Why don't Humans have full body hair like other Mammals?

no all mammals have hair like you describe.. look at whales for example and dolphins...

It has to do with natural selection. The genetic strains with less body hair managed to survive, because they also either lived in warm climates in which clothes weren't necessary or else they lived in cooler climates and had the brains to either make their own clothes or else use fire to keep themselves warm. If it weren't for these circumstances, these strains would have become extinct and we wouldn't be here.

there's no way to know for sure.. but it's theorized that the reason is because during a part of our evolution to what we are now.. we spent a lot of time near the water and were evolving to benefit from that... and hair just slows/weighs you down in the water... this is supported by our webbing between our fingers and toes and the fact that our heart rate lowers once we enter the water (supposedly in an attempt to conserve oxygen... lengthening the time we could stay under water) like whales and dolphins do.

My personal guess is that the disease aspects that come with hair coats - fleas, ticks, etc - were a selective pressure against hair that outweighed the benefits.  This is speculation though.  Of course, it could just be from a cut-off event, that an isolated group of less hairy humans survived some disaster that others did not.

I'm afraid the answer is evolution. Having a full set of body hair stopped being a survival trait for our species once the first caveman (or woman) started wearing fur for extra protection from the elements. It probably goes back to one of the ice ages. Once a trait stops assisting the survival of a species it then is no longer a factor in gene selection. Living organisms have a tendency to not expend energy and resources on bodily traits that don't aid in survival or sexual attraction.
HTH

evolution over so many years.

We don't need to have full bady hair because we have the enought intelligence to make our own clothes.

An adult human's body is covered with about five million hairs?the same number that an adult gorilla has. However, human hair is generally shorter and thinner than gorilla hair. You may have to look closely to see the hairs on most of your body.

Anyway, it is obviously a part of evolutional changes. All the different factors around humans could have a role in one way or the other.

To have a look, there are 3 cycles of hair growth ? growing, resting, and shedding.


In most animals these cycles change with the season, and all hairs are in the same part of the cycle at the same time. This is why animals grow a thicker coat in the fall and shed most in the spring.


Unlike most animals, in humans each hair has its own pattern of growing, resting, and shedding. Each person sheds hair and regrows hair every day. When this balance is disturbed and more hairs are shed than are regrown, alopecia or hair loss results.

With all the changes in the lifestyles of human along with all the evolution of different technologies, I believe that all had made a disturbance in the growth pattern of the hair the reason why the hair had become too short that in some became almost unapparent. Hormonal and body chemical changes as the result of external factors could have done such great change.

Climate change.  

When "humans" were first evolving, we came from jungle areas, as do chimps and gorillas.

There was a great deal more moisture in the air, and able to support the vast stretches of jungles.  

As the climate cooled and formed ice in some areas, it made other areas (Africa) dryer.  Savana landscapes began to take over.  

Jungle forests began to shrink, eventually becoming little islands of forest, no longer conected to each other, and then vanishing altogether.

The compition in these shrinking jungle forests became extreme.  Gorillas, chimps, humans, and many other ape ancestors were all competeing for dwindling resources.

Humans learned to take advantage of life on the open savanah.  Besides learning to walk upright, and talk, one of our evolutionary advantages was to loose our fur, and develop all of our sweat glands.  Those sweatglands served to keep us cool in the hot sun.  With our ancestors dark skin, and lack of fur, we were well suited for live on the open savanah.  

Animals like the big cats mostly hunt at night, when it's cooler.  They also hunt in prides, with no one animal expending so much energy they become overheated.  Hence lions get to keep their fur.

For cheetas this is a problem.  They DO expend so much energy, AND become overheated that they have to rest and pant (their way of cooling themselves) many minutes after making a kill.  Because they hunt durning the day, and often overheat themselves, they very often loose their kill to other predators.  Lions, lepoards, and hyenas move in and steal the kills from the exsausted cheetas.  Cheetas would naturally become extinct over time, even without mans intervention...they are simply not well suited, and cannot compete efficently with other predators.

Almost all the predators are pack hunters, with only one animal running for a burst of speed/time, or ambush predators (like the leopard) so they expend little energy getting hot.  Fur affords them better protection against thorn, prey animals, and fighting rivals for mates than naked skin filled with sweat glands.

The prey animals keep fur for the same reason.  Protection against the thorns, rivals,  and somewhat against predators.  Some animals, despite all their fur, are able to sweat quiet well, like zebras.  Most animals covered with fur do not have the abundant sweat glands (domestic dogs only sweat on the bottom of their feet for example).  Prey animals for the most part are just walking around eating.  They live in herds, sometimes vast herds.

They depend on the saftey of numbers to keep themselves from being eaten, or having to run very far and overheat.  That is the object of the predators...run the prey animal until it overheats, and becomes exsausted.

So it was evolution.  It just happened that it worked for us to be naked and filled with sweat gland.  There are a few other "naked" animals too, like elephants, rhino, and hippos.

If we were naked and covered with sweat glands, it allowed us to search for food in the heat of the day, when most predators were napping in the shade.  That kept us safe.  Then we could retreat to safer areas and try to keep out of the jaws and claws of predators during the cooler hours when the predators come out.

~Garnet
Homesteading/Farming over 20 years
Avid intrest/study of evolution since early childhood.