Did neurons evolve more than once on Earth?

[pErvinalia]

TRANSLUCENT comb jellies are some of the most primitive animals on Earth, yet they have remarkable nervous systems. Controversial data discussed at a meeting in London last month proposes that their neurons are unlike any others on Earth. This could be evidence that neurons evolved more than once in the history of animal life.

The suggestion that neurons evolved in parallel multiple times has divided biologists for over a century. Ultimately, Erich Jarvis of Duke University in North Carolina told a Royal Society conference in March, the question relates to how special we are. If neurons evolved several times on our planet, then it becomes more likely that they could evolve elsewhere in the universe.

Until recently, the consensus has leaned towards a very Darwinian story. In this scenario, sometime around 600 million years ago, the common ancestor to all animals gave rise to some organisms with simple neural networks. Central nervous systems arose later, allowing for greater coordination and more complex behaviours. These perhaps started out as tight balls of neurons, but eventually gave rise to the magnificently complex primate brain.

This single origin scenario offers a tidy explanation for why some animals, like sponges and flat, simple placozoans, still don't have neurons: they must have branched off before these evolved and are relics of ancestral animals (see diagram).

The story was somewhat turned on its head by the recent whole genome sequence of comb jellies. These small marine animals look like jellyfish but in fact seem to be only distantly related. They use a neural network just beneath their skin and a brain-like knot of neurons at one end to catch food, respond to light, sense gravity and escape predators.

When the first full genome of the comb jellyfish was published in December 2013, it suggested they had branched off from the animal family tree earlier than jellyfish, and before the brainless sponges. If comb jellies came first and sponges came later, says Leonid Moroz of the University of Florida at Gainsville, then either sponges lost their neurons or neurons were invented twice.

Moroz favours the second explanation. He and his team have taken a close look at the signalling molecules in comb jelly neurons and found that they are completely different to the ones used in all other neurons (Nature, doi.org/3cf). It's as if alien nerves were found right here on Earth, says Moroz. "If aliens landed on our planet, you would expect the chemical makeup of their brains to be different to any other nervous system."

But biologists are divided. Gáspár Jékely of the Max Planck Institute for Developmental Biology in Tübingen, Germany, and others still favour brainless sponges as the most primitive animals, maintaining that the genomic studies placing comb jellies as older are flawed.

http://www.newscientist.com/article/mg2 ... earth.html

[cronus]

There's still hope for some in my life then?

[rainbow]

There's still hope for some in my life then?

[cronus]

Superspreader logic.

[MiM]

I find it very fascinating how more and more pieces of evolution are found to have repeated themselves even here on earth. Feeds directly into the (overinflated) discussion of the big barrier.

[cronus]

I find it very fascinating how more and more pieces of evolution are found to have repeated themselves even here on earth. Feeds directly into the (overinflated) discussion of the big barrier.

Is it still there? Pity.