Friday, July 2, 2010
Why Fish Came Ashore
By SINDYA N. BHANOO
Published: June 28, 2010
About 365 million years ago, the fins of some fish evolved into limbs, creating a class of animals known as tetrapods that left the water to dwell on land, giving rise to amphibians, reptiles, birds and mammals.
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A mouse embryo's budding limb lacks the genes found in some fish.
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But just how fins turned to limbs has been a subject of great interest in evolutionary biology.
A new study in the journal Nature reports that a genetic defect in certain fish may have stunted fin growth and led to the development of limbs and the emergence of land dwelling creatures.
Using zebrafish, researchers inhibited the activity of a set of genes in developing embryos. Fin growth was greatly reduced, leaving room for limbs to develop.
“If this kind of gene expression happened in an ancestral fish that may have led to limb development,” said Marie-Andree Akimenko, a biologist at the University of Ottawa in Canada and one of the study’s authors.
The set of genes seem to code for the proteins that lead to the development of actinotrichia, fibers that provide structural support for the formation of fin rays, the rigid bones that make up a fin.
The absence of these genes, found in other fish but not in any land-dwelling animals, may have allowed for limb development.
Next, Dr. Akimenko hopes to introduce this set of genes into mice embryos to see what happens.
Fossils of some early land dwellers show eight digits at the ends of each limb, rather than the five that most tetrapods have today. Further research may shed more light on how and why this occurred, she said.
This article has been revised to reflect the following correction:
Correction: June 30, 2010
A report in the Observatory column on Tuesday about the evolution of some fish into a class of four-limbed animals (known as tetrapods) referred incorrectly to appendages of early land-dwelling creatures and modern animals. The early creatures typically had eight digits per limb, compared with five on modern tetrapods — not eight limbs versus five limbs.
...the magic of self-forming life...!
...synonymous to "wishful thinking"...!
...like i wish i had not even been born...!
...or we wish he had never been born...!
...this article of big mutations, thought
technically possible, really only proves further
how ignorant Science Evolution is today "more than
ever" and that the more they try to explain
Evolution, it comes down by it's own weight...!