The Missionary position reference article from the English Wikipedia on 24-Jul-2004
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Missionary position

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The missionary position is probably the most well-known sex position by human species. It is said that it is so called because of a story that this sex position was taught by Christian missionaries as the only "proper" sex position. (This story is apocryphal; the term originated sometime between 19451965.)

In the missionary position,

Features of the missionary position: Disadvantages of the missionary position: