Moalem's Survival Of The Sickest Practice Test

Estimating when selection acted on lactase persistence mutations relies on genetic signals that build up around the advantageous allele over time, plus direct evidence from ancient genomes. When a lactase-persistence allele provides a fitness benefit, it increases in frequency quickly, and the surrounding DNA tends to stay tightly linked in long haplotypes because recombination hasn’t had time to break those blocks apart. Analyzing the structure and length of these haplotypes, along with estimates of the allele’s age, lets us infer how recently the selective sweep occurred and roughly when it started. Ancient DNA adds a crucial time dimension by providing genomes from different historical periods. By measuring how common the lactase-persistence allele is in samples from various eras, researchers can pinpoint when the allele first rose in frequency and track its spread through populations. This combination of haplotype information and direct temporal data from ancient genomes gives the most precise picture of the timing of selection. Other options don’t target genetic timing. Radiocarbon dating residues can date materials but not when a genetic adaptation arose; measuring current milk consumption reflects present behavior rather than historical selective events; and satellite imaging of farms tracks agricultural activity, not genetic changes.