Darwin, Then and Now

Darwin theorized natural selection to act through “slight, successive” changes -

“I do believe that natural selection will generally act very slowly, only over long periods of time…. natural selection acts slowly by accumulating slight, successive, favorable variations, it can produce no great or sudden modifications; it can act only by short and slow steps.”                                                            

While speculation on metabolic rates was beyond the scope of nineteenth century scientists, investigation in this field is now yielding new information on potential evolutionary correlates. During evolution, the continued increase in size and complexity, for example from “mouse-to-elephant”, was expected to follow corresponding “slight, successive” changes in basal metabolic rates in relationship to body mass.

The scientific team at The University of Birmingham in the United Kingdom headed by Craig White noted that the evolutionary “relationship between the basal metabolic rate (BMR) and body mass (M) of mammals has been at issue for almost seven decades.” BMR is a calculated number based on the equation BMR = aM^b and the exponent b has long been disputed. The universality of exponent b is at the center of investigation.

To determine the exponent b, the researchers studied high-quality BMR data from 585 species and a subset of 537 species and published their findings in the October 2009 edition of Evolution* entitled “Phylogenetically informed analysis of the allometry of Mammalian Basal metabolic rate supports neither geometric nor quarter-power scaling”. The team results re-establish the fact that no evolutionary relationship exists between BMR and M concluding –

“Thus, we conclude that no single value of b adequately characterizes the allometric relationship between body mass and BMR.”

Sherman J Sutter, writing for Science in the abstract entitled “Evolution: No b to Rule Them All”, concluded that -

“Their results reinforce doubts as to the existence of a universal allometric relationship between mammalian BMR and body mass.”

Evidence for the natural law of evolution through “slight, successive” changes in the BMR, as expected from Darwin’s theory of natural selection simply does not exist. Species are unique—“kind after kind.”

Evolution. 2009 Oct;63(10):2658-67.