I don’t know who the New York Review of Books is getting to vet its biology articles, but this one below (free access) is really confusing. One reason may be that the authors have no particular expertise in evolution. Israel Rosenfeld is an MD with training in neuroscience, while Edward Ziff is a professor at NYU who works on neural transmission. I’ve never heard of either of them, which doesn’t rule them out as being able to say anything useful about evolution, but I usually am familiar with people who write about evolution for the NYRB, and they always had a name in evolutionary biology (viz., my student Allen Orr). Anyway, here’s the article (click on screenshot to see it).
The problem with this article is that it’s deeply confused, conflating gene regulation within the lifetime of an individual (which can be achieved by “epigenetically” attaching or detaching methyl groups to genes to turn them on or off) with environmentally induced modification of the DNA that is inherited over several generations, causing a form of “non-Darwinian” evolution.
The former is not problematic; we’ve long known that genes can be regulated by environmental factors; that’s what Jacob and Monod got their Nobel Prizes for. We’ve learned more recently that this regulation can also be programmed to cause methylation: genes are adaptively activated and deactivated by the attachment of methyl groups (or small RNA molecules) to segments of genes. But even that adaptive regulation is coded for by DNA. That is, there are genes which are programmed to turn other genes on or off by adding small molecules to them. That’s the way cells differentiated so that even though all cells have the DNA, some become liver cells, others brain cells or blood cells, and so on. That is permanent changes in gene regulation occurring largely by methylation, and over generations of cells, but not over generations of individuals. Such differentiation within an individual still evolved in a Darwinian way, it’s just that natural selection favored particular ways to adaptively activate or inactivate genes.
However, a vocal group of biologists maintain that evolution can also occur when the environment rather than DNA (extrinsic factors like cold or starvation) can methylate genes too, and that methylation can be inherited. The problem with this, as I’ve emphasized repeatedly, is twofold. First those environmental changes are nearly always nonadaptive or maladaptive—they’re more like random screwups—and so can’t be the basis of adaptive evolution.
Second, environmentally induced changes in DNA are nearly always wiped out during gamete formation, and so those changes cannot be the basis of long-term evolution or adaptation. There are a few exceptions, but I don’t know of any such modifications that can last longer than three generations. The fact that this form of “Lamarckian” inheritance isn’t pervasive is also shown by the numerous adaptations that have been dissected genetically: all of them are based on changes in the DNA sequence rather than attachment of methyl groups induced by the environment.
Rosenfield and Ziff conflate the programmed regulation of genes by other genes that induce methylation with the “Lamarckian” changes in DNA sequence. That’s clear when they say stuff like this:
Until the mid-1970s, no one suspected that the way in which the DNA was “read” could be altered by environmental factors, or that the nervous systems of people who grew up in stress-free environments would develop differently from those of people who did not. One’s development, it was thought, was guided only by one’s genetic makeup. As a result of epigenesis, a child deprived of nourishment may continue to crave and consume large amounts of food as an adult, even when he or she is being properly nourished, leading to obesity and diabetes. A child who loses a parent or is neglected or abused may have a genetic basis for experiencing anxiety and depression and possibly schizophrenia. Formerly, it had been widely believed that Darwinian evolutionary mechanisms—variation and natural selection—were the only means for introducing such long-lasting changes in brain function, a process that took place over generations. We now know that epigenetic mechanisms can do so as well, within the lifetime of a single person.
This is deeply confusing, for it conflates gene regulation within an individual with evolutionary changes that evolve over many generations. In fact, the epigenetic regulation mentioned by Rosenfield and Ziff did evolve over generations by natural selection. They are saying that two things are distinct and contradictory when in fact they are the same thing. It’s no surprise that this article (which is largely written in technical jargon) would confuse the layperson.
Likewise, single-generation screwups induced by the environment in adults that affect their children have nothing to do with natural selection or evolution (note that “evolution” is in the article’s title). Even if those changes induce modification of their children’s DNA, this one-generation effect does not persist after that, and has nothing to do with evolution:
The most revealing instances for studies of intergenerational transmission have been natural disasters, famines, and atrocities of war, during which large groups have undergone trauma at the same time. These studies have shown that when women are exposed to stress in the early stages of pregnancy, they give birth to children whose stress-response systems malfunction. Among the most widely studied of such traumatic events is the Dutch Hunger Winter. In 1944 the Germans prevented any food from entering the parts of Holland that were still occupied. The Dutch resorted to eating tulip bulbs to overcome their stomach pains. Women who were pregnant during this period, Carey notes, gave birth to a higher proportion of obese and schizophrenic children than one would normally expect. These children also exhibited epigenetic changes not observed in similar children, such as siblings, who had not experienced famine at the prenatal stage.
During the Great Chinese Famine (1958–1961), millions of people died, and children born to young women who experienced the famine were more likely to become schizophrenic, to have impaired cognitive function, and to suffer from diabetes and hypertension as adults. Similar studies of the 1932–1933 Ukrainian famine, in which many millions died, revealed an elevated risk of type II diabetes in people who were in the prenatal stage of development at the time. Although prenatal and early-childhood stress both induce epigenetic effects and adult illnesses, it is not known if the mechanism is the same in both cases.
Whether epigenetic effects of stress can be transmitted over generations needs more research, both in humans and in laboratory animals. But recent comprehensive studies by several groups using advanced genetic techniques have indicated that epigenetic modifications are not restricted to the glucocorticoid receptor gene. They are much more extensive than had been realized, and their consequences for our development, health, and behavior may also be great.
First, “intergenerational transmission” of this sort has been known for a while: smoking, alcohol, thalidomide, and now famine, can screw up the health of the next generation. But those changes disappear after that. They are not, as the authors admit in the last paragraph, something that’s “transmitted over generations.” But they must be transmitted over generations if they’re to cause evolution.
The authors are a bit weaselly here in saying “whether epigenetic effects can be transmitted over generations needs more research”, when we already know from many studies that they’re almost always never transmitted over generations. Why didn’t they admit that? I presume because they have a bill to sell.
To complete the confusion (I doubt that many NYRB readers have even gotten to this point), Rosenfield and Ziff imply that adaptive epigenetic modification of genes is something distinct from Darwinian natural selection. But, as I’ve said, it is Darwinian natural selection that molds the adaptive regulation of genes: genes tell other genes when and how to be regulated. So read the following paragraph and see if you can make out what the authors are trying to say:
It is as though nature employs epigenesis to make long-lasting adjustments to an individual’s genetic program to suit his or her personal circumstances, much as in Lamarck’s notion of “striving for perfection.” In this view, the ill health arising from famine or other forms of chronic, extreme stress would constitute an epigenetic miscalculation on the part of the nervous system. Because the brain prepares us for adult adversity that matches the level of stress we suffer in early life, psychological disease and ill health persist even when we move to an environment with a lower stress level.
It is not “nature” that employs epigenesis, but genes that have resulted from natural selection. What do they mean, exactly, by “nature.” I’ve read that paragraph several times, and I still can’t figure out what the authors are trying to say, especially in the last sentence. It seems to imply that ill health of children induced by parental environments that persists in low-stress situations is a byproduct of natural selection that adapted us for adversity as adults, and that it has to be that way. But it doesn’t. The paragraph is gobbledy-gook, and an example of bad and confused writing.
This wouldn’t have happened had this piece been edited by the venerable Bob Silvers, the longtime NYRB editor, famous for his punctilious editing, who died last year. There’s a new editor now, and he’s pretty tetchy when criticized, so I’ll expect I’ll get some flak for criticizing this piece. But read it for yourself, and see if, as a non-biologist, you can make sense of it. I am a biologist, and am deeply confused by it.
There’s no excuse for popular science writing that is this bad and confusing. I’d suggest to the new editor, Ian Buruma, that he choose his science writers more carefully. Epigenetics simply has not caused a “revolution in evolution.”
Here’s an evolutionary geneticist, and a really good one, who also read the piece:
— Graham Coop (@Graham_Coop) May 24, 2018