The restaurant had a wide variety of dishes
The restaurant offered an extensive selection of dishes. sexual tapeworms have even evolved a kind of kamikaze butt the rear end of the tapeworm will detach and stay in the host’s gut and grow a new head and tail so it can reproduce and then the new tapeworms will break free and start the cycle over again
After you watch this SciShow compilation, you can find more butt facts on the SciShow Tangents podcast. It’s available on all podcast platforms.
You’ve had a butt your whole life, but you still might not be using it right. I know your butt might seem intuitive because, I mean, it comes free and ready to use—no assembly required—but there are multiple ways to do all of the things that a butt does, and some are better than others. So, I’m bringing you the user guide for your butt.
If you’re watching this video, you probably have a butt. But why? If the only reason were to empty your bowels, there wouldn’t be animals that can do that without butts. And there are so many weird and wonderful butts in the world. Olivia will talk about those guys, and then Michael will fill in why human evolution didn’t bypass the butt.
As weird and wacky as our fellow animals get, there’s one thing that we pretty much all have in common: we have to eat. And if you have to eat, you also have to release waste. Many animals share a very useful, very familiar feature: a butt—technically an anus—but the word butt is hilarious. While the function of that rear exit is pretty straightforward, the evolution of butts is surprisingly complicated and confusing.
When you get right down to it, many of us animals are basically tubes with an opening at either end: a mouth for taking in food, and an anus for releasing the unwanted byproducts of digestion. This two-ended tube arrangement is called an alimentary canal or a “through gut,” and it’s common among animals that belong to the vast group of bilateria. This includes most animals that are symmetrical down the middle, such as worms, spiders, fish, and humans.
But not all animals work this way. Sponges, for example, have no true mouth, gut, or anus at all. They absorb food particles from the water directly into the cells of their bodies. Jellyfish and anemones, on the other hand, have a functioning mouth and anus—but they’re the same opening: a “mouth-butt.” In these animals, the mouth leads directly into a sack-like gut, and then waste is spit back out when digestion is done.
But there are some serious benefits to having a through gut like we do. For one thing, the alimentary canal can develop into specialized regions to serve different purposes. Your alimentary canal, for example, includes several organs with specific functions. Your stomach’s job is to start breaking your food down into a liquidy mess, and your large intestine reabsorbs fluids and prepares waste for expulsion. The whole process is helped along by other organs like the liver and the pancreas.
The through gut can also be expanded and adjusted to fit bodies of all shapes and sizes, from worms to whales. Just imagine a blue whale with a “mouth-butt”! Its meal would have to make a ridiculous round trip to drop off nutrients and then come back out. And very importantly, animals with a through gut can carry more than one meal at a time. An anemone with a sac gut has to finish digesting and relieving itself before it can take in new food, but you can happily eat your dinner while lunch is still working its way along.
Scientists suspect that the familiar through gut and anus first evolved in the earliest bilaterian animals, and were later inherited by their descendants, like us. But trying to pin down exactly when and how the true anus has evolved is tricky. Since the evolution of butts has been a bit wacky.
For example, you’ll find a separate mouth and anus in starfish and sea urchins, but their close cousins, the brittle stars, have lost their anuses somewhere along the way. They’ve independently evolved a sac-like gut like in an anemone, using their mouth for both input and output. Most flatworms have similarly lost their anuses, but one group in particular—the tapeworms—have gone even further and lost their entire digestive tract. No gut, no butt. These parasites don’t digest their own food. Instead, they sit inside their host’s alimentary canal and absorb all the pre-digested food around them. And then some.
Some asexual tapeworms have even evolved a kind of kamikaze butt: the rear end of the tapeworm will detach and stay in the host’s