Problem:
Quetion: how many years back must you go before any two randomly sampled humans must have a common ancestor, assuming no consanguinuity? Assume population of 6x10^9 and 20 year generation.
I think that i should use the equation ft+1=1/(2N)+(1-1/(2N))ft, but I don't really know where to go with it.
Even if this is not the right equation to use, please, please help if you have any advice or ideas. I have been stuck for hours!
Any ideas? Or better yet, pointers to places where this has already been answered?