Comb jellies such as Mnemiopsis leidyi have a through-gut, challenging when this evolutionary innovation arose.
Photo by William E. Browne, Science Magazine

Don’t minimize the importance of poop (shit to be more explicit), and don’t mistakenly think that calling someone an asshole is necessarily an insult anymore. And, once again, you can thank a variety of jellyfish – a comb jelly – for this enlightenment.

Amy Maxmen reports in the latest issue of Science magazine that these beautiful creatures don’t defecate by vomiting, as always believed, but have specialized holes at the end of their digestive tract for eliminating waste. They eat with their mouth, and eliminate at the other end through these newly discovered holes. How about that? What was “common knowledge,” namely, that an anus making a separate pathway for elimination was a critical advance for evolving species, wasn’t quite right. It goes further than that: this raises the question whether an anus developed only once in evolution and then diverged, as previously believed, or whether functional anus-like structures developed multiple times independently during evolution.

This is the same question that I and other scientists studying eye evolution struggled with for years. So, you see, even scientists can have their heads up their ass, intellectually that is.