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 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” 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.
