Human variation and race

The effect of heat on our bodies varies with the relative humidity of the air.  High temperatures with high humidity make it harder to lose excess body heat.  This is due to the fact that when the moisture content of air goes up, it becomes increasingly more difficult for sweat to evaporate.  The sweat stays on our skin and we feel clammy.  As a result, we do not get the cooling effect of rapid evaporation. In dry, hot weather, humidity is low and sweat evaporates readily.  As a result, we usually feel reasonably comfortable in deserts at temperatures that are unbearable in tropical rain forests.  The higher the desert temperatures, the more significant of a cooling effect we get from evaporation.

A short term adaptation, as stated above, to this is sweating. The warm water evaporates off of your skin very quickly, bringing the heat with it.

A facilitative adaptation is to have the ability to physiologically acclimatize to hot conditions over a period of days to weeks.  The salt concentration of sweat progressively decreases while the volume of sweat increases.  Urine volume also reduces.  In addition, vasodilation of peripheral blood vessels causes flushing, or reddening, of the skin because more blood is close to the surface.  That blood brings heat from the core body areas to the surface where it can be dissipated easily into the environment by radiation.

A developmental adaptation to this is that some human nerve cells have proteins on their surfaces that enable them to differentiate between several different temperatures in the mildly warm to hot range.  This sensing ability may play an important role in the way we respond physiologically to hot temperatures. The building blocks, or subunits, of heat-sensitive ion channels can assemble in many different combinations, yielding new types of channels, each capable of detecting a different temperature. In cell cultures, this demonstrates that only four genes, each encoding one subunit type, can generate dozens of different heat-sensitive channels. Ion channels are pores in cell membranes. Their ability to open and close controls the flow of charged ions, which turns neuron signalling on or off -- in this case to inform the body of the temperature the neuron senses. It says 'I remember this temperature. I will make a really loud noise to tell the system that it is coming.'

A cultural adaptation is the turban. A turban is a piece of cloth wrapped over the head that immensely helps as a barrier between the hot sun and your skin.  Turban styles vary from region to region. The Sikh turbans are simple cloths wound round the head with a prominent front fold above the forehead. Muslim men often wrap turbans around their caps, known as kalansuwa. Afghan men often favor longer turbans that leave a tail hanging down the back. The turbans of Iran are usually black or white and wound flat and round against the top of the head. Indian turbans can be some of the most elaborate, covered with gems, jewels and embroidery. Some of the simplest turbans are those worn by African desert dwellers that swaddle the cloths about their heads and face for protection.

If you take anything away from this, it is to help you remember to keep hydrated so you can keep sweating in hot climates, and that the more you let your body be in these climates, it will be able to sustain itself easier over time and 'practice' so-to-speak.

Human race does not really have an effect on the way a human retains heat. It is some relevancy to study the effects of heat on different people close or further away from the equator, but even this is not trustworthy due to the vast variation of peoples today in different cultures. It is all the individual, so it is much more productive to study the environmental effects on humans rather than race.