what percentage of Americans are naturally red-haired?
The stat I’ve heard is 1 in 20 (thus 5%).
The other stat I’ve never managed to forget is that 1 in 88 births yields twins.
Not enough. 
For some reason I was expecting a lightbulb joke, until I realized which forum I was in.
But let me just echo Neidhart’s sentiment. [homer]redheads…mmmm[/homer]
[hijack]
My wife’s got very red hair. I have brown hair. No one in my family, that I’m aware of, has red hair. My sister-in-law has reddish highlights, and there’s a redhead or two a couple of generations back in her family.
What are the chances of our child being a redhead?
[/hijack]
(My wife would agree with the “not enough” comment.)
depends how many kids you have.