herebedragons writes:
It has been explained that epigenetics is not the same thing as mutation. Now you complain that no one is presenting the evidence for mutations being random.
I just read up a little bit (a very little bit) on epigenetic inheritance to understand how it creates heritable changes if the underlying DNA sequence remains unchanged, and one of the examples was
DNA methylation. As explained by Wikipedia:
Wikipedia writes:
It involves the addition of a methyl group to the 5 position of the cytosine pyrimidine ring or the number 6 nitrogen of the adenine purine ring (cytosine and adenine are two of the four bases of DNA). This modification can be inherited through cell division.
If we define mutations as changes to the DNA sequence of nucleotides then this kind of change is not a mutation, but it
*is* a change in the DNA, it
*is* heritable, and it
*can* be caused by the environment. The
Wikipedia article on Epigenetics argues at one point that if the genetic code represents the DNA sequence then the "epigenetic code" represents the total state of the cell.
Wikipedia mentions of the environment affecting epigenetic factors mostly mean the local cell environment. For single-celled non-communal organisms one could argue that the environment can guide evolution directly, but anything above this level is much more complicated. Most epigenetic discussion that I read was about internal chemical changes during fetal and juvenile development that turn processes on and off. For any external environmental changes to influence internal cellular processes in, say, a mammal would likely require a long chain of internal effects.
Zi Ko should pick an example of epigenetic inheritance so we have something concrete to talk about.
--Percy