Epigenetics: Wondrous, Not Revolutionary

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Epigenetics is the study of changes to DNA molecules that do not involve mutations or the changing of nucleotides. Currently, epigenetics seemed to have surpassed the related field of developmental biology as staking claim to being the new revolution in evolution. (IDists, you still have a way to go to become a scientific fad. You gotta drop the bullhorn and start doing some science.)

I’m with Jerry Coyne; call me unfashionable, but my response to these fads is “meh.” In fact, Dr. Coyne has done a great job in discussing why these findings make evolutionary biology more wondrous, but don’t disrupt evolutionary biology or the central place of Darwin’s theory of natural selection has in it.

Dr. Coyne places the blame of these fads on science journalists, but I would go further and place additional blame on scientists themselves. It is my opinion, that much of this “Darwin to the doghouse” rhetoric begins with the scientists, specifically ones who have no background in evolutionary biology—say biophysicists or molecular biologists with a mostly biochemistry background. These are the ones who are likely to have just enough knowledge to think they understand evolution, and thus are mistakenly confident to say that they are overturning it. (And I shouldn’t forget the physicists and engineers, who always know better than us “soft” scientists.)

These people exist because many college programs in the biological sciences don’t even require a course in evolutionary biology. (Seriously! Are they afraid that the pre-meds will revolt?) Until that changes, we will still be training too many biologists and physicians whose knowledge about evolution is gathered more from television than the classroom.

6 Comments

I have a somewhat different opinion. I would blame the pressure on scientists to make their work sound revolutionary – gets you into Nature, and satisfies whoever makes university press releases. Ignorance of evolution isn’t required, just a desire to please.

The pressure on scientists to announce that their work inavlidates all previous science is part of the problem – it then interacts with the desire many people have to do away with the Modern Synthesis. The result is a Perfect Storm.

What Jerry Coyne is seeing clearly is that epigenetic modifications can’t be the basis of long-term evolution, since they revert after about 3-4 generations. Only if some genetic change accompanies them can they become permanent.

To keep an epigenetic modification at reasonable frequency in the population requires very strong selection. We can check this with a simple model of (epigenetic) “mutation” back and forth between presence and absence of the modification. If the forward “mutation” rate is 0.0001 and the “back mutation” rate is 0.25, then if the fitnesses of “heterozygotes” are intermediate between the two “homozygotes”, you need 50% loss of the unmodified “allele” per copy just to keep the frequency of the epigenetic modification above 2/3.

There have been some papers on population genetics of epigenetic modifications. The ones I found were:

# Slatkin, M. 2009. Epigenetic inheritance and the missing heritability problem. Genetics 182 (3): 845-850.

# Tal, O., E. Kisdi and E. Jablonka. 2010. Epigenetic contribution to covariances between relatives. Genetics 184 (4): 1037-1050.

# Carja, O. and M. W. Feldman. 2011. An equilibrium for phenotypic variance in fluctuating environments owing to epigenetics. Journal of the Royal Society Interface, Published online before print August 17, 2011, doi: 10.1098/​rsif.2011.0390.

Mostly they concern the very real biasing of heritability estimates by unacknowledged epigenetic variation. There have been few calculations of long-term change, mostly because there will be so little of that.

I’m just starting to wade into epigenetics on a sabbatical. I agree that I don’t see it having much impact on evolutionary (population) questions. It seems more likely to be beneficial in answering questions about rapidly changing phenotypes of individuals; epigenetic modifications of gene expression may underlie the extreme addictive potential of cocaine, for example. Some individuals may be more susceptible to those modifications, and therefore more likely to become addicted. I downloaded a few papers looking into epigenetic contributions to sexual orientation as well, but haven’t had a chance to read those.

Joe Felsenstein said:

The pressure on scientists to announce that their work inavlidates all previous science is part of the problem – it then interacts with the desire many people have to do away with the Modern Synthesis. The result is a Perfect Storm.

What Jerry Coyne is seeing clearly is that epigenetic modifications can’t be the basis of long-term evolution, since they revert after about 3-4 generations. Only if some genetic change accompanies them can they become permanent.

Epigenetics doesn’t help ID one bit, for precisely the above reasons. The only reason IDers push it like they also push HGT is that the general public isn’t equipped to see through this intellectually bankrupt ploy. They truly disgust me.

There are a number of basic concepts in Darwin’s thinking. Two of the more significant ones are:

1: There is no fixity of species. All existing species arose from preexisting species, along paths that form a “tree” rooted in common ancestry.

2: They did so spontaneously and with no direction other than towards improved fitness to their local environments.

These are the basic sticking points for anti-evolution advocates: species were not created in part or whole, and nobody is in charge of the process. All discoveries in 150 years of proper evo science have only reinforced these two premises, and of course any discussion of incidental details like epigenetics will do nothing to affect them. I suppose talk of “revolutionary findings” is amusing, but the downside is that it seems to give support to the ID crowd when it flatly doesn’t.

I read an article on this a while back in a “science for the public” magazine. The gist of it was that while Lamarck was wrong, he might not have been quite as wrong as was previously believed.

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This page contains a single entry by Reed A. Cartwright published on August 25, 2011 9:00 AM.

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