Moalem's Survival Of The Sickest Practice Test

Dating a lactase persistence mutation relies on population-genetics clues rather than just present-day frequencies. The key idea is that when a beneficial allele rises rapidly in a population due to selection, it carries a long stretch of surrounding DNA with it, producing an extended haplotype and strong linkage around the mutation. Analyzing that haplotype structure and how quickly recombination has eroded it lets researchers estimate how long ago the mutation arose and when the selective sweep began. Ancient DNA adds crucial timing by providing actual samples from different eras that either carry or lack the mutation. Seeing the allele in older samples helps pin down the minimum age and shows how its frequency changed over time. Together, haplotype analysis and ancient DNA give a temporal framework for the mutation and the selection pressure acting on it, far more informative than looking at current allele frequencies alone or at enzyme activity today. Radiocarbon dating of milk residues wouldn’t date the genetic variant itself, and measuring present enzyme activity doesn’t reveal when the mutation appeared, so those approaches don’t address the timing question.