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Allen's rule
The principle holding that in a warm-blooded animal species having distinct geographic populations, the limbs, ears, and other appendages of the animals living in cold climates tend to be shorter than in animals of the same species living in warm climates. Shorter and more compact body parts have less surface area than elongated ones and thus radiate less body heat. Allen's rule is named for the American zoologist Joel Allen (1838–1921).
Compare Bergmann's rule
Example Sentences
Known as Allen's rule, it holds that, generally speaking, animals' appendages evolve to increase in size as the temperature around them also increases.
According to a recent paper published in the journal "Trends in Ecology & Evolution," Allen's rule is manifesting itself in a number of animals because of climate change.
"Allen's rule is concerned with the size of appendages – so we're expecting that the size of ears, tails, beaks, and legs will increase in size, relative to the rest of the body, as temperatures increase," Sara Marie Karin Ryding, a faculty member at the University of Deakin's Centre for Integrative Ecology, told Salon by email.
This particular manifestation of Allen's rule also speaks to the way that climate change threatens biodiversity.
The theory, known as Allen’s rule, has long appeared in biology books, but scientific evidence for it has remained weak.
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