Reasons to Believe

Bergmann's Rule and the Optimization of Life Designs

Bergmann's Rule asserts that the body mass of warm-blooded animals increases with latitude. The rule is named after the German biologist, Christian Bergmann, who first developed it in 1847. He reasoned that large-bodied warm-blooded animals, having smaller skin surface area to body mass ratio, would radiate less body heat per unit of mass. Thus, they would more easily keep warm in cold climates, but have difficulty staying cool in warm climates.

While Bergmann's Rule appears theoretically sound and consistent with an all-caring, all-powerful, all-wise Creator optimally creating life for its specific habitats, it has never been confirmed by comprehensive geographic observations of body-size variations. Now a team of nine British biologists has published detailed global maps of body-size variations for birds.1

These researchers conclusively "demonstrate a general pattern of larger body sizes at high latitudes."2 They also found a "strong pattern of decreasing body size with increasing species richness"3 and that median body sizes were larger on islands. High species diversity implies greater competition for limited resources, which favors animals with smaller body sizes. This explains the observed decreasing body size with increasing species richness. Likewise, the larger body sizes on islands can be explained by the observation that there is less species diversity on islands.

The objective of the British biologists was simply to test the validity of Bergmann's Rule for one class of warm-blooded animals through reasonably exhaustive field observations. However, by verifying that the rule was "remarkably accurate" and by uncovering body-size correlations the team also provided evidence for the Creator's wisdom in optimally designing each life-form to fit its earthly habitat.


  1. Valerie A. Olson et al., "Global Biogeography and Ecology of Body Size in Birds," Ecology Letters 12 (March 2009): 249-59.
  2. Valerie A. Olson et al.: 249.
  3. Ibid.

Subjects: Life Design

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. Read more about Dr. Hugh Ross.