In 1981 in the USA at collection of data on the registered diseases the large number of rare diseases which development was usually connected with decrease in immunity was revealed. This unusual decrease in protective properties of an organism was called "a syndrome of the acquired immune deficiency".
The decrease in immunity reason could not be defined long, but in 1985 found a virus, infection with which in several years leads to development of AIDS. As the first patients with AIDS in the USA were found in 1978, simple calculations allow to assume that HIV infection epidemic began there at the beginning of the beginning of the 70th years. Most of researchers considers that HIV in its modern look developed on the planet no more than 100 flyings ago. And "sexual revolution" which captured the countries of the West in the late sixties, the beginning of the 70th years helped to extend to it.