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I've heard that camels lived in the North America formerly and just in the last few thousands years they've migrated to the hot deserts. Thus they allegedly utilized the adaptations against the cold weather in the tropics.

One of this adaptations have been their humps. Clearly, it is useful not to have a thick fat layer all over your body in the hot weather. (I see it like a neural spine sail (which helps with thermoregulation to the desert fauna).) But how about the polar areas? All the other polar animals don't see to be restricted by the fact they save all the fat under their skin in any way.

So what were the original reason for the evolution of the camels' humps?

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  • $\begingroup$ Do you have a reference for "Clearly, it is useful not to have a thick fat layer all over your body in the hot weather."? $\endgroup$
    – kmm
    May 18, 2016 at 19:15
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    $\begingroup$ @kmm I suppose so, since nomads don't wear fury coats, but I think I don't really catch the whole concept, so there is probably a different reason. $\endgroup$
    – Probably
    May 18, 2016 at 19:24

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In my opinion there might be two reasons why the camel hump (rather than bump) might be one of the adequate adaptations of camels to living in the cold (additional to their flat feet giving hold on both snow and sand and tooth structure, Rybczynski et al., 2012). Both match the humps being fat storages in modern camels.

The first is also provided by Rybczynski et al. (2012):

Their iconic hump(s), containing fat, also may have been adaptive. As seen in high-latitude ungulates today (Parker et al., 2009), fat deposits could have been critically important for allowing populations to survive and reproduce in harsh climates characterized by 6-month long, cold, winters.

Note that this refers to the nutritional value of the fat deposits and does not necessarily relate to maintaining body temperature.

The difference to modern camels would be that the fat storage in modern-day camels serves indirect water deposition (water can be easily gained from the fat stored in the humps and storing the water condensed in fat molecules is way more efficient than storing water directly). This relates to the second reason which, however, is more speculative from my part.

Cold - especially in plants - also implies drought as frozen water is not available. This does not need to apply to mammals as they can thaw ice, e.g. by licking. However, this might be critical as the body might lose some temperature during that process. Accordingly, fat storage might already then have been a means to storing water while keeping body temperature.

Alternatively, and maybe even more likely, the camel hump might have undergone a switch in function from storing a food source in archaic camels to storing water in modern camels as both can be achieved with fat deposits due to the chemical properties of fat.

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  • $\begingroup$ Beat me to it by seconds! Was even going to use the same reference. Well played, sir... :-) $\endgroup$
    – Forest
    Jun 14, 2016 at 19:22
  • $\begingroup$ Is there actually a good support for the hypothesis that many of the particular camel features have evolved in a cold environment or is it still just a good hypothesis? $\endgroup$
    – Remi.b
    Jun 14, 2016 at 22:06
  • $\begingroup$ @AlexDeLarge Ok, I have heard about the water acquisition by decomposing the fats. But about the first reason: Surely, fat is used as a nutritional storage in all mamalls but what is the advantage of storing it into a single place? Other polar animals play the opposite strategy. $\endgroup$
    – Probably
    Jun 15, 2016 at 7:59
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    $\begingroup$ @Remi.b: I am not a camel expert but as far as I know the paper cited in my answer (and some fossil record papers) is pretty much what is out there. The evidence that ancestors of modern camels evolved in arctic areas seems to be strong. What traits actually evolved in response to cold does not seem to be clear. $\endgroup$
    – AlexDeLarge
    Jun 15, 2016 at 8:47
  • $\begingroup$ @Probably: I don't know. Might be that there is absolutely none. In cases like this, I often think that the contingency of evolution is the most plausible explanation. There is, however, one thing I could think of (again, speculative). According to the cited paper, camels evolved during a warm period - eventually indicating that there were harsh, cold winters but mild summers. Unlike in todays 'always cold'-arctic where a layer of fat is nice, this could have been disadvantageous in the warmer summers compared to a condensed storing in the humps. $\endgroup$
    – AlexDeLarge
    Jun 15, 2016 at 8:54

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