Re: Ch.7: Epigenetic rules (Help!)
The fundamentals of evolutionary theory were laid down by Darwin before anyone had even a clue as to what a physical gene was. The validity of the theory was established by the results: the relationships between creatures that were best explained by selection of random, small modifications.
Now we know what physical genes are, and in certain very specific cases we can link a specific physical gene to a specific result in the genotype. Knock out gene "a" and get a mouse that can't produce protein "b"; therefore, the purpose of "a" is to produce "b".
However, these interactions are rare. Most genetic effects are the result of many different genes, acting on each other in complex feedback loops. However, we can still make valid inferences about what must be going on "under the hood" long before we are able to link the details. For example, the concordance of monozygotic twins for autism is between 80 and 100%, depending on who's interpreting the results. Given these facts, we know for sure that autism has a major genetic component. We also know that a complex suite of behaviours is guided by many, many genes at many different levels. Therefore, we it is a valid conclusion that there is a real epigenetic rule at work.