What is the Rate-of-Living Theory?
The rate of living theory originated in 1908 when a physiologist, named Max Rubner, discovered a relationship between metabolic rate, body size, and longevity. It states that living organisms possess a certain amount of a "vital substance" and when all of that substance is used up, we die. This belief is very old and today would be deemed unscientific. In todays scientific world a more plausible model for this theory is oxygen metabolism and energy. The thoery looks at the rate of energy production through respirationg by the conversion of oxygen to water.
This theory was initially developed to explain why most larger animals live longer than most smaller animals. Animals with the most rapid metabolism tend to have the shortest life spans, while animals with slower metabolic rates tend to have longer life spans. This has to do with the belief that all organisms are born with a certain amount of energy. If we use this energy slowly then our rate of aging is slowed. If the energy is consumed quickly aging is hastened. Long-lived animal species are on average bigger and spend fewer calories per gram of body mass than smaller, short-lived species. Although this is true among many species in the animal kingdom, it does not apply universally, particularily amongst mammals.
The rate of living theory is a scientific version of "live fast, die young".
Despite its intuitive concept, the rate of living theory does not by itself explain ageing but it can help explain some of the observations in the biology of ageing. It is true that a correlation between metabolic rates and rate of ageing can be found amongst some mammalian species, but still much variation is found.
One of the main flaws with the rate of living theory is that any damage that was generated by metabolism could be repaired in cells. Organisms would be able to evolve life spans that respond to environmental imperatives, partly independent of their total lifetime metabolism.
Although there are many flaws within this theory, it is a very important theory for the sole fact that it points out the importance of looking at metabolic activity when it comes to ageing. This theory may just be a smaller piece in a larger puzzle.
Copyright of Nick Beale
Cornell University, 2005