We are talking about events of over 600 million years ago. Could be blurry.
From Amy Maxmen at Nature:
For the better part of the past century, zoologists arranged these branches according to their judgements of what was simple and what was complex. Sponges fell to the bottom branch, and bilaterally symmetrical animals resided higher up. But in 2008, a genetic analysis published in Nature put comb jellies, rather than sponges, near the root of the evolutionary tree.
This arrangement rattled evolutionary biologists because it upended the idea that animal complexity increased over time. It implied that nerves and other characteristics evolved independently in different lineages, and were subsequently lost in sponges. Since then, studies have supported or contradicted the rearrangement, but all have been plagued by problems.
Actually, there is no reason things could not have happened that way. It’s called devolution. It may be responsible for giant viruses. as well. The current group has attempted to rescue the sponges, using a Big Data crunch.
The results from the CAT model placed sponges on the earliest branch of the animal family tree. Some other models that the team used had put comb jellies at the base. “The fact that the results flip-flop with different models is a bad sign,” says Hillis, who was not involved with the work. More.
Yeah, we remember when the comb jellies had the sponges on the ropes, but oh boy, when the bell rings now, come outta yer corner fightin’! …
Seriously, the main thing is not to be swayed by a mere ideology that says that life forms had to become more complex over time. Yes, that is a general trend, but it is definitely not a law.
And if the original life forms turn out to be the most complex, well, we get to decide between ideology and evidence. Keeps people mentally active.
See also: Devolution: Getting back to the simple life
Comb jelly files: Complex features do not each emerge once
Comb jelly DNA sequence offers “unintuitive facts” about evolution…
Researchers: The sponge is the oldest animal phylum after all (2015)
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