Interesting news confirms earlier speculations
Public release date: 20-Apr-2007
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Contact: Anna-Lynn Wegener
European Molecular Biology Laboratory
Researchers discover that the centralised nervous system of
vertebrates is much older than expected
The rise of the central nervous system (CNS) in animal evolution has
puzzled scientists for centuries. Vertebrates, insects and worms
evolved from the same ancestor, but their CNSs are different and were
thought to have evolved only after their lineages had split during
evolution. Researchers from the European Molecular Biology Laboratory
(EMBL) in Heidelberg now reveal that the vertebrate nervous system is
probably much older than expected. The study, which is published in
the current issue of Cell, suggests that the last common ancestor of
vertebrates, insects and worms already had a centralised nervous
system resembling that of vertebrates today.
Many animals have evolved complex nervous systems throughout the
course of evolution, but their architectures can differ substantially
between species. ...all these species descend from a common ancestor
called Urbilateria. If this ancestor already possessed a nervous
system, what it might have looked like and how it gave rise to the
diversity of nervous systems seen in animals today is what Detlev
Arendt and his group study at EMBL. To do so, they investigate the
nervous system of a marine annelid worm called Platynereis dumerilii.
"Platynereis can be considered a living fossil," says Arendt, "it
still lives in the same environment as the last common ancestors used
to and has preserved many ancestral features, including a prototype
invertebrate CNS. Comparing the molecular fingerpint of Platynereis
nerve cells with what is known about vertebrates revealed surprising
"Our findings were overwhelming," says Alexandru Denes, who carried
out the research in Arendt's lab. "The molecular anatomy of the
developing CNS turned out to be virtually the same in vertebrates and
Platynereis. Corresponding regions give rise to neuron types with
similar molecular fingerprints and these neurons also go on to form
the same neural structures in annelid worm and vertebrate."...
The findings provide strong evidence for a theory that was first put
forward by zoologist Anton Dohrn in 1875. It states that vertebrate
and annelid CNS are of common descent and vertebrates have turned
themselves upside down throughout the course of evolution.
"This explains perfectly why we find the same centralised CNS on the
backside of vertebrates and the bellyside of Platynereis," Arendt
says. "How the inversion occurred and how other invertebrates have
modified the ancestral CNS throughout evolution are the next exciting
questions for evolutionary biologists."
To continue, with slight clarification, if interested:
See Neil Shubins slideshow, especially page 6 slide 5, to compare Hox gene positions in human and fruit fly.
My earlier explanation of primitive pentadactylity (5 digits) didn't well cover the duplication of reptile/mammal rear limbs from the forelimb carriage, this duplication is actually the same as the duplication of (beetle) 4 wings / 4 jaw mouthparts from the primitive frontal digits.