Final answer:
Experimental evidence from genetic analysis shows a high frequency of the CCR5-Δ32 allele conferring HIV resistance, suggesting a historical selective pressure, while correlational evidence from ancient DNA studies investigates the allele's frequency during past epidemics like the Black Death, leading to ongoing debate about its selective history.
Step-by-step explanation:
Evidence Suggesting Correlation Between CCR5-Δ32 and Past Epidemics
The frequency of the CCR5-Δ32 allele in modern European populations has been a subject of scientific interest, particularly due to its association with resistance to HIV infection. One piece of experimental evidence is the genetic analysis conducted on more than 4,000 individuals, indicating a deletion mutation called CCR5-delta 32 that provides resistance to HIV. People homozygous for this mutation are highly resistant to HIV, and heterozygotes have partial resistance. This high frequency cannot be explained solely by the recent emergence of HIV, suggesting a historical selective pressure.
Correlational evidence involves the analysis of ancient DNA (aDNA), which aims to estimate the frequency of the CCR5-Δ32 allele in past European populations possibly affected by epidemics like smallpox or the plague. Historical references, such as the Black Death, were thought to influence the selection of this allele due to possible resistance to such diseases. However, preliminary results have shown ambiguity, leading to a debate on whether plague exposure was the selective factor for CCR5-Δ32's high frequency in Europe.
These pieces of evidence highlight the intersection of genetics, history, and epidemiology, as they may reveal how historical pandemics influenced human genetic diversity and resistance to diseases.