Genetics aren’t the only triggers for the traits a species develops, according to findings from a University of Alberta professor. The research challenges the classical Darwinian theory of evolution as being the sole explanation for how new life forms arise.
“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.”
What on earth? I can’t get to the letter from home, so perhaps that will clear up my confusion when I read it at work tomorrow, but I’m not seeing anything there that conflicts with the standard model of evolution or indicates that “genes follow form”. That last smacks of Lamarckism to me. The lobster inherited the genetic basis on which one or the other claw hypertrophies, and it’s not hard to see how that would convey a selective advantage. The right- and left-sided forms inherited the basis of those forms; that the asymmetry distributes evenly among offspring of same-sided parents implies that the environmental triggers did not alter the genotype. Skin cancer and mesothelioma, when they are induced by environmental insult, arise from environmentally induced mutation: phenotype follows genotype. I’m looking forward to reading that letter.
Update: the letter from Palmer and response from Lewontin were a red herring, I just didn’t see the review article when viewing the site without paid access. The EurekAlert article refers to this review by Palmer that appears to be, at least in part, bunk. Here’s the abstract:
Because of its simplicity, the binary-switch nature of left-right asymmetry permits meaningful comparisons among many different organisms. Phylogenetic analyses of asymmetry variation, inheritance, and molecular mechanisms reveal unexpected insights into how development evolves. First, directional asymmetry, an evolutionary novelty, arose from nonheritable origins almost as often as from mutations, implying that genetic assimilation (“phenotype precedes genotype”) is a common mode of evolution. Second, the molecular pathway directing hearts leftward