How did eyebrows evolve?
I belive that eyebrows evolved to keep sweat out of our eyes. Sweat running down your forhead will generally run down your noes, through your eyebrows, or down the side of your face. Hair, as most people know, can hold a lot of moisture, which is why eyebrows are not huge, but they still absorb some of the moisture from sweat and keep that much more out of our eyes, letting us see better when sweating.
What will they look like in a million years?
This depends on many things. With our science now, we could stop human evoloution, having humans in a million years look the same and be the same as now.
We could also change the look to make the eyebrow disapear, along with many other genetic changes that are possible with technology now and what will be created in the next million years.
And who is to say that we will even be humans in a million years? We might continue to evolve and cease to be humans as we know it.
Another thing is that while a million years is a long length of time, in an evoloutionary sense, it isn't really that huge. A good deal of time, yes, like someone turning 20, but not an amount of time that any major things should happen in. However, eyebrows changing is a relatively minor thing, so who knows.