MadSci Network: Evolution

Re: What animals have changed physically to adapt to their climate?

Date: Thu Jun 21 10:28:18 2001
Posted By: Aydin Orstan, Staff, Office of Food Additive Safety, Food and Drug Administration
Area of science: Evolution
ID: 989093232.Ev

Dear Johnny,

Bergmann's rule states that warm-blooded animals in colder climates are 
larger than their relatives in warmer climates. One reasoning behind this 
is that larger animals have relatively smaller external surface areas and 
thus, lose relatively less body heat. There are many examples of this 
rule. For example, in Europe, larger mammals, including deer, bear, wolf 
and wild boar, increase in size towards the north-east & decrease in size 
towards the south-west. (However, there are also many exceptions to this 
rule.) A corollary of Bergmann's rule is Allen's rule, which states that 
protruding body parts, such as tails, ears and bills are relatively 
shorter in the cooler parts of the range of a species than in the warmer 

These rules are briefly discussed with examples at:

In general, the shells of cold-water marine mollusks are plainer than the 
shells of tropical mollusks. The latter usually have spines, knobs and 
thick lips on their shells that seem to protect them from predation. The 
structural differences between the shells of tropical and cold-water 
marine mollusks have been attributed in part to decreased intensity of 
predation as the water temperature decreases. Also, calcium carbonate that 
the mollusks use to build their shells is more soluble at low than at high 
temperatures. Therefore, it may be more costly for cold-water mollusks to 
obtain and retain calcium carbonate. The effects of these and other 
climatic factors on the evolution of mollusk shells have been discussed by 
Geerat Vermeij in A Natural History of Shells (Princeton University Press, 

The variation in human skin colors is another example of climate induced 
changes. Humans who receive more direct and intense solar radiation (for 
example those who live in the tropical Africa and Asia) have skins 
genetically darker than those who have less solar exposure (for example, 
northern Europeans). However, the exact adaptive advantage of having more 
or less skin pigment (melanin) in relation to the intensity of solar 
radiation is not known. You can read more about this at:

I hope these ideas will be helpful.

Aydin Orstan

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