{{short description|Theory of biological ageing}} [[File:Rate of living img.png|thumb|As metabolic rate increases, the lifespan of an organism is expected to decrease as a direct result. The rate at which this occurs is not fixed and thus the -45° slope in this graph is just an example and not a constant.]] The '''rate of living theory''' postulates that the faster an organism's [[metabolism]], the shorter its [[Longevity|lifespan]]. First proposed by [[Max Rubner]] in 1908, the theory was based on his observation that smaller animals had faster metabolisms and shorter lifespans compared to larger animals with slower metabolisms.<ref>Rubner, M. (1908). Das Problem det Lebensdaur und seiner beziehunger zum Wachstum und Ernarnhung. Munich: Oldenberg.</ref> The theory gained further credibility through the work of [[Raymond Pearl]], who conducted experiments on [[drosophila]] and cantaloupe seeds, which supported Rubner's initial observation. Pearl's findings were later published in his book, ''The Rate of Living'', in 1928, in which he expounded upon Rubner's theory and demonstrated a causal relationship between the slowing of metabolism and an increase in lifespan.<ref>Raymond Pearl. The Rate of Living. 1928</ref>
The theory gained additional credibility with the discovery of [[Max Kleiber's law]] in 1932. Kleiber found that an organism's [[basal metabolic rate]] could be predicted by taking 3/4 the power of the organism's body weight. This finding was noteworthy because the inversion of the scaling exponent, between 0.2 and 0.33, also demonstrated the scaling for both lifespan and metabolic rate, and was colloquially called the "mouse-to-elephant" curve.<ref>{{cite journal |author=Speakman J. R. |year=2005 |title=Body size, energy metabolism and lifespan |journal=J Exp Biol |volume=208 |issue=9 |pages=1717–1730 |doi=10.1242/jeb.01556 |pmid=15855403 |bibcode=2005JExpB.208.1717S |doi-access=free}}</ref>
==Mechanism==
Mechanistic evidence was provided by [[Denham Harman]]'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 radical]]s in the body.<ref name=":0">{{cite journal | author = Harman D | year = 1956 | title = Aging: a theory based on free radical and radiation chemistry | journal = Journal of Gerontology | volume = 11 | issue = 3| pages = 298–300 | doi = 10.1093/geronj/11.3.298 | citeseerx = 10.1.1.663.3809 | pmid = 13332224 }}</ref> It also showed that metabolic processes, specifically the [[mitochondria]], are prominent producers of free radicals.<ref name=":0" /> This provided a mechanistic link between Rubner's initial observations of decreased lifespan in conjunction with increased metabolism.{{cn|date=November 2024}}
==Current state of theory==
Support for this theory has been bolstered by studies linking a lower [[basal metabolic rate]] (evident with a lowered heartbeat) to increased life expectancy.<ref>{{Cite journal|url=http://physrev.physiology.org/content/87/4/1175.full|doi = 10.1152/physrev.00047.2006|title = Life and Death: Metabolic Rate, Membrane Composition, and Life Span of Animals|year = 2007|last1 = Hulbert|first1 = A. J.|last2 = Pamplona|first2 = Reinald|last3 = Buffenstein|first3 = Rochelle|last4 = Buttemer|first4 = W. A.|journal = Physiological Reviews|volume = 87|issue = 4|pages = 1175–1213|pmid = 17928583|url-access = subscription}}</ref><ref>{{Cite journal|url=http://www.discoverymedicine.com/S-J-Olshansky/2009/07/25/what-determines-longevity-metabolic-rate-or-stability|title=What Determines Longevity: Metabolic Rate or Stability?|journal=Discovery Medicine|date=25 July 2009|volume=5|issue=28|pages=359–362|last1=Olshansky|first1=S. J.|last2=Rattan|first2=Suresh IS|pmid=20704872}}</ref><ref>{{Cite journal|url=http://genesdev.cshlp.org/content/19/20/2399.full|doi = 10.1101/gad.1366505|title = Metabolism, ubiquinone synthesis, and longevity|year = 2005|last1 = Aguilaniu|first1 = H.|author1-link=Hugo Aguilaniu|last2 = Durieux|first2 = J.|last3 = Dillin|first3 = A.|journal = Genes & Development|volume = 19|issue = 20|pages = 2399–2406|pmid = 16230529|doi-access = free}}</ref> This has been proposed by some to be the key to why animals like the [[giant tortoise]] can live over 150 years.<ref>{{cite web |url=http://www.immortalhumans.com/the-longevity-secret-for-tortoises-is-held-in-their-low-metabolism-rate/ |title=The Longevity Secret for Tortoises Is Held In Their Low Metabolism Rate |website=www.immortalhumans.com |url-status=dead |archive-url=https://web.archive.org/web/20100720034855/http://www.immortalhumans.com/the-longevity-secret-for-tortoises-is-held-in-their-low-metabolism-rate/ |archive-date=2010-07-20}} </ref>
However, the ratio of resting metabolic rate to total daily [[energy]] expenditure can vary between 1.6 and 8.0 between species of [[mammal]]s. Animals also vary in the degree of [[Chemiosmosis|coupling between oxidative phosphorylation and ATP production]], the amount of [[saturated fat]] in mitochondrial [[Outer mitochondrial membrane|membrane]]s, the amount of [[DNA repair]], and many other factors that affect maximum life span.<ref>{{cite journal |vauthors=Speakman JR, Selman C, McLaren JS, Harper EJ | title=Living fast, dying when? The link between aging and energetics | journal=The Journal of Nutrition | volume=132 | issue=6, Supplement 2 | year=2002 | pages=1583S–1597S | url=http://jn.nutrition.org/cgi/content/full/132/6/1583S | pmid=12042467 | doi=10.1093/jn/132.6.1583S | doi-access=free }}</ref> Furthermore, a number of species with high metabolic rate, like bats and birds, are long-lived.<ref>{{cite book|last=Austad|first=Steven|title=Why We Age: What Science Is Discovering about the Body's Journey through Life|url=https://archive.org/details/whyweagewhatscie00aust|url-access=registration|year=1997|publisher=John Wiley & Sons|location=New York|isbn=9780471148036}}</ref><ref>{{Cite web|last=Timmer|first=John|date=2019-06-11|title=Why do bats have such bizarrely long lifespans?|url=https://arstechnica.com/science/2019/06/why-do-bats-have-such-bizarrely-long-lifespans/|access-date=2021-08-31|website=Ars Technica|language=en-us}}</ref> 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.<ref>{{Cite journal|vauthors=de Magalhães JP, Costa J, Church GM |title=An Analysis of the Relationship Between Metabolism, Developmental Schedules, and Longevity Using Phylogenetic Independent Contrasts |journal=The Journals of Gerontology Series A: Biological Sciences and Medical Sciences |volume=62 |issue=2 |pages=149–60 |date=1 February 2007 |pmid=17339640 |pmc=2288695 |url=http://biomed.gerontologyjournals.org/cgi/pmidlookup?view=long&pmid=17339640 |doi=10.1093/gerona/62.2.149 }}{{dead link|date=May 2016|bot=medic}}{{cbignore|bot=medic}}</ref>
==See also== * [[DNA damage theory of aging]] * [[Life history theory]] * [[Longevity quotient]]
== References ==
{{reflist}} * 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 | author = Speakman J. R. | year = 2005 | title = Body size, energy metabolism and lifespan | journal = The Journal of Experimental Biology | volume = 208 | issue = Pt 9| pages = 1717–1730 | doi = 10.1242/jeb.01556 | pmid = 15855403 | bibcode = 2005JExpB.208.1717S | doi-access = free }} * {{cite journal | author = Harman D | year = 1956 | title = Aging: a theory based on free radical and radiation chemistry | journal = Journal of Gerontology | volume = 11 | issue = 3| pages = 298–300 | doi = 10.1093/geronj/11.3.298 | citeseerx = 10.1.1.663.3809 | pmid = 13332224 }} * {{cite journal |vauthors=Speakman JR, Selman C, McLaren JS, Harper EJ | date = June 2002 | title = Living fast, dying when? The link between aging and energetics | journal = Journal of Nutrition | volume = 132 | issue = 6| pages = 1583S–97S | doi = 10.1093/jn/132.6.1583S | pmid = 12042467 | doi-access = free }} * {{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 }}
[[Category:Theories of biological ageing]] [[Category:Metabolism]]