Maximum life span is in contrast with mean life span (average life span or life expectancy). Mean life span varies with susceptibility to disease, accident, suicide and homicide, whereas maximum life span is determined by "rate of aging".
Identical twins tend to die within 3 years of each other , whereas fraternal twins tend to die within 6 years . Aging theories associated with DNA include programmed aging (or programmed aging-resistance) and theories that link aging with DNA damage/mutation or DNA repair capability.
The maximum life span of most species has not been accurately determined, because the data collection has been minimal and the number of species studied in captivity (or by monitoring in the wild) has been small.
Maximum life span is usually longer for species that are larger or have effective defenses against predation, such as bird flight, tortoise shells, porcupine quills, or large primate brains. When we look at primates, of the approximately 20,000 to 25,000 genes in the human genome, it is estimated that 6% of these are different from those of a chimpanzee which has an average lifespan of only 52 years, in contrast to the human lifespan. The difference in longevity between humans and chimps could be due to as few as a hundred genes or less; however there may be other factors that shorten the life span of chimpanzees.
The differences between life span between species demonstrate the role of genetics in determining maximum life span ("rate of aging"). The records (in years) are these:
The longest-lived vertebrates have been variously described as
Invertebrate species which continue to grow as long as they live (e.g., certain clams, some coral species) can on occasion live hundreds of years:
Mammals fed anti-oxidants show up to a 30% increase in mean life span, but no increase in maximum life span. Antioxidants are most valuable for animals that are cancer-prone or subjected to radiation or chemical toxins. There are evidently homeostatic mechanisms in cells that govern the amount of allowable antioxidant activity. Many life-extensionists have dismissed the value of antioxidants simply because they have not been shown to increase maximum life span, but such a view neglects the significance of an extended mean life span.
On the other hand Michael Ristow's laboratory has recently shown that antioxidants may prevent extension of life span. Increased activity of intracellular organelles named mitochondria due to impaired metabolism of the nutritive sugar glucose extends life span of a model organism, the worm Caenorhabditis elegans. This extension occurs (completely unexpectedly) by increasing oxidative stress due to increased mitochondrial activity. Most importantly the life-extending effect of the low-sugar diet is abolished by various antioxidants, suggesting that induction of oxidative stress may be required for health and extended life expectancy. This latter process has been previously named mitohormesis or mitochondrial hormesis on a purely hypothetical basis, and suggests that increased mitochondrial activity and specifically generation of oxidative stress due to this metabolic increase exert positive biological effects ultimately promoting health. These findings fundamentally question the hypothesis of Denham Harman, and provide a mechanistic basis for the questionable use of antioxidants in humans.
Many transgenic species of mice have been created that have maximum life spans greater than that of wild-type or laboratory mice, including Ames dwarf mice, Snell dwarf mice, mice with increased mitochondrial catalase, and others.
Some biomedical gerontologists (gerontologists who search for ways to extend maximum life span) believe that biomedical molecular engineering can someday extend maximum lifespan and even bring about rejuvenation.
One such researcher is Aubrey de Grey, who calls his project to reverse the damage called aging SENS (Strategies for Engineered Negligible Senescence). Dr. de Grey has established the The Methuselah Mouse Prize to award money to researchers who can extend the maximum life span of mice.