 million years ago. The sexual organism could henceforth pass on some of its genetic material to produce new individuals and could itself become disposable with respect to the survival of its species. This classic biological idea has however been perturbed recently by the discovery that the bacterium E. coli may split into distinguishable daughter cells, which opens the theoretical possibility of "age classes" among bacteria.

Even within humans and other mortal species, there are cells with the potential for immortality: cancer cells which have lost the ability to die when maintained in a cell culture such as the HeLa cell line, and specific stem cells such as germ cells (producing ova and spermatozoa).In artificial cloning, adult cells can be rejuvenated to embryonic status and then used to grow a new tissue or animal without aging. Normal human cells however die after about 50 cell divisions in laboratory culture (the Hayflick Limit, discovered by Leonard Hayflick in 1961).

At present, researchers are only just beginning to understand the biological basis of aging even in relatively simple and short-lived organisms such as yeast. Less still is known of mammalian aging, in part due to the much longer lives of even small mammals such as the mouse (around 3 years). A model organism for studying of aging is the nematode C. elegans. Thanks to its short lifespan of 2–3 weeks, our ability to easily perform genetic manipulations or to suppress gene activity with RNA interference, or other factors. Most known mutations and RNA interference targets that extend lifespan were first discovered in C. elegans.

Regards
John George
Journal of Aging Science