Answer: When DNA is being copied for the Daughter cells
Explanation: There is a mistake when the DNA is being copied for the new daughter cells. When a cell divides, it must divide its DNA into 2 exact copies of the orginal DNA for the 2 new daughter cells. Sometimes the copy isn't correct and the cells mutates.
Basically what happened was the population went through a population bottleneck in the 1800s which then resulted in the only way for future offspring was a lot of positive assortative mating which results in fewer genetic variation(similar to the founder effect for the second part)
the inner layer of the earth
This is possible because it way more live than dead