Let’s say you have a population of 100,000. Everybody has two kids, so the population is stable. The average age of the mother at the time of giving birth is 20 years. I’m thinking what a prehistoric population would have been like.
A woman gets a mutation. How long until nearly the entire population is decended from her and thus has a chance to get the mutation, assuming people are intermarrying among the whole population? By my math, it would take at least 330 years but definitely not more than 400 years. The woman would have 2 descendants in 20 years and 4 in 40 years and 8 in 60 years and so on. After 340 years, she would have 130,036 descendants. That’s more than the total population, so we would have to assume relatives marrying each other, but she would still likely have nearly all the population as her descendants.
In reality, if the gene were favorable to survival, and people had significantly more than 2 children in the family, it could happen a lot quicker.
In a 6,000 year period, genes can spread out pretty widely.
“Let’s say you have a population of 100,000...”
2 problems with this:
a. All the other women are having children too, and unless the “blonde” woman is a serious racist and her offspring are, too, they are all intermarrying with dark skinned people.
b. Light skin coloration is a recessive (non-dominant) gene. So the chances of the woman’s offspring being light skinned, short of cloning, are pretty low.