Which creature came first, jellies or sponges? For almost 100 years, biologists assumed sponges were the first animals to evolve because they were such simple organisms.
Sponges don't have circulatory, nervous or digestive systems. To survive, water must continuously flow through their porous bodies.
Unfortunately for SpongeBob, and all sponges like him, one recent study has come down definitively on the side of the jellies — comb jellies, to be exact.
Comb jellies might look like jellyfish, but they're actually a distinct group of animals.
Long story short, scientists looked at a bunch of genes all organisms shared, tallied which ones were most closely related to similar genes in sponges or jellies, and declared jellies the winner.
The scientists say their method can be used to solve many genetic controversies. In fact, the researchers also found that crocodiles are more closely related to turtles than to birds. But the researchers say sometimes, evolution happens so quickly that not enough genetic evidence is left behind to determine which species came first or which are more closely related.
But, as with many things in science, nothing is that clear-cut. Just last month a huge study was released in favor of the "sponges came first" theory. So this probably isn't the final nail in this debate's coffin.