CCR5-Δ32 is a deletion mutation of a gene that has a specific impact on the function of T cells.At least one copy of CCR5-Δ32 is found in about (5-14%) of people of Northern European and in those of Northern European descent. There also is a small minority (1%) with the same mutation amongst Southern Europeans or Balkan Peninsula. It has been hypothesized that this allele was favored by natural selection during the Black Death for Northern Europeans. Prostitution in areas such as Corinth in Ancient Greece could have also infected those who partook in prostitution, as a similar virus existed which had flu-like symptoms and later continued to weaken the immune system of those infected. It was at the time not known how it was spread but the Plague of Athens or many future diseases in the Balkans could have also influenced the genetic mutations. This coalescence date is contradicted by purported evidence of CCR5-Δ32 in Bronze Age samples, at levels comparable to the modern European population. Smallpox may be another candidate for the high level of the mutation in the European population.