The idea of extending the average human lifespan is a common feature of science fiction as well as fantasy and urban fantasy. The introduction of non-humans with very long lifespans, or even true immortality, is also common. For example, R.A. Heinlein’s Lazarus Long, C.J. Cherryh’s Cyteen, J.R.R. Tolkien’s elves (immortal) and dwarves (long lived), or any urban fantasy writer’s vampires.
Because of its prevalence, there are a wide variety of options that can be played with as part of the concept.
Extended Life versus Immortality
There is a difference between an extended lifespan and immortality. Someone whose lifespan has been extended will eventually die of natural causes, because they continue aging and the body will eventually break down. On the other hand, an immortal individual will never die of old age. Either version may or may not include immunity to disease, immortality usually does.
There are also three major varieties of life extension and immortality that can come into play:
Extended Life—The individual ages and gets progressively older, but lives longer.
Slowed Aging—The individual ages, but at a significantly slower rate than other people; ex. the individual ages one year for every five that pass.
Unaging—The individual never ages beyond a certain point, usually achieving adulthood or being turned into an immortal.
Once the decision between extended life and immortality is made, there are other questions. The most important is how does the life get extended or why is the character/species immortal. Literature and movies give us thousands of possibilities for achieving an extended life, from medicine to alchemy, natural genetics to magic items.
There are also several different kinds of immortality:
Alchemical Immortality—A common element of Western and Asian, particularly Taoist, legend is the elixir of life, an alchemically brewed drink that prevents death so long as the individual drinks it on a regular basis. Ex. Nicholas Flamel (Rowling & Scott), the Taoist Immortals.
Ascension—Some sources discuss the option of ascending to a higher, usually non-corporeal, plane of existence and state of being, often through enlightenment, to achieve immortality. Ex. Bodhisattvas, The Ancients (Stargate).
Food-Based Immortality—Many mythologies around the world refer to specific foods that give the eater immortality. Ex. the Norse gods and Idun’s apples, the Chinese Peaches of Immortality.
Item-Based Immortality—Occasionally we come across stories in which a magical item confers immortality upon the owner, usually this is seen as a curse and the item cannot be removed or discarded.
Location-Based Immortality—Sometimes, an individual attains immortality, but only while (s)he remains in a given place; if the individual leaves that place, then they age at an accelerated rate until reaching their true age. Ex. the Grail Knight in Indiana Jones.
“True” Immortality—Nothing is required for this immortality to come into effect, usually this means the immortality is genetic in nature. Ex. Tolkien’s elves.
Undeath—An arguable immortality occurs when the individual achieves a state between life and death. Ex. ghosts, liches, the Norse draugr.
Vampiric Immortality—Individuals attain and maintain immortality by feeding on others, whether feeding on blood, emotions, or other life forces.
In all cases, there are some biological and psychological effects to extended lifespans and immortality that should be considered.
Maturation is perhaps the first biological effect that comes into play. With some sources of immortality or extended life, this is not an issue. When, for instance, an individual achieves immortality through alchemy, a magic item, or a location, then maturation is not an issue. For those who achieve immortality or long life naturally, some age normally until adulthood, then stop or slow down. Others have slowed aging from the start, ex. D&D non-humans.
Psychologically, there is the question of how the mind contains and processes the memories and information acquired over centuries or millennia. For non-humans, the simple answer is that their minds naturally evolved to adapt to their extended lives. For humans, whether they reach immortality through alchemy or becoming a vampire or other means, most writers and worldbuilders come to the conclusion that eventually the weight of processing centuries of memories and information would become too much. This could lead to mental breakdowns or other issues. Some handle this potential problem by using torpor. If applied, this means the immortal occasionally enters a semi-hibernation state, whether willing or otherwise, during which they rest apart from society. This has the effect of preserving the mind and avoiding ennui on the part of the individual. It also serves to allow the society to evolve and others to shape or lead society.
Alongside the personal effects, immortality and extended life, particularly on a widespread scale, are bound to have social effects.
Governance—The governance of society is an important issue, particularly if there is widespread immortality. Is there static, staid leadership that causes society to stagnate or are there artificial mechanisms in place to ensure change? For example, among Tolkien’s elves, both Elrond and Galadriel ruled their respective peoples for millennia in lands that effectively never changed, which was one reason they had to leave Middle-Earth.
Inheritance—If a significant number of people in society never die (of old age) or take centuries before succumbing to age, do their descendants ever inherit their worldly possessions? When? How?
Reproduction—If an immortal species can reproduce rapidly, they are very likely to overrun the world in a short time. This is one reason that many worlds with vampires include societal laws regarding who can create new vampires and when. On the other extreme, even an immortal species that reproduces too slowly will eventually die out. Balance between the two extremes seems to be key.
Social Climbing—Without natural death, or centuries between natural deaths, is it possible for individuals to climb in society? Usually, in mortal societies, openings in the social status structure are created through death or retirement. If we remove one or both of those, then society is heavily affected. Some artificial measures can evolve in society to solve the problem, including challenges and assassination, of opening up positions at the top of the social heap.
Social Influence—The longer a person lives, particularly in high end social positions, the most they influence and direct society. This can cause the same effects as governance. For example, Yoda spent 800 years on the Jedi Council and training Jedi, which means he exerted a massive influence on the Jedi Order’s philosophy, training methods, and membership as well as exerting influence on the direction of the Republic.