Sponge v comb jellies: which was evolution’s first trailblazer?

New genetic research has reignited the controversy over which type of creature was the first to branch off the evolutionary tree from the common ancestor of all animals

While life on Earth has flourished for billions of years, much of it has been single-celled and microscopic. None of the first organisms had brains, or even neurons (nerve cells). None of them could think". The first animals to evolve were also brainless: harnessing hormones or other chemicals, rather than neurons, to coordinate their bodies. But some soon evolved central nervous systems - and the first thoughts" were pulsed.

For decades, biologists have assumed that this only happened once and was a one-way process. Once animals had evolved brains, why would they lose them? But in the past 15 years, evidence has accumulated that this may be wrong; that sponges and other brainless animals that exist today may be descended from brainy ancestors that lost their minds.