Epigenetics Comes of Age

Evolutionary Changes Involve no Changes in Genes

The crux of the process of evolution is how the novel evolutionary change occurs. The conventional explanation given is by specific changes in genes, gene mutations. Although this is taken for granted and self-evident no one has ever shown either in theory (in concrete causal terms) or illustrated with concrete examples how a change in a particular gene brought about an evolutionary change.

Creationism has been the real beneficiary of this doctrinaire stance.

What is an evolutionary change? Most biologists would agree that, essentially, it is a new/changed phenotypic character that appears in the offspring of parent(s) that did not possess it and is transmitted over generations, independently of the environment in which it first appeared.

Unfortunately, often the emergence of the evolutionary change, which is the real problem of evolution, is confused with the selection and spread of existing alleles studied in populations genetics. The focus on the spread of alleles in natural populations, the easy side of the problem, which is already understood in principle, tends to divert attention from the mechanisms of emergence of evolutionary change, the real core of the evolutionary process.

It is commonly said that the main difficulty in our attempts to demonstrate the occurrence and the mechanism of evolutionary change is the fact that evolutionary (=inherited) changes in phenotypic characters are relatively rare phenomena requiring many generations and, by human life-time standards, long times. Hence, evolutionary changes, as a rule, cannot be experimentally reproduced and observed in nature or in experiments.

However, if the definition of the evolutionary change essentially implies a heritable change in a phenotypic character then evolutionary changes are neither rare nor random phenomena. They can be observed and experimentally reproduced not randomly but deliberately planned and induced. Most importantly, empirical evidence shows that induction of these evolutionary changes involves no changes in genes, contrary to the conventional assumptions of gene mutations as causes of evolutionary changes in metazoans.

This is supported by and illustrated with described and well studied cases of transgenerational developmental plasticity. The fact that these sudden heritable changes affect whole populations simultaneously clearly excludes changes in genes or genetic information in general, clearly indicates that this type of inheritance is epigenetic in origin and nature and epigenetic is also the information that brings about new heritable characters in the offspring. Sudden appearance of new characters affecting not rare individuals but whole populations of a generation is not reconcilable with the basic tenet of the gradualism and randomness of genetically determined evolutionary changes.

In chapter 12 of Epigenetic Principles of Evolution a considerable number of cases of sudden new/changed phenotypic characters that appear first in the offspring of parents that are exposed to specific environmental stimuli or environmental stress and are transmitted to further generations even in the absence of environmental conditions that stimulated induction of the new/changed characters. Such cases of transgenerational developmental plasticity, essentially represent cases of evolutionary changes in phenotypic characters and these evolutionary changes involve no changes in genes or genetic information.

It may be argued that examples of transgenerational plasticity presented in the book represent “exceptions to the rule”.

However, there are numerous cases of evolution of characters without changes in genes. Birds have lost their teeth although it is experimentally demonstrated that all the odontogenic genes are functional in this vertebrate class; loss/reduction of limbs in aquatic mammals has not been proven to be causally related to any changes in genes, etc.

Moreover, there are no demonstrated cases of changes in a particular gene that have led to a particular evolutionary change in animal morphology. Empirical evidence especially in last two decades is showing that the metaphor of the “genetic tool kit” ironically proves the opposite of what it was intended to. Epigenetic mechanisms seem to represent the “wise user” of the “genetic tool kit” . Long before, with rare clairvoyance,  Medawars noticed this and aphoristically expressed the idea that “Genetics proposes, epigenetics disposes”.

This entry was posted on Sunday, June 27th, 2010 at 5:17 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.