The idea that the more a certain thing is used the faster it will wear out, is very old. In 350 BC Aristotle first proposed this idea could be applied to humans as well. Although the idea of aging being a result of the body wearing out did not become a popular idea until the late 1800s. Further exploring this idea in1908, Rubner published research comparing the energy metabolism and lifespans of guinea pigs, cats, dogs, cows, horses, and humans. His research showed that the rate of metabolism was within a factor of 1.5 per gram per lifespan, despite there being a 50,000 times increase in body mass between the smallest and largest species. Rubner’s research showed that a gram of body tissue has similar energy expenditure no matter the species of animal. This discovery led to the creation of the rate of living theory. The rate of living theory states that using energy faster will lead to death sooner. In the 1950’s another theory tried to explain why we age. The free-radical damage theory states that highly reactive chemicals in the body degrade biological macromolecules and cause tissue damage. These free radicals include products of radiation exposure but are most commonly thought to be products of oxidative phosphorylation. The rate of living theory has taken a back seat to the free-radical damage theory because research has shown that birds do not conform to the same energy expenditure observations that were made for mammals. There is a significant amount of contradictory research that both supports and doesn’t support these hypotheses. For example, under some conditions mitochondria can make less free radical species at a higher metabolic rate. More research needs to be done in order to further understand the links between body size, metabolism, and lifespan (Speakman 2005).
Metabolic processes provide the energy needed for all biological activity. Metabolism is affected by many different factors, for example body size. Respiratory metabolic rate (R) is related to body (M) described by the function R=aMb (a = normalization constant and b = scaling exponent). ¾ is the value generally used for b. But, the generalization of ¾ for the scaling exponent has been shown not to be true under different taxa and has flaws. MLB is a hypothesis used to fix the ¾ generalization for the scaling exponent. MLB states that the scaling exponent should be between 2/3 and 1 to account for the different metabolic rates of different organisms and conditions (Glazier 2008).
The main purpose of these experiments is to demonstrate the relationship between BMR and body mass in mammals and birds. Additionally, it is investigated whether or not reptiles have a BMR than mammals and birds since they are ectothermic. This was done using data collected from the Quadvark database.