Elaborate Food Tubes

Of all the fall American holidays, Thanksgiving seems to place the most emphasis on eating. With so much food going into our mouths at this time of the year, it can be hard to ignore the need for waste to come out the other end. Some anatomical diagrams would have us believe that our food goes through us from one end to the other, as if simply going through a tube. We are of course more complex than that, but when did it all start? Not the first Thanksgiving, but when did we start the process of food going in one end and waste coming out the other? And how did we get to how we are today?

First of all, did we actually evolve from animals based mainly on this simple model, of food in one end and waste out the other? Somewhere between ancient single-celled organisms and us humans with our elaborate holiday meals is the answer. The Wikipedia article titled “Timeline of human evolution” traces human evolution from the origin of life all the way to modern man, in terms of increasingly specific animal taxons (categories of living things).[1] For our purposes, it might make sense to work backwards through the list and consider taxons that are increasingly general and/or older.

We can certainly rule out the basic tube structure originating in our modern human species of Homo sapiens, as well as other related taxonomic categories like Hominadae. In fact, we can rule out all those ancestors considered primates and even the rest of our mammal ancestors too. We can rule out the “proto-mammals” before them and everything back to our earliest vertebrate fish ancestors. We can rule out taxons still further back, to our earliest chordate ancestors.

Skipping some more, we can trace our ancestors back to early bilaterians. Members of the bilateria superphylum (a high-level taxon between class and kingdom) are basicly described by Wikipedia as a simple tube structure with a head end and a tail end.[2] I’m reasonably sure there was more to theses animals than that, presumably with some means of locomotion and protection, but the basic tube structure is definitely there. Bilateria is divided into deuterstomes and protostomes, based on how the body’s tube structure forms in the embryo. Observing that human gestation resembles the course of human evolution, I’m guessing the same holds for ancient bilaterians. Then the tube formation could possibly go back even further than bilaterians. Someone else can better pin down the timeframe, but I’m satisfied with going this far back. Fossil evidence seems to date bilaterians as early as 555 million years ago.

So now we have some idea of how old the tube structure is. Life has obviously changed a lot since 555 million years ago. How did we get how we are today? Evolution generally causes changes that are useful in some way. How are all those changes useful? There are too many changes to describe here, but some highlights can certainly be pointed out. If our earlier bilaterian ancestors were more worm-like (keep in mind these ancestors still lived in water), I could see there maybe being some advantage with back bones in chordates and more specific vertebrates. My guess is that our early fish ancestors could maybe swim more quickly and efficiently with muscles on a sturdier frame.

Land later became more appealing from an evolutionary point of view, and our tetrapod (four-limbed) ancestors were eventually able to crawl onto land and breath air.[3] Fur gave our mammal ancestors the additional advantage of being able to keep warm in the winter and maybe regulate temperature in warmer times too. Our primate ancestors eventually enjoyed opposable thumbs, making it easier to climb trees and wield materials as tools.[4] I’m guessing that using their brains helped ancestors of humans eventually develop into humans. Not that there was a goal of being human, but we humans seem to be better adapted for our modern world than our biological ancestors, judging from how many of us there are now.

So, yes, there is certainly some justification in applying a tube-like body diagram to humans. Aside from our add-ons like better brains, four limbs, and back bones, deep down we are biologically tubes that eat food. Granted we are now very elaborate food tubes. Our meals can also be very elaborate, especially holiday meals. At least at a time like Thanksgiving, we humans enjoy our food and company more than other food tubes ever have. Napkin color and turkey seasoning aside, we ourselves have come a long ways, which gives us something extra to be thankful for.

References

[1] https://en.wikipedia.org/wiki/Timeline_of_human_evolution

[2] https://en.wikipedia.org/wiki/Bilateria

[3] https://en.wikipedia.org/wiki/Tetrapod

[4] https://en.wikipedia.org/wiki/Primate