The Imprinted Brain

How genes set the balance between autism and psychosis

Epigenetics: It's nonsense without evolution!

DNA doesn’t copy you, whatever epigenetics seems to say

Darwin believed it even though Galton experimentally disproved it—and had the right idea in his so-called “Stirp” theory of inheritance. Freud stubbornly stuck to it despite repeated protests from Ernest Jones. And Lysenko destroyed Soviet biology and agriculture with it. Indeed, the Stalinists exiled, tortured, murdered, and starved millions in its name, which it got from Jean-Baptiste Lamarck (1774-1829), the great French naturalist. So today we call it Lamarckism, and it means the inheritance of acquired characteristics.

In Darwin’s view "the constant inculcation in a belief in God on the minds of children" produced "so strong and perhaps an inherited effect on their brains not yet fully developed, that it would be as difficult for them to throw off their belief in God as for a monkey to throw off its instinctive fear and hatred of a snake."  This is not just the conventional platitude about nurture and nature working together, but nurture turning into nature and becoming instinctive, thanks to a Lamarckian mechanism of inheritance which Darwin called pangenesis. (See my Evolutionary Psychology for more details and examples.)

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Lamarckism is what you might call photocopier genetics: it assumes that genes copy organisms the way photocopiers copy documents. But of course this is impossible for three good reasons. First, nothing scans the organism to acquire the image to be copied (although Darwin thought there were such things, and called them gemmules). Second, there is no original to copy as there is with a document—people change continuously, and no one moment can be taken as an epitome or prototype. Third, even if you did have an original, DNA would have to know what to copy and what to ignore—such as injuries or ageing—and that would be like expecting a photocopier only to copy correctly spelt words. Impossible, however you look at it!

Theodore Dobzhansky famously remarked that nothing in biology makes sense except in the light of evolution, and nowhere is this more true than in relation to genetics. This is because, according to our modern, “selfish gene” view of evolution, organisms evolved to copy their DNA, rather than DNA evolving to copy the organism. Immediately all kinds of things inexplicable to photocopier heredity make sense: “junk genes,” “jumping genes,” “nonsense” DNA, etc. etc.

But Lamarckism still appeals. As an article entitled “Sins of the fathers” in this week’s New Scientist asks, “What if your bad habits mean that your children and even their children end up with a psychiatric disorder?” (6 November pp. 8-9). Think of all the moralizing, naming-shaming-and-blaming you could do if this were true! What a gift to personal injury lawyers and any offended group with a compensation axe to grind! What a vindication for healthy-life-style campaigners and the Victorian belief in self-improvement-in-the-interests-of-improving-the-race! Were Freud, Lysenko, and Lamarck right after all?

The New Scientist article was all about epigenetics: the mechanisms of gene expression, rather than simply inheritance. Today we know that there are three major mechanisms: X-chromosome gene inactivation, genomic imprinting, and copy number variation. In the case of both X-inactivation and imprinting, epigenetic markers are usually re-set each generation. But when this mechanism fails or goes awry, many discussions of epigenetics interpret the results as evidence of a quasi-Lamarckian mechanism of inheritance because of the way such epigenetic changes appear to be heritable. Indeed, I invoked lingering X-inactivation myself as a possible explanation of the inheritance of Asperger’s syndrome in a previous post—but needless to say, without any concessions to Lamarckism!

But some interpreters are not so circumspect and claim that epigenetics vindicates Lamarckism. For example, some argue that "there are mechanisms that enable the genome to sense an environmental change, respond to it, and transmit the response to descendants.” This is just what Lamarck supposed and Lysenko believed he had proved in his famous vernalization procedure by which crops were nurtured to tolerate cold weather.  

Of course, this is complete nonsense, as I pointed out 15 years ago in my review of the book from which I quote above. In the meantime though, epigenetics really seems to be catching on in the popular mind, as this week’s New Scientist coverage suggests. And it’s easy to see why: it is presented as perpetuating the photocopier view of genetics which so appeals to people’s everyday way of thinking. Who wants to see themselves as the temporary custodian of their genome, the copier of their DNA, or the bio-degradable packaging of their genes? 

The truth is that if nothing in genetics makes sense without evolution, then epigenetics without evolution is complete nonsense. Only an evolutionary perspective can explain why epigenetic mechanisms like imprinting should disable otherwise vital backup copies of key genes like IGF2 mentioned in the New Scientist article. This is the gene I invoked in my original review, and this is the paradigmatic gene where the imprinted brain theory in particular and the conflict model of epigenetics in general is concerned. What New Scientist does not tell you is that IGF2 is only normally expressed from the father’s copy. IGF2 codes for a growth hormone whose benefits accrue to both parents, but whose costs are only paid by the mother. And of course, this is why the mother silences this gene so that only the paternal copy is expressed. Photocopier heredity can’t explain this, but evolution can, as I explain at length in my book.

Indeed, as I also explain at even greater length, the evolutionary interpretation of epigenetics enables you to explain its role in mental health and illness without any mention of the sins or bad habits of the fathers, or of the mothers for that matter—"refrigerator" ones included!

 

 

 

 

Christopher Robert Badcock, Ph.D., is author of The Imprinted Brain: how genes set the balance between autism and psychosis. 

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