Humans Lost Body Hair: What Happened & Why?

[Monsterboy]

Humans lost body hair in order to lose heat more efficiently according to this article.
http://www.independent.co.uk/news/s...s-from-overheating-as-we-evolved-8498623.html

So , some humans moved out of Africa and into the cold regions of the northern hemisphere , why didn't they grow their body hair back?

This article gives a number of explanations as to why humans might have lost their body hair but the 'losing heat ' hypothesis appears to be most reasonable.
http://www.scientificamerican.com/article/latest-theory-human-body-hair/

 

[Evo]

The last ice age occurred very rapidly, within a decade or even just a few years. Not enough time to adjust.

Do ice ages come and go slowly or rapidly? Records show that ice ages typically develop slowly, whereas they end more abruptly. Glacials and interglacials within an ice age display this same trend.

On a shorter time scale, global temperatures fluctuate often and rapidly. Various records reveal numerous large, widespread, abrupt climate changes over the past 100,000 years. One of the more recent intriguing findings is the remarkable speed of these changes. Within the incredibly short time span (by geologic standards) of only a few decades or even a few years, global temperatures have fluctuated by as much as 15°F (8°C) or more.

For example, as Earth was emerging out of the last glacial cycle, the warming trend was interrupted 12,800 years ago when temperatures dropped dramatically in only several decades. A mere 1,300 years later, temperatures locally spiked as much as 20°F (11°C) within just several years. Sudden changes like this occurred at least 24 times during the past 100,000 years. In a relative sense, we are in a time of unusually stable temperatures today—how long will it last?

http://geology.utah.gov/map-pub/sur.../ice-ages-what-are-they-and-what-causes-them/

 

[Monsterboy]

http://humanorigins.si.edu/modern-humans-reach-europe

Humans moved to Europe little over 40,000 years ago , they had enough time to evolve white skin for vitamin D production I think ,but why not body hair? I guess natural selection did not happen based on body hair because they started using animal skin for protection very early on and hence there was no selective pressure on this aspect.

 

[jack476]

Human ancestors lost their body hair when they began to live in hotter climates as they moved out of forest ecosystems and into plains ecosystems. Dense fur became a liability when it came to keeping cool rather than a benefit. The dry heat and lack of shade on the plains made it preferable to use evaporative cooling by sweating to regulate temperature rather than to use fur and avoid the hot sun.

From there, it was carried forward by sexual selection. Facial hair in men enhances the appearance of a broad jawline, scalp hair quality is an indicator of overall health, having less body hair overall allows figure and muscle tone to be more clearly-defined, and having certain amounts of body hair in the right places signifies an optimal mix of developmental and reproductive hormones (ie that a potential mating partner would be more likely to be receptive to advances and more likely to reproduce successfully).

Basically, it wasn't due to migrations to Europe or the development of agriculture, anatomically modern humans lost their body hair well before humans were behaviorally modern.