People who read the series and then write to me, write more often than not about one of two things. The first is the question of whether the conspiracy is plausible — which is the question I take up in the He Jiankui post that ran yesterday. The second is the question of whether genetic memory is a real thing.
I want to answer the second question carefully, because the honest answer is more interesting than either of the unhelpful short answers (the dismissive "no, it's fiction, don't be silly," and the over-credulous "yes, look at these studies in mice"). The honest answer is that there is a small but real body of evidence for a phenomenon that resembles what the novels portray, that the evidence supports much less than the novels portray, and that the gap between what is proven and what the novels treat as true is the entire imaginative engine of the series.
What Epigenetics Actually Is
Your DNA does not by itself determine which proteins your cells produce. The same genome runs every cell in your body — your neurons and your liver cells and your skin cells all have identical DNA — and yet those cells do very different things. The difference comes from epigenetics: chemical modifications layered on top of the DNA that determine which genes are expressed in which cells under which conditions.
The two most studied epigenetic mechanisms are DNA methylation (chemical tags that silence specific gene regions) and histone modification (changes to the proteins that DNA wraps around, affecting whether the DNA in that region is accessible to be read). Both of these mechanisms can be altered by environmental factors. Diet affects methylation patterns. Stress affects methylation patterns. Toxin exposure affects methylation patterns. Some of these alterations are temporary; some persist for the life of the cell; some persist across multiple cell divisions.
This is uncontroversial. It has been in undergraduate biology textbooks for two decades. The question that animates the more contested research is whether these epigenetic patterns can be inherited by offspring.
What Transgenerational Epigenetic Inheritance Looks Like
The strongest evidence for transgenerational epigenetic inheritance in humans comes from natural experiments — historical episodes where large populations experienced a sudden severe environmental stress, after which researchers can look at the descendants of the people who were exposed and ask whether the descendants show measurable physiological or behavioral differences.
The most famous of these is the Dutch Hunger Winter of 1944–1945. During the last winter of the German occupation, the Netherlands experienced a coordinated food blockade. Daily caloric intake in the affected regions fell to around 400–800 calories per person. Approximately 22,000 people died of starvation. The famine ended abruptly in May 1945 with the liberation. The Dutch government, which is excellent at keeping records, has comprehensive medical data on the people who were in utero during the famine and on the multiple generations descended from them.
What the Dutch Hunger Winter studies show is striking. People who were in utero during the famine, particularly during the first trimester, show measurable differences in their adult health compared to siblings born before or after the famine. They have higher rates of obesity, higher rates of cardiovascular disease, higher rates of type 2 diabetes, higher rates of schizophrenia. They have measurably different methylation patterns at specific genes related to metabolism — the IGF2 gene in particular shows persistent hypomethylation in famine-exposed individuals six decades after the exposure.
More striking still: the children of the famine-exposed women — meaning the grandchildren of the women who were pregnant during the famine — show some of the same physiological signatures. The famine's effect, in other words, did not stop at the directly exposed generation. It propagated forward.
Similar findings exist for the Överkalix studies in Sweden (which tracked the children and grandchildren of people who experienced severe famines in the 1860s), for the children of Holocaust survivors (who show altered stress-response profiles at the methylation level), and for the children of fathers exposed to certain wartime traumas.
The mechanism by which environmental stress in one generation produces physiological consequences in the second and third generations is not fully understood. But the empirical observation — that it happens — is now reasonably well established.
What This Evidence Does Not Support
This is where I have to be honest about the gap between the science and the fiction.
The transgenerational epigenetic inheritance demonstrated by the Dutch Hunger Winter studies and their analogs is a general physiological effect. It changes how the descendant's body handles food, stress, immune response, and certain disease risks. It does not, in any study I am aware of, transmit specific information about the originating event. The grandchild of a Hunger Winter survivor cannot tell you that her grandmother starved; she can only show, at the molecular level, that her own body is operating in a metabolic mode optimized for an environment that no longer exists.
There is a vast distance between "your body inherited a generalized stress signature from your grandmother's famine" and "you remember the famine."
The mouse studies sometimes cited in popular accounts of genetic memory have to be read with the same care. The famous Dias and Ressler study, published in Nature Neuroscience in 2013, showed that mice conditioned to fear the smell of cherry blossom (specifically, acetophenone) produced offspring and grand-offspring who showed elevated startle responses to the same smell, despite never having experienced the original conditioning. The mechanism appears to involve changes in the receptor neurons in the offspring's noses, with associated methylation changes in the relevant olfactory genes.
This is genuinely interesting. It is also, as the authors themselves emphasized, a phenomenon at the level of sensory tuning, not autobiographical memory. The grand-offspring mice are not remembering that their grandfather was shocked while smelling cherry blossom. They are showing, at the level of their olfactory architecture, a heightened sensitivity to that specific odor — the equivalent of being born with sharper hearing for a particular frequency. The information transmitted is procedural, not narrative.
The distance between "heightened olfactory sensitivity to a specific odor" and "I remember my grandfather's specific experience of being shocked" is approximately the same distance as between "your immune system inherited certain antibody profiles" and "you remember the diseases your grandparents had." In both cases, the inheritance is real, the mechanism is partially understood, and the information transmitted is at the level of physiological tuning, not personal memory.
What the Novels Treat as True
The novels treat as true a thing that is not, by current evidence, true. Specifically, they treat as true the proposition that human carriers can experience fragments of the specific experiences of their ancestors — visions, dreams, body-memory of being in places they have never visited, knowledge of languages they have never learned.
The novels' carriers are not just sensitized at the level of physiological response. They are, in some technically specifiable but biologically unproven way, receivers of information that was encoded into their bloodline by ancestors who deliberately encoded it.
The biological substrate for this kind of inheritance does not exist in any organism we currently understand. The information density required would be orders of magnitude greater than what DNA methylation can carry. The error-correction would have to be more sophisticated than any biological signaling system we have characterized. The retrieval mechanism — how a person would consciously access information transmitted at the molecular level — has no known analog in neuroscience.
If genetic memory worked the way the novels say it does, our species would be a wildly different thing than it is. We would not have spent thousands of years inventing writing, libraries, archives, and oral traditions, because we would not have needed them. The fact that we have spent enormous cultural effort developing external memory systems is, by itself, strong evidence that we cannot reliably transmit internal memories across generations.
The fiction does not pretend otherwise. It is fiction.
Why I Built the Series on the Gap
The series asks a particular kind of speculative question. Not "is this true?" but "if this one impossible thing were true, what would follow?"
Specifically: if a small subset of the human population could carry specific information across generations in a biological medium, what kind of organizations would those carriers form? What kind of competing organizations would emerge to either exploit them or destroy them? How would those organizations operate across centuries? What would the historical record actually look like, if you re-read it through the lens of two networks running such an operation continuously since the Bronze Age?
This is what the series is doing. It is taking one impossible thing — heritable narrative-level memory — and then being rigorous about the consequences. The Bronze Age collapse from this angle, the Black Death from this angle, the late Roman world from this angle, the Templar period from this angle, the Conquest of Mexico from this angle. The same dynamics, the same pattern, run through ten different historical settings.
The historical settings themselves are not impossible. The Bronze Age collapse really happened. The Black Death really happened. Augustine really wrote De Civitate Dei. The Templars really excavated under the Temple Mount. The conquest of Mexico really happened, and the population collapse that followed was real. The eugenics movement of the early twentieth century really existed and really did write the textual basis for the Nazi sterilization program. The CRISPR work being done today is real.
What is impossible is the medium of inheritance that the series uses to thread these real events into a single continuous story. The medium does not exist. The events do. The argument I am making with the series — and I think this is the kind of argument fiction is uniquely good at making — is that the pattern of the events themselves is the thing that matters, and that the pattern is visible regardless of whether the supernatural medium of inheritance is real.
If you remove genetic memory from the series, you still have a record of human civilizations rising and collapsing along identifiable structural lines. You still have networks of people preserving knowledge across collapse events. You still have other networks weaponizing the same knowledge against the populations it could save. You still have the basic political and ethical question the series exists to dramatize: what do you do, what do you owe, what does it cost you, to act on a pattern that most of the people around you cannot see?
The genetic-memory premise is what makes the dramatization work as a thriller. It gives me characters who feel the pattern in their bodies rather than just intellectually recognizing it. It gives me a continuous cast across thirty-two hundred years. It gives me, frankly, the conditions under which the series can be the kind of book people read on planes, instead of the kind of book they read in a graduate seminar.
But the pattern itself — the recurring structure of civilizational collapse, the recurring pattern of who survives it and who does not, the recurring question of what knowledge is worth preserving and at what cost — that is real. The thing the carriers carry is not a literal description of how human inheritance works. It is a dramatized version of how historical memory works, and of what is at stake when that memory is allowed to lapse.
The science of epigenetics is interesting. The fiction of genetic memory is more interesting, because it is doing different work. The fiction is asking what would be true if certain kinds of historical memory could be made non-optional. Reading the series with that question in mind, I think, is the best way to read it.
I do not believe in genetic memory in the way the novels portray. I believe in the pattern the novels are using genetic memory to illuminate. The pattern is real. The medium is fiction. The work, I hope, is honest about which is which.
If you want to start: Book 1, The Aethelred Cipher, is set in 1347 — the year the Black Death arrives in Europe — and centers on a scribe named Thomas of Eltville who inherits an iron key from his dying mentor and discovers, very quickly, what the key actually unlocks.