Seems to be the case that it was popularized in the 1940s and 1950s. Not sure about the tropical conditions of the South Pacific thing, it's not like adults were going out and having it done.

Dr. Spock wrote in 1989

> What I recommended to parents about circumcision in early editions of Baby and Child Care is quite different from what I recommend now. In the 1940s, I favored circumcision performed within a few days of birth for a couple of reasons. First, there was, at the time, a commonly held belief in medical circles that women married to uncircumcised men were more likely to develop cancer of the cervix. The second reason I favored routine circumcision was that if the operation were performed on a newborn, there would be no chance of a physician scaring the bejeebers out of a boy by performing the operation when he was older.

...

>In the 1940s and 1950s circumcision became quite common. By the 1960s, 90 percent of all male newborns in the United States were being circumcised as routine procedure. Ten years later, however, opinion among doctors swung away from the belief that certain groups of women developed cancer of the cervix because their husbands were uncircumcised.It was concluded that the cause was actually lack of good male hygiene - which is not as much of a problem in this country as it is in some other parts of the world. Also, by the early 1970s, more physicians - though not all - were aware of the psychological harm that could come from circumcision after infancy, and circumcision of an older child was not suggested as frequently as in the past.