^^^True, there are some multiple births. But that supports my main point that frequency and type of sexual activity is not closely related to population. It is hard for people to separate sex from population in their minds, which is why people say silly things like "poor families in third world countries have so many kids because they don't have TV" ie, if they had anything other than sex for entertainment they would have fewer children.
If high frequency of hetero sex (absent the use of birth control) led to huge numbers of kids, prostitutes would all have ten or fifteen children each! Even the lesbians.