why are humans the only animals to do it in the missionary position?

Others from the ape family do use the missionary position. It has to do with walking upright. Some other animals do it also like armadillos. Dolphins mate face to face if that counts.

The animal world is scary. If a predator comes along, you want to be on all fours ready to run away. Your species will go extinct otherwise.

Humans have dominated the planet....we've built cities and we no longer are fearful of being eaten mid-sex. We can procreate leisurely.

Higher comprehension of love/intimacy.

Not true. I've seen my neighbor's dogs do it missionary (no kidding).

- Jim

You should see dolphins and monkeys go at it.