How come that humans have long scalp hair? What biological purpose does it serve?
Why does the hair on the scalp grow so long, thick and strong? (Well, for quite some, that is.)

And why is other hair shorter?
Why is the hair on the face (cheeks, nose, forehead), ears and neck so fine and short?

Why is the hair in the armpits and the pubic area of a different quality and length?

How come that some people are "atavistically hairy", have a lot of hair on their back, or on the whole body?

I have wondered the same thing.

I remember hearing that hair is some kind of waste product.
Well, we no longer need a lot of body hair because we have clothing that keeps us warm enough. We do need some facial hair (eyelashes) to keep sweat from coming into the eyes. We need scalp hair to be attractive to mates.

Mice have 4 different types of hair that are formed during the development of the embryo in successive waves. I don't think these include the whiskers.

It is apparently normal to have different hair types. The different types are under different genetic control. Some transgenic mice develop one sort of hair but not another. I imagine there would also be some kind of spatial genetic control.

I remember hearing that hair is some kind of waste product.
Well, we no longer need a lot of body hair because we have clothing that keeps us warm enough. We do need some facial hair (eyelashes) to keep sweat from coming into the eyes. We need scalp hair to be attractive to mates.

Well in that case im glad knowing that we'll have scalp hair for a long time being.

We need scalp hair to be attractive to mates.

We don't NEED scalp hair to be attractive! It just turns out that it is for some reason.

Scalp hair has become very important since the days we became bipedal as it protects the skin from the damaing rays of the sun. This is also one of the main reasons for body hair on other mammals.

Are we wearing cloths at the cost of loosing our natural coat of hair?

many humans don't have long hair. In dry desert or savanna climates there hair is short, hum perhaps it something to do with temperature and sunlight?

Can we relate silicon element with the type of hairs. Hair seems to contain silicon.

Kumar,

are you smoking crack???

google up Alpha Keratin.

I guess one reason we have so little hair could be that we specialized in sweating as a cooling down mechanism. It is rather effective if you can 'fuel' up with water regularly.

Watch the last episode of life of mammals and see how people used to hunt in more 'primitive' style. The ran after their prey (on the hot savanah) until it collapsed from heat exhaustion. The hunter is also bordering on heat exhaustion, but has just a slight edge with his efficient sweating.

Hair

The outer shaft of hair, that provides elasticity and strength, is rich in Silicon. Hair with higher Silicon content tends to fall out less and has more shine and luster.http://www.lef.org/magazine/mag2003/apr2003_report_silicon_01.html
WellCookedFetus, Google search also mentions this.

well after further review I guess your right Kumar, sorry about that. :)

Skin, hair & nails seems to have some similarities in their constituents. Btw, If their chemical compositions is availabe anywhere?

Maybe they serve some sort of insulation when dry, and cooling mechanism when wet by sweat.

May I pose another question, how has evolution and adaption and climate changes contribute to all these different kinds of hair?

African hair generally is flat or tapelike in cross section and are likely to curl
Asian hair is mostly round in cross section
European hair is oval in cross section, has slight tendency to curl, and has a wide range of colours