Azawakh follow Allen’s and Bergmann’s Rules

December 4, 2008


In 1887, Joel Asaph Allen posited a biological rule that warm-blooded animals in colder climates tend to have shorter limbs than the equivalent animals from hotter climates. Christian Bergmann, posited a similar rule in 1847. Bergmann’s rule is that the body mass of warm-blooded animals increases in colder climates.

Azelouan 110 degrees Farenheight

Azelouan 110 degrees Fahrenheit

The mechanism behind these phenomena is thought to be temperature regulation. Warm-blooded animals have to maintain a narrow core body temperature range or they die. Surface area to volume ratio is a critical factor in heat transfer. A low surface area to volume ratio tends to retain heat while a high one tends to radiate heat into the environment. This effect is the reason that car radiators and the heat exchanger in an airconditioner have huge surface area.

Surface and Volume

Shape controls the ratio of surface area to volume. A sphere is the shape with the minimum surface area for volume while a flattened pancake has close to the maximum surface area for volume. This is oranges burst when you squeeze them. As the orange flattens, its volume stays constant but the skin must stretch. Eventually you exceed the elasticity of the skin and the orange bursts.

Another example is a stack of 8 sugar cubes (1cm x 1cm x 1 cm). If you stack the cubes 2 x 2 x 2, then the volume is 8 cubic cm and the total surface area is 16 square cm. If you stack the cubes in a 1 x 2 x 4, then the volume is still 8 cubic cm but the total surface area is 22 square cm.

Azawakh Morphology

Azawakh are medium-sized hounds in the range of 40-50 pounds. That makes them the same mass as a Norwegian Elkhound but about 7 inches taller. That’s Allen’s rule in play. An English Greyhound is of roughly similar height to an Azawakh but weighs 20-30% more. This is Bergmann’s rule in play.

To use a car metaphor, the Elkhound has the same size engine but a much smaller cooling system and the Greyhound has the same cooling system but a much larger engine. The flat, dry musculature, long legs and high tuck of the Azawakh are all adaptations for heat tolerance.


9 Responses to “Azawakh follow Allen’s and Bergmann’s Rules”

  1. Brett Says:

    Normally I would agree, but then by this same reasoning Lions would almost look like camels and this clearly isn’t the case. It works better for colder climates that hot ones. Because the Azawakh/Sloughi types, the Saluki/Afghan types and then the regular Greyhound types are all results of convergent evolution (or more likely being breed for the same trait) and are actually not related it would seem that speed is the reason the legs are so long.

    It’s interesting that while not really related, they all have the same double suspension gallop:)



  2. Brian Reiter Says:

    You have struck upon the reason that it is called Allen’s “Rule” and not Allen’s “Law”. It’s more of a rule-of-thumb. It works less well for comparisons between species and there are lots of other selection factors besides heat. Lions are quite a bit different from dogs. One thing that is very different is that while the females will hunt, they usually hunt after dark or at least in the evening when it is not so hhot. They also acquire a lot of meat by stealing kills from Wild Dogs and Hyenas.

    The usual example of a species that breaks Bergmann’s Rule is African Elephants, which are huge. One could argue that Pleistocene Mastodons were even larger (and northern saber-tooth cats were larger than lions) but that’s really cheating, isn’t it?

    The basic body plan for an undifferentiated wild dog or wolf is that of a cursorial hunter. In that respect a double suspension gallop is a “primitive” or ancestral trait. It’s less amazing to me that the Celtic, Mediterranean, Asian, Arabian and African coursing hounds have a double-suspension gallop capability than that selective breeding has removed such a basic feature from so many other breeds of dog.

  3. Brett Says:

    The elephant in Africa has larger ears then the Asian variaty. These are specific adaptions for the heat, basically larger surface area for cooling. Remember that the temperatures were cooler during the ‘ice age’.

    These dogs follow the form follows function rule. look at the cheetah and leopard. The cheetah runs it prey down over a distance while the leopard is an ambush predator. And while it is a rule and not a law, the point is they DON’T follow this rule. At first glance it sound good, but in reality it’s not the case. Greyhounds are a relatively young breed but they are favored and possibly even created in Europe, its not very hot there so by this rule they should have shorter legs. They don’t. Plus your arguing natural evolution for a created breed. Once humans took over breeding natural evolutionary laws go out the window.

    And the SOUTHER saber toothed cats were the big ones. The others were lion sized or smaller.

    The wild dog are another example of form follows function, they are only very distantly related to domesticated dogs.



  4. Brian Reiter Says:

    A greyhound is a much larger animal than an Azawakh. It masses about 30% more, yet stands around the same height. Relative to it’s mass, it’s legs are shorter. The greyhound also has much less surface area for the amount of heat-producing mass. All of this means that the greyhound is much less heat tolerant than the Azawaakh. I’m told that you have to be careful coursing a greyhound in heat over 70 degrees Farenheight whereas you can run a fit Azawakh in heat over 100 degrees Farenheight.

    It’s true that I am arguing that natural selection plays a much larger role in the development of domestic animals in the Sahel than in Europe. The Sahel environment is much more strenuous and animals that can’t handle it die.

  5. Brett Says:

    You’re arguing against the facts. What about the other colder climate sighthounds like the mountain type Afghan, the Taigan and the Tazi? All can be found in colder climates but all have long legs. You’ve fallen into the trap that the Azawakh are something special or their is something extra special about them that other breeds like them don’t have. You can also run a saluki at those temps for miles. Does that also mean the saluki’s legs are for temperature regulation. You could argue the leg ‘flap’ that asawakh have is for temperature regulation, I’ll by that, but not their long legs when so many other breeds in all sorts of climates have them (as do wolves and the manned wolf, moose and if you want to go this far, Jaguars have shorter legs the closer you get to the equator.)

    They are a fascinating animal with a somewhat uniques history, but they are a man made breed, made specifically for running. THAT is why they have long legs, and to really hit this home, the ones in Africa or from Africa have shorter legs than what you traditionally see in the states or the US. We have breed them to be even more extreme, as that is what the show people prefer.



  6. Brian Reiter Says:

    I’m not sure that we’re talking about the same things. I didn’t say anything about Saluki or that Azawakh are uniquely adapted, just that they are adapted differently than a greyhound. If you were to take an English greyhound to the Sahel (or Saudi Arabia) and try to run it on hare or Oribi or Thomson’s gazelles, it would die of heatstroke.

    Saluki and Azawakh have very similar heat adaptations, especially if you look at samples from intensly hot places like the Arabian desert. Are you arguing that there are exceptions to Allen’s Rule or are you arguing that volume to surface area ratio is irrelevant to thermal regulation?

  7. Brett Says:

    I’m arguing that the long legs in sight hounds have nothing to do with heat regulation but with running down prey, you’re telling me the opposite. I pointed out that other sight hounds in colder climates also have long legs and thus Allen’s and Bergmann’s Rules do not apply in this case. Also, the Sahara has only been a desert for the last 6,000 years, while Azawakh have been around as a breed for 10,000 (DNA evidence.) So the long legs were around before the high heat. Long legs are NOT adaptations in this case, compressed feet, black skin pigment ect, ARE adaptations for heat, but since humans have controlled breeding these can’t be called natural adaptations.

    I would say that the leg flap (from leg to body, the name escapes me) which is larger than other sight hounds would be used for thermal regulations.

    As I originally said Allen’s and Bergmann’s Rules are great for cold climate adaptations and sometimes don’t apply for hot weather as some animals will switch to a nocturnal lifestyle instead of making radical body modifications to escape the heat. (Jess pointed out that neither the Azawakh or Saluki are run in 100 degree heat, they usually hunt them in the early morning or evening or in the winter.)



  8. Brian Reiter Says:

    Hi Brett,

    We don’t have to agree about whether Allen’s rule applies to Azawakh. I don’t think we are going to convince each other, but that’s OK.



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