Immortality

Age catches up with us all eventually, as it does for almost all types of organism. Bodies accrue damage over time, triggering the slow decline we know as senescent ageing. Organisms senesce because every living thing, regardless of its condition, must succumb sooner or later to the caprices of its never-quite predictable environment. Against this reality, a winning strategy lives extravagantly, letting the cost of current excesses accumulate into the future when death might anyway intervene to cancel the debt. For every organism, life means having potential to create new life1, even though the effort only hastens their senescent decline. We may each burn our allotted candle at both ends, yet life itself manifests inexhaustibly2.

Some remarkable organisms seem to escape ageing. The Blue Mountains fungus Armillaria ostoyae, the White Mountains bristlecone pine, the Mojave desert creosote bush, a bdelloid rotifer, the campion Silene stenophylla, the hydroid Turritopsis dohrnii, a virus and certain microbes – all of these species have evolved exceptional defences against environmental hazards. Their winning strategies prioritises survival over reproductive rate, with lifetime productivity as the criterion of success. For as long as life keeps spawning life with lower death rates, natural selection may favour ever slower senescent ageing3, resulting in extraordinary lifespans for some individuals or genets4. Despite their vastly prolonged vitality, true immmortality still eludes them. Even under utopian conditions of indefinite fecundity, “senescence will tend to creep in”5 for them as for us and no matter our yearnings for eternal youth.

Milestones in evolution and history

• Life first emerged on Earth about 4 billion years ago and has persisted ever since, through all of the last quarter of the existence of the Universe.
• Natural selection on heritable adaptations of individuals to their environment drives speciation of populations through time (Darwin, 1859), resulting in the wondrous diversity of life on Earth. By far the greatest threats to this biodiversity are the coupled actions of anthropogenic climate change and habitat conversion to agriculture and industry.
• The stem Cnidaria evolved 635 million years ago, ancestors of biologically immortal marine hydroids.
• Extraordinary lifespans: a 1,900 year-old fungus, a 4,700 year-old bristlecone pine, an 11,700 year-old creosote bush, a 24,000 year-old bdelloid rotifer, a 32,000 year-old campion plant, a 48,500 year-old giant virus, 101.5 million-year old aerobic microbes.
• Hamilton, W.D. (1966) The moulding of senescence by natural selection. Journal of Theoretical Biology, p. 25. One possible escape from senescent ageing presents itself in densely crowded and stable populations, which can favour runaway selection on an ever more thinly spread age profile of fecundity and a correspondingly ever-reducing senescence, even to the point of biological immortality (Seymour and Doncaster 2007).

C.P. Doncaster, Timeline of the Human Condition, star index