Because God wanted us to be this way you overscientifying it ;)

While people with low histamine ( Histapenics )
Have increased body hair.

Now histamine helps stimulate the immune system.
Northern eurpopeans / Northern asians generally have far less body hair than their related southern populations .
( Italians vs Nordics ) (Asian indians vs Chinese)

It is possible that the higher histamine may be helpful to ward off disease in the northern lands ( Although it seems most disease are far more southern in orgins )

Also Histamine increases blood flow , circulation , lowers blood pressure.

It is possible that the higher histamine levels could help northern populations withstand the cooler climates .

( Only problem ) I tend to find almost no data on histamine in ethnic groups . ( The few i have tend to have said african americans have higher histamine )
Which i find strange . . Histamine lowers body hair ( Asians , Northern Europeans ) Check

Histamine lowers blood pressure ( Asians , Northern europeans ) Check

Histamine causes obsessive compulsive disorder .( In my opinions , Asians and Northern Europeans have much more obsessive compulsive tendencies than african / southern groups )

But african americans have more asthma , allergies . ( So that is the true definition of the general traits of histamine )

But there are also multiple histamine receptors and distributions through out the body!

So perhaps asians , and whites have a alteration of histamine that influences a different end of the histamine traits .

I also tend to find almost no data on histamine levels in humans vs apes or other animals .

What i have found is .

Vitamin C defiency causes Exessive Histamine . (Vitamin C is a anti-histamine )

Also Humans are one of the few mammals which can not create our own vitamin c ..
The mammals inclue ( Apes , Guniea pigs , Fruit eating bats , Humans )

All eat alot more fruits containing alot more vitamin c than humans .

So perhaps a Vitamin C defiency has caused ( Humans to lose their hair , Through Exessive Histamine .

( northern populations would have had far less intakes than vitamin c . ( Matches the less body hair in northern populations )
Which also includes the ( Mayans vs the northern plains – eskimo indians )
The mayans are more hairy .

This seems to be a general world wide trait vs ( Northern Vs Southerns )

The only exeption seems to be the ( Hairy ainu of northern japan )
Which does not truely count!
For the ainu are thought to be a tibetian / nepalese transplant into japan ( 6 thousand ? years ago ? or so)

Best evidence of all is the sea mammals .

Sea mammals lack hair . ( They also lack vitamin c!) = Less vitamin c = More histamine = Less body hair .

Nothing in the sea really makes vitamin c . So all sea mammals have almost no existant vitamin c!

It is thought that vitamin c is needed to protect life on the surface ( Not in the seas )

Thus it is interesting that Sea Mammals + Humans are the only ones on earth to not have fur!

Since humans can not make Vitamin C out of carbohydrates ( Like most animals can ) Since we do not eat tons of fruits each day like a monkey!

It is thought we would need to obtain 1 gram of vitamin c a day to saturate our blood with vitamin c ( Like animals which create their own vitamin c make )

This theory explains why Sea Mammals have no fur . Explains why humans lack it . It also explains why the northern populations which lack Fruits in their diets also have less body hair .

The Testosteronee Theory is not true . ( African americans have higher testosterone than whites ) Yet generally have less body hair .

With this said . It is in my personal opinion . That humans began to first lose their fur from a vitamin c defiency . Than later on this was reinforced by natural selection which rewired us to perfer less fur .

Thus we became furless .

The sirenians (manatee/dugong) have a similar pattern of sparse hair. Dolphins swim so fast that waterflow turbulence is not reduced by sparse hair, so they lost all their hair. Walruses, manatees, humans swim and dive slow, sparse hair reduces their drag. Women have less body hair because they spent less time diving and more time wading in the warm shallows with the kids and beachcombing.

1. Why most hairy men seem to have chest hair but not necessarily hairy backs. Great apes don’t have chest hair but they have hair on other parts of their torso. I know chest hair is related to levels of testosterone, even though that doesn’t guarantee a man will have chest hair, he probably won’t have a hairy chest without enough of it. So why chest hair and not back hair? Maybe so a baby can cling to his chest? Or maybe the sun on his back caused him to overheat and so losing it was an advantage.

2. It seems like a lot of arguments for chest hair have to do with living in cold climates. But do chest hairs really make a man that much warmer? It doesn’t seem like it would.

My thoughts on neandertals: During the warmer periods they were probably naked, they probably swam a lot, they probably were quite hairy, maybe they had reddish -brown woolly body hair. Perhaps they group-ambushed various prey at waterside, then removed the whole pelt (say of a bear or moose) from the carcass, then smoked it, melting off any attached fat, killing the lice etc. then simply wearing that as a longsleeved outer garment during the cold months and adding some squirrel pelt mitts and grass-filled boots with twined cordgrass or tendons to keep everything tight and warm. Later simple sewing gave a better fit, cro-magnons may have brought sewing improvements to the area.