Subject: Why did evolution favor eyebrows in replacement of visor-like brow ridges?

If nature selected the emergence of these hairy patches we called eyebrows in 
order to offer our eyes extra shade and keep sweat from trickling into them, 
why did it erase in the first place the supra-orbital torus or even strong 
projecting hairless brow-ridges? Is an example of evolutionary error followed 
by its correction? Is it reasonable to think that people with very sparse or 
inexistent eyebrows (and they are not rare at all) display an archaic trait? 
On the other hand, having exceptionally projecting brow-ridges seems to be 
only seen in pathological conditions such acromegaly.

Re: Why did evolution favor eyebrows in replacement of visor-like brow ridges?