It turns out that the coat covering mammals, can not only warm, but cool. However, it should be very rare. Scientists have found that it is for this elephants need their bristles, the density of the hairs which per square centimeter of skin is very low. These hairs are as devices for effective heat dissipation.

On the question why mammals need a coat, will be able to answer any student, not progulyatsya biology lessons. "The coat is insulating cover" - he will say, and will be absolutely right. Indeed, many millions of years ago the ancestors of mammals "acquired" wool in order to reduce the loss of body heat. And although it keeps the heat slightly worse than the feathers, but still covered her mammals not particularly suffer from hypothermia.

This evolutionary acquisition enabled once the ancient ancestors of mammals go to this teplokrovnosti. However, she constant body temperature is due to the fact that we spend on heating of the body is approximately 85-90 percent of the energy supplied to us with food. However, without external heat insulator all this would be in vain, as obtained from eating heat instantly left would our body.

However, wool, rescuing from hypothermia causes several problems in animals, living in a hot climate. And the most important one of them is overheating. Judge for yourself: the hair and so holds endogenous, that is, the internal heat of the body - and here and outside the sun was hot, so they look like they would boil in their own skin. It is especially hard to large animals like Buffalo, rhinoceros and elephant. Because, as we remember, the body almost on 90% consists of water, which cools down very slowly.

It turns out that heat of the day elephant per night even really cool not time - too much water in his body. But in the morning he again have to take sun baths. And even elephants have too small a surface of the body in relation to the volume, so that all the heat that is generated in the bowels of the giant body simply does not have time to disperse in space. It is not surprising that in order to avoid thermal shock, giant African savannas have to lie for hours in the mud, lying in the dust (which is similar sunscreens) and to drink not less than 300 litres of water a day (at least some, but still cool).

However, the elephants there are some physiological adaptations that help them to survive in such a climate, where daytime temperatures can exceed 50C. For example - a huge ears pierced network of blood vessels. It is in their blood cools faster and therefore cools and the entire body. And, of course, the coat tropical giants is very, very rare - we can say that the function of heat insulation, she no longer has.

But why coat elephants have not disappeared altogether? Zoologists from Princeton University(USA) decided to investigate this question. They are working with the African Savannah elephants (Loxodonta africana), measured as the heat radiating surface of the skin of an elephant with hair and without them. Taking into account the density of the hairs on the skin and temperature, and humidity, and even wind speed (if it exists). In the result, the researchers discovered an amazing thing - it turns out, wool not only does not prevent the elephants to allocate excess heat, but even it helps to do it!

According to their research, the heat loss from the skin, covered with hair was longer by 5-20%, depending on wind speed than with those without wool. Interestingly, the maximum heat sink was observed in those conditions, when there was no wind or he was very weak, and the humidity is very low. It turns out that the coat is really helping the giants to give extra heat to the ambient air. But how is this to happen?

Zoologists suggest that the hairs on the body elephants can work as heat instruments. They collect raising from the skin heat, then allocate it in the air. Well, since even the rare hair still greatly increase the surface area of the body, and dissipates heat more efficiently. We can say that it is rare coat and makes the ratio of the volume of the elephant to the surface so that all the excess heat is removed quickly.

Was discovered and another interesting fact. As you know, the stronger the wind blows, the better cools what he blows. Now, it turns out that at the surface of the skin, even if she was naked, the wind speed is much slower. Well, hair transfers heat much farther from the surface, to the area where the wind blows stronger, respectively, and heat is much more effective.

In addition, scientists in skin Savannah elephants found out, when the hair stops to keep warm and begins to cool the body. It turns out that this happens when the density of the hairs less than 30 per square centimeter. Well, those of elephants, this value is equal to 0.1 per square centimeter - that is much lower than needed. That is why overheating they are not afraid - no matter how heated the air around them thin coat will always work not as "insulation", and a refrigerator.

The authors believe that, apparently, elephants source, i.e. from the beginning of the emergence of both groups were redkozemelnye animals. This seems to be true - indeed, Hootie was formed in hot regions of the planet. And only after, when these giants before glacial periods settled in temperate zones, they ' overgrowing". In this way there appeared a powerful hair at Mamontov, who was not cooled, and warmed. Well, Hootie tropics remained "glabrous" - for a normal life for them was enough rare bristle...