It's been hot out. I don't usually sweat like a fat person does but I have been lately, enough to run down in my eyes. So I was thinking and wondering how little hairs and the like can be selected by Nature.
The evolutionary hypothesis seems like this, there are groups of individuals who reproduce their little descendents to the point that there is a tension against their environment which they must fit to or die trying, so some live and some die. So I suppose that if I got some sweat or dirt in my eye and fell down a hill and died while a unibrow fellow did not then that would act as a rather vague sort of "natural selection" for the unibrow. He would be more likely to have children with unibrows or good thick eyebrows, until one day there would be a whole unibrow race. There are so many other variables and things that I can think of, yet "natural selection" is the Darwinian focus so it is best to leave it at that. Although I could probably extend the whole scenario to: The Origin of the Unibrow by Means of Natural Selection, or The Preservation of the Unibrow Race in the Struggle for Life, by Mynym.
If I was intent on being a half-wit about it I would try to make the hypothesis elastic enough to extend to the origin of all organisms, organs, life-cycles, eco-systems, human behaviors, etc.
For example, Ape-man:
In the case of eyebrows, perhaps the Ape-men lost much of their hair in a random mutation that natural selection culled from the original population for whatever reason. That is a small variation which could happen easily enough. The new hairless apes may have found a new place to live, leaving the other apes behind, they probably had to because of the lack of hair. That's pretty basic. Some people are more hairy to this day, which proves some common characteristics with apes, not to mention the fact that both apes and humans have heads and arms. In the case of the eyebrow specifically, the proto-humans that had the variation of some forehead hair may have been culled because they could live to see females to mate with, as they were less likely to get sweat or dirt in the eyes. Perhaps the unibrow is an atavistic feature of this, which is why it is now generally looked down on in modern times. That attitude about unibrows may be part and parcel of the mountains of evidence for evolution.
In the end, given the mountains of evidence it seems obvious that my original hypothesis indicates that every living thing has a common ancestor in an ancient mud puddle. And since it is a good explanation for the unibrow, it can probably explain everything else too.
If sometimes it seems that it cannot be made elastic enough, then perhaps vestigial eyespots hold some explanatory power: