missionarius explicatus

 
Missionarius (a missione) est sodalis cuiusdam religionis qui ceteros religionis aliae convertere ad propriam temptaret. Usus missionariorum saepe conectitur Christianitati, sed vero et discipuli Buddhismi theoriam missionaricam invenerunt.

To be in line with history, this post should continue in Latin, the language most used for sexual matters not intended for everybody's ears. However, our three sources being English, we'll restrict ourselves to a simple  

horresco referens. 

At the risk of disappointing you, we start with a purely etymological question: where, when and how did the term missionary position originate?

Missionary in vertical position

The answer is to found in Sexual Behavior in the Human Male by Kinsey e.a. (1948, relevant pages here). 

Most persons will be surprised to learn that positions in intercourse are as much a product of human cultures as languages and clothing, and that the common English-American position is rare in some other cultures. (...) It will be recalled that Malinowski (1929) records the nearly universal use of a totally different position among the Trobrianders in the Southwestern Pacific; and that he notes that caricatures of the English-American position are performed around the communal campfires, to the great amusement of the natives who refer to the position as the "missionary position". (p.373)

Now Malinowski's The Sexual Life of Savages in North-Western Melanasia (1929) can be consulted online. (Relevant pages here.) The word "missionary" occurs seven times, but not in the section The act of Sex (pp.335-343). We do find contempt of the natives for the "missionary fashion" of holding hands and leaning against each other, called "one of the novel immoralities introduced by Christianity" (p.479). Also, it is recorded that it is one of the special accomplishments of native cook-boys and servants (...) to imitate the copulatory methods of their masters, a certain Gomaya being perhaps the best actor in this respect.

So it would appear that Kinsey concocted a condensed quote out of these several strands, adding campfire performances as couleur locale. The exotic information may have been Malinowski's, but it was Kinsey who coined the "missionary position". Anyhow, it's a contemptuous description by the Melanesian natives of a white man's ridicule and clumsiness.

One year after Kinsey and two decades after Malinowski, the Anglican Church also published on Melanesian missionaries. We refer to it for additional information on the subject.

Now that the term has been explained, let's dig somewhat deeper. White Christians settling among savages and caught in their weird practice had their excuses ready: M/F=incubus/succuba was the only theologically approved way. After all, God created man to be dominant/active and woman to be submissive/inactive! (Sort of argument to be found in Ephesians 5:23.) Also, reproduction being the first and only goal of these activities, it's only appropriate that man should be seen plowing the fertile soil. Hence all theologians since Saint Paul agree: situs naturalis est, ut mulier sit succuba et vir incubus. Dieu le veut! Everything else is situs innaturalis, by which the almighty Creator of The Universe is cosmically displeased. These unspeakable acrobatics lead straight into hell, you be warned. Apparently, Melanesia is not "naturalis" and—strangely enough—neither are our fellow mammals; if you do as they do (a tergo, modo pecunum) you're singled out for doom.

Those eager for more theology can consult 

James A. Brundage, Let me count the ways: canonists and theologians contemplate coital positions, Journal of Medieval History 10 (1984), 81-93. (here)

Theology counts as the biggest waste of intellectual energy in western history, and peeking into people's bedrooms is just one example to prove it. After all, what came of it? Today there is hardly a movie in which a man and a woman are not seen involved in non-theological bedroom activities. Next time, pay some attention, and take notes. Most of the time you will not see a plowing man but a riding woman. In this Canadian Ph.D. thesis I learnt that the Latin for the latter is equus eroticus. But doesn't one image tell more than a thousand words? Here they come. We leave it you to fill in the Latin captions.

Added 25 September 2021.  Adelbert von Chamisso travelled around the world in 1815-1818, and provides us with some extra information concerning the liberal attitudes prevailing on the Pacific Islands, more specifically Pelli Island in the Carolines. (Read the German text in Latin font here: Die Carolinen-Inseln. Should you prefer the original with the footnotes, download it here. The pages relevant for our subject are 165, 177, 180-181.) About the inhabitants, devoid of any form of shame, we learn the following:

1. Men and women are completely naked. (In former times, men on the Mariana Islands also used to be naked, but in Chamisso's days Pelli island seemed the only one left with this tradition.)
2. They copulate before everyone's eyes like animals would. 
3. Women have also sex when pregnant, but a chief designates a man of his choice to act on his behalf. (A man may have several wifes, but in other islands these have no intercourse with other men.) 
4. Marriage and divorce are entirely trivial matters. 

Some challenge for a Christian missionary!