Where are SNP's from?
	100 new polymorphisms per individual--most destined to die out or remain rare most present-day SNP's arise from a period after speciation but before different human populations emerged, with about 85% present in all major human populations founder population size approx 10,000 with 5,000 generations since then; survival probability about 0.005 if a SNP present in one copy at t = 0; most SNP's arose at t < 0.