Slipper Lobster. Credit: Norfanz.
Slipper Lobster. Credit: Norfanz. |
In a paper published October 29 in the journal Science, Dr. Richard Palmer, a U of A professor of biological sciences, says studies of hundreds of species have shown that a creature's environment can be just as key in creating differences, also known as variations.
"Variations that do not initially have a genetic basis can still be important for evolution. They are 35 to 50 per cent as common as genetic variation, at least when it comes to the evolution of asymmetric forms" Dr. Palmer said.
He was able to synthesize published evidence showing that the current 'genotype-precedes-phenotype' theory of evolution only explains about half of the examples he studied.
He came to his conclusions after reviewing more than 200 research papers from around the world, including a study on asymmetry (the difference between the left and right sides of the body) that was conducted using lobsters.
Baby lobsters are born with two same-sized claws, but somehow, only one of the claws transforms into a larger crusher claw as the lobster grows.
"The genetic program that makes a crusher claw is triggered by one claw being used more than the other. But if one side isn't stimulated enough, the program that makes a crusher claw never gets started. It's a clear example of how environment in some sense causes difference in form," Dr. Palmer said.
Further, studies on many other plant and animal species with both right-sided and left-sided forms showed that if two of the same 'handedness' were mated, half their offspring would be left-sided and half would be right-sided.
"Genetics made no difference in the direction of asymmetry. It's a trait strictly determined by environment. From an evolutionary perspective, this means form arises first and the genes follow."
These observations have some parallels with modern medical research, Palmer said. "You can't say all diseases are gene-based. Consider cancer caused by asbestos exposure, or skin cancer. If you only study genetics, you would not learn much about environmentally-induced diseases."
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