Brain-Signal Proteins Evolved Before Animals Did

Our human brains can seem like a crowning achievement of evolution, but the roots of that achievement are far deeper than that. The evolution of the nervous system can be traced back to the branch of the animal family tree that includes the bilaterians.

A recent discovery by a team of researchers in the United Kingdom has made it clear how long ago. All the major animal groups that preceded creatures with central nervous systems have the chemical precursors of two important neurotransmitters.

Single-celled relatives of animals, called choanoflagellates, contain these molecule. The evolution of the very first animals is shown by this finding.

There has been a long-standing question about when and how animal neuroscience evolved. It shows that some of the signaling molecule fundamental to the operation of our brains first evolved in organisms that only had one cell.

An animal's nervous system is made of neurons that connect to each other and a variety of smallpeptide neurotransmitters. The language with which the brain speaks is called the peptides.

The evolution of the neuronal molecule shows that the need for extensive communication between cell and cell began before this.

The murkiness of early animal evolution made it difficult for evolutionary biologists to deduce which animal cells used that language. Almost all of the early animal groups, including the ctenophores and the cnidaria, make a variety of molecules that are very similar toneuropeptides. Placozoans, which have no cells resembling neurons, make neuropeptides. Sponges seemed to be the only exception, which is why it was thought that animal neuropeptides originated in cnidarians or ctenophores.

The problem with that theory is that the neuropeptides in the early animal groups are not the same as the bilaterian ones. Many single celled animals make a wide variety of unrelated neuropeptides. The trail for brainpeptides disappeared into a thicket.

Luis Yaez-Guerra is a researcher in the lab of Gspr Jékely at the University of Exeter. Yaez-Guerra mapped the evolutionary tree of early-branching animals and their close relatives, the choanoflagellates.

He had already created a large list of animal neuropeptides, and as he began to look for them further down the animal tree, he realized that choanoflagellates made two mature neuropeptides.

The presence of neuropeptides in choanoflagellates was unexpected. It is more difficult to comprehend in a unicellular organisms. The evolution of the neuronal molecule shows that the need for extensive communication between cell and cell began before this. It was shocking because of that.