Humans belong to a sub-clasification of animals called deuterostomes (or second-mouth). During embryological development there is a period where part of the tissue “folds” back into itself creating what’s called a blastopore. The blastopore, in insects (and other members of the “other” group called protostomes, or first-mouth), forms the mouth. Not so for us and other deuterostomes. Oh, no. Our blastopore develops into the anus. We come out butt first.
For discussion on such phylogenetic fun and sillyness, I stumbled across this tidbit from Greg Morrow:
So that’s it for our animal family reunion: empty bags of water, worms with heads shaped like penises, and spiny things that hurt if you step on them. And all of us talk out of our ass.