Earlier this year, I did a round-up on what I thought could conceivably be a biological explanation for vampires. I think such thought experiments are neat. I'm going to make you endure another.
This past week in my seminar course, we talked about this worm that has no digestive tract, no mouth, and no anus. It obtains all of its metabolic needs from bacteria which live just under its skin. The worm absorbs minor nutrients from the environment, mainly dissolved gases, and the bacteria use them to create metabolites which they share between themselves as well as with the worm. Sometimes the worm directly absorbs the bacteria for fuel as well. The worm's waste products are absorbed by the bacteria for fuel as well.
I find this to be fascinating, and we spent a good while wondering how situation would evolve. Since we were all molecular biologists, nobody had an answer. Still, I was left with one intriguing question:
What if people had turned out like this?
Think about it . . . no digestive tract at all, coming or going. What would this mean?
For starters, any joke using the punchline, "Wrecked 'im? It nearly killed 'im!" would never be known. Uranus would no longer be a funny planet name. No one could make fun of Preparation H or use "stomach problems" as an excuse to get out of work.
On a more serious note, many things would be radically different about people. You wouldn't have obesity, as all of our energy would be self-sustaining. Consequently, you wouldn't really have body-builders, either, as you couldn't get the additional energy that would need. Agriculture would never have developed, nor would hunting. What would have been the premise for the beginning of human civilization?
Of course, though we would have no mouths, we'd have to breathe a lot more, as those bacteria need the CO2 to build sugars with. Perhaps many more nostrils? Of course, with no mouth and no tongue, this leaves open the question of how communication develops. Perhaps vocal cords still exist in whatever airways we'd use, so there would still be some form of vocal communication, but it wouldn't resemble anything we call language.
And, well, reproduction is a whole other case entirely. Without a waste tract coexisting with the reproductive parts, would those parts have turned out the same? Or would they be entirely different as well?
Go ahead and add in your $0.02. I'm curious what the thoughts are on this one.