The rate of living theory postulates that the faster an organism’s

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

, the shorter its lifespan. The theory was originally created by

Max Rubner Max Rubner (2 June 1854, Munich27 April 1932, Berlin) was a German physiologist and hygienist. Academic career He studied at the University of Munich and worked as an assistant under Adolf von Baeyer and Carl von Voit (doctorate 1878). Later ...

in 1908 after his observation that larger animals outlived smaller ones, and that the larger animals had slower metabolisms. After its inception by Rubner, it was further expanded upon through the work of

Raymond Pearl Raymond Pearl (June 3, 1879 – November 17, 1940) was an American biologist, regarded as one of the founders of biogerontology. He spent most of his career at Johns Hopkins University in Baltimore. Pearl was a prolific writer of academic books, ...

. Outlined in his book, ''The Rate of Living'' published in 1928, Pearl conducted a series of experiments in drosophila and cantaloupe seeds that corroborated Rubner’s initial observation that a slowing of metabolism increased lifespan. Further strength was given to these observations by the discovery of Max Kleiber’s law in 1932. Colloquially called the “mouse-to-elephant” curve, Kleiber’s conclusion was that

basal metabolic rate Basal metabolic rate (BMR) is the rate of food energy, energy expenditure per unit time by endotherm, endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg b ...

could accurately be predicted by taking 3/4 the power of body weight. This conclusion was especially noteworthy because the inversion of its scaling exponent, between 0.2 and 0.33, was the scaling for lifespan and metabolic rate.

Mechanism

Mechanistic evidence was provided by

Denham Harman Denham Harman (February 14, 1916 – November 25, 2014) was an American medical academic who latterly served as professor emeritus at the University of Nebraska Medical Center. Harman is known as the "father of the free radical theory of aging". ...

's free radical theory of aging, created in the 1950s. This theory stated that organisms age over time due to the accumulation of damage from free radicals in the body. It also showed that metabolic processes, specifically the

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

, are prominent producers of free radicals. This provided a mechanistic link between Rubner's initial observations of decreased lifespan in conjunction with increased metabolism.

Current state of theory

Support for this theory has been bolstered by studies linking a lower

(evident with a lowered heartbeat) to increased life expectancy. This has been proposed by some to be the key to why animals like the

Giant Tortoise Giant tortoises are any of several species of various large land tortoises, which include a number of extinct species, as well as two extant species with multiple subspecies formerly common on the islands of the western Indian Ocean and on the ...

can live over 150 years. However, the ratio of resting metabolic rate to total daily

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...

expenditure can vary between 1.6 and 8.0 between species of

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s. Animals also vary in the degree of coupling between oxidative phosphorylation and ATP production, the amount of

saturated fat A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branched c ...

in mitochondrial

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...

s, the amount of

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...

, and many other factors that affect maximum life span. Furthermore, a number of species with high metabolic rate, like bats and birds, are long-lived. In a 2007 analysis it was shown that, when modern statistical methods for correcting for the effects of body size and phylogeny are employed, metabolic rate does not correlate with longevity in mammals or birds.

References

*Rubner, M. (1908). Das Problem der Lebensdauer und seiner beziehungen zum Wachstum und Ernährung. Munich: Oldenberg. *Raymond Pearl. The Rate of Living. 1928 * * * *{{cite journal , author1=Holloszy J. O. , author2=Smith E. K. , year = 1986 , title = Longevity of cold-exposed rats: A reevaluation of the "rate-of-living theory , journal = Journal of Applied Physiology , volume = 61 , issue = Suppl 2 , pages = 1656–1660 , doi=10.1152/jappl.1986.61.5.1656 , pmid=3781978 Theories of biological ageing Metabolism

Mechanism

Current state of theory

See also

References