New study ties the 'buttholes' of fish to the evolution of human fingers
It’s science! 🐟

Finally, the science we really need.
We’re all familiar with the viral obsession of cat buttholes, but after this story, fish buttholes might be the next new thing.
We already knew that digits, aka fingers, evolved from genetic programs present in fish, considering all vertebrates can be traced back to an aquatic ancestor (cue mermaid theories).
However, until now, just how digits evolved from our deep sea brethren remained a mystery. Thanks to a recent study published in Nature from research teams across the globe—including Geneva, France, Massachusetts, and Chicago—we’ve learned that they likely evolved not from fins, as many experts suspected, but from the fish’s cloaca.
Even fish can hardly believe it. media2.giphy.com
Wondering what a cloaca is? You’ve come to the right place!
For many vertebrates, including reptiles, birds, amphibians, and fish, the cloaca serves as a single opening for the digestive, urinary, and reproductive systems. Compare that to the anus, which only serves solely as waste elimination. Basically, a cloaca is a butthole, and then some! Just a little bit of anatomical distinction for context.
Researchers made this discovery by studying the embryos of mice and zebrafish, using fluorescent markers to light up which region of each species contained Hox genes, which are responsible for creating extremities. For mouse embryos, it was the digits, whereas for the zebrafish, it was the cloaca.
Below is an image the Hox gene in zebrafish of one of the zebrafish embryos from the study.
A zebrafish embryo with the cloacal region lit with Hox activity.Brent Hawkins/UNIGE
While this is just a fun bit of (very weird) trivia to throw out at parties, and perhaps gross out some fellow partygoers, it also provides a rather profound example of just how efficient nature truly is.
“The fact that these genes are involved is a striking example of how evolution innovates, recycling the old to make the new,” said Denis Duboule, honorary professor at UNIGE and the Collège de France and initiator of the study.
“Rather than building a new regulatory system for the digits, nature has repurposed an existing mechanism, initially active in the cloaca.”
It’s also an interesting depiction of how nature, as cosmic and chaotic as it appears, also tends to repeat itself in patterns.
"The common feature between the cloaca and the digits is that they represent terminal parts," wrote geneticist Aurélie Hintermann, another researcher in the study.
"Sometimes they are the end of tubes in the digestive system, sometimes the end of feet and hands, i.e., digits. Therefore, both mark the end of something."
Guess it really is true: every new beginning comes from some other beginning’s end.