Rate-of-living theory

[1] 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.

[4] This provided a mechanistic link between Rubner's initial observations of decreased lifespan in conjunction with increased metabolism.

[8] However, the ratio of resting metabolic rate to total daily energy expenditure can vary between 1.6 and 8.0 between species of mammals.

[10][11] 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.

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.