Originally posted by s2000raj
"Another useful tidbit is the history of the missionary position. Nineteenth century missionaries proclaimed that the only natural position for men and women to have sex was with the man on top. Other sexual positions were considered animalistic and were frowned upon by religious groups. Don't get me wrong though, the missionary position is still quite popular as it allows for creative movements and deep penetration. A woman could easily wrap her legs around her partner or even hike them over her partner's shoulders for deeper thrusting. Also, this position is the easiest for a woman to stimulate her clitoris manually. The missionary position is not used by any other species of animals except other primates, such as chimpanzees. It encourages eye-to-eye contact between the partners, which humans and primates enjoy for added intimacy. "

From this interesting article that has some NSFW words in it, but is from a public source.
http://www.dailycal.org/article.php?id=3004