|The comb jelly could only have achieved its apparent seniority over the simpler
sponge via one of two new evolutionary scenarios: 1) the comb jelly evolved its
complexity independently of other animals, after it branched off onto its own
evolutionary path; or 2) the sponge evolved its simple form from more complex
creatures--a possibility that underscores the fact that evolution is not necessarily
just a march towards increased complexity, says Dunn. This scenario would provide a
particularly dramatic example of that principle.
Credit: Zina Deretsky, NSF