Science News Archive

Humans have worm-based brains

For some of us, feeling like we have the brain of a worm is a common experience.  But new research has shown that our brains may actually have evolved from worms, making the origins of the nervous system much older than previously thought.
Vertebrates like us, insects and worms evolved from the same ancestor, but their central nervous systems are different and were thought to have developed only after the split. But new research from the European Molecular Biology Laboratory (EMBL) in Heidelberg now suggests that the last common ancestor of vertebrates, insects and worms already had a centralised nervous system similar to that found in vertebrates today.
The last common ancestor we shared with worms an insects was a simple creature called Urbilateria.  Since then, vertebrates have developed a nervous system with a brain and a spinal cord running down the back, while worms and insects have a rope-laddder-like chain of nerve cell clusters running down the belly.  And other insects have even stranger nervous systems, made of nerve clusters all over the body.   So how did all these systems spring from one ancestor, Urbilteria? And what did Urbilateria’s nervous system look like?
To answer this, the researchers, led by Detley Arendt, studied a simple sea worm, called Platynereis dumerilii.  Platynereis can be thought of as a kind of “living fossil”, which still lives in the same environment as the last common ancestors like Urbilateria. The worm also has a prototype invertebrate nervous system, thought to similar to that in our common ancestor.
Arendt and his group investigated how the developing nervous system in Platynereis embryos gets subdivided into the regions that later on give rise to the different nervous structures. The researchers studied the genes involved in the process, and compared them with the genes that control the development of the vertebrate nervous system. They found some surprising similarities, showing that the molecular landscape in the developing nervous system is virtually the same in vertebrates as in the Platynereis worms.
The researchers argue that such a complex arrangement could not have been invented twice throughout evolution, so it must be the same system at work, hat has been inherited from our primitive shared ancestor.  The next challenge is to figure out why worms have their nervous system in their bellies, while vertebrates have theirs in the back.

21st Apr 2007