I would like to have in my story an animal alien species with a long lifespan. By 'long' let's assume an average lifespan of 7000 (Earth) years to give a rough idea. Would be nice to give a scientific basis to justify it.
Considerations: (for brevity am going to name this lifeform 'IT')
- IT is an animal and its metabolism is active during its lifespan. So not like the 30000 years old nematode worms.
- IT was either bred or genetically engineered by another species to be a thinking machine (not necessarily a fast one). An ideal environment was setup. So no predation, no evolutionary pressure.
- other species with much shorter lifespan are tasked to provide IT's needs. Feeding, cleaning, lobe massaging... whatever.
- IT may have a slow metabolism. Does not have to be quick to either catch food or avoid predation. Does not need quick thinking.
- IT has an evolved brain. While I don't want to use the term human-like intelligence (actually it will reason in very different ways) but is certainly capable of solving complex theoretical and practical problems... in due time. It excels in deep, parallel, creative thinking.
- Size is not a constraint, it is of the correct size to be able to live so long while supporting its complex thinking.
- Reproduction is not an issue. We can assume IT can not reproduce and is instead grown in special facilities.
Question: what chemistry would justify such a long lifespan best?
What I found out so far:
Aging and lifespan are two different aspects and not all the factors are well understood. What makes beings age? What gives them a longer lifespan?
Aging is a global decline of physiological functions, leading to an increased susceptibility to diseases and ultimately death. Maximum lifespans differ up to 200-fold between mammalian species.
In a somewhat related question @Serban Tanasa replied:
Aging is a complex and barely understood process. While some animals have lifespans of centuries, others live for mere months. It is unclear why.
We know that what we call aging involves multiple cross-linked systems. Here's De Grey's breakdown of different types of aging damage from SENS:
Mutations in chromosomes Mutations in mitochondria. Intracellular Junk Extracellular Junk Cellular Loss Cell senescence Extracellular protein crosslinks
Indeed, one of the most deeply-entrenched ideas about animal lifespan is that it is closely linked to metabolic rate – or the speed of chemical reactions that break food down into energy and produce compounds needed by cells. The notion that animals undergo cumulative damage and die sooner when they work harder like machines run at full capacity probably dates back to the Industrial Revolution.
In fact, the idea that the more oxygen an animal consumes, the greater the production of free radicals that cause damage, and therefore the swifter the ageing, is now outdated. That is thanks to more detailed studies of mitochondria, the parts of cells that generate energy.
So this suggests that IT should not need to be slow in order to live a long life.
Another aspect of long living is defense against DNA damage (including cancer).
In a study published in 2013, Magalhães and colleague Yang Li compared the genomes of pairs of similar mammals with both significantly different maximum lifespans and similar lifespans. They found that genes involved in response to DNA damage and the recycling of proteins by cells had evolved more rapidly in longer-lived species.
In 2015, he went on to lead a group that sequenced the genome of the bowhead whale, revealing species-specific mutations in genes linked to DNA damage response, the regulation of cell cycles and the control of cancer.
In 2015, a team led by Joshua Schiffman, of the University of Utah, calculated that fewer than 5% of captive elephants die from cancers, compared to a cancer mortality rate of 11-25% in humans. When they looked at data from sequencing studies, they found the African elephant has 40 copies of the gene that encodes p53 – a protein that plays a key anti-cancer role, by either preventing cells with damaged DNA from dividing until repairs have been performed, or triggering them to commit suicide. Asian elephants have 30 to 40 copies. Both humans and the rock hyrax, elephants' closest living relative, have just two copies of the gene.
This paper in particular details the evidence supporting the role of anti-cancer mechanisms, DNA repair machinery, insulin/IGF1 signaling, and proteostasis in defining species lifespans.
Of course IT may not be based on DNA. Nevertheless it will have a molecule or group of molecules used for cellular replication. Thus it will have to face challenges similar to DNA based creatures.
While here is an overview of the relation between body size, energy metabolism and lifespan.
The main two theories in modern times being the rate of living theory (ROLT) and the free-radical theory (FRT) While there is no definitive proof
The free-radical theory of ageing provides a potential mechanism that links metabolism to ageing phenomena, since oxygen free radicals are formed as a by-product of oxidative phosphorylation. Despite this potential synergy in these theoretical approaches, the free-radical theory has grown in stature while the rate of living theory has fallen into disrepute.
Definition of oxidative phosphorylation:
Oxidative phosphorylation [...] is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing the chemical energy stored within [...]. In most eukaryotes, this takes place inside mitochondria. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is so pervasive because the energy of the double bond of oxygen is so much higher than the energy of the double bond in carbon dioxide or in pairs of single bonds in organic molecules observed in alternative fermentation processes such as anaerobic glycolysis.
So I wonder: this process is undoubtedly valuable for animals that are competing for survival. But maybe a lab constructed lifeform could be built on a different basis. A biochemistry that may yield lower ATP but with the advantage of a longer overall lifespan for the organism. I understand xenobiologists don't abound on SE. Am not looking for hard science though, just some plausible explanation.