When we think of memory, we usually think of things we have personally experienced: a face, a place, a story, a skill we learned.
But the body also carries forms of information that existed long before personal memory began.
DNA contains biological instructions passed down across generations. These instructions help shape the body, guide the development of the nervous system, regulate cellular activity, and contribute to many traits we are born with. A single copy of the human genome contains roughly three billion base pairs, an enormous amount of information packed into a remarkably small biological structure.
If we use the word “memory” in a broader sense, DNA can be understood as one way life preserves its past: traits and instructions that have persisted long enough to be carried forward into another generation.
This is very different from remembering an afternoon, a face, or a chapter of one’s life. It belongs to another kind of biological continuity.
DNA does not contain a complete human being waiting to be unpacked like a finished blueprint.
It carries genetic information, while the way that information is expressed depends on many other processes throughout cells and the body. Genes can become more or less active depending on cell type, stage of development, and biological environment. Epigenetic processes are part of this regulation.
The same DNA can therefore function very differently across different cells, stages of life, and biological conditions.
This is where comparing DNA to a hard drive becomes both useful and misleading.
A hard drive stores data so that it can later be retrieved in nearly the same form. DNA operates inside a living system that is constantly developing, responding, and regulating itself.
Biology also uses the word “memory” outside the context of remembering with the brain.
One example is epigenetic memory, which describes the persistence of certain patterns of gene activity across cell divisions even when the underlying DNA sequence remains unchanged. A cell can retain traces of an earlier state and pass aspects of that state on to daughter cells.
Here, “memory” refers to something being preserved over time.
It is different from personal memory, but the common thread is retention: something from the past continues to shape what happens in the present.
In this series, “biological memory” is used in this broader sense to describe information and lasting traces carried through inheritance, development, and lived experience. These do not all arise from the same mechanism and should not be treated as one single type of memory.
The original text that inspired The Ascent of Memory opens with a striking comparison: when synthetic DNA is used for digital data storage, its potential density can reach hundreds of petabytes per gram. A 2017 study using a method known as DNA Fountain achieved a density of roughly 215 petabytes per gram.
That figure refers to DNA used as an engineered medium for storing digital information. It does not mean that one gram of DNA inside the human body contains 215 petabytes of personal memory.
Even so, the comparison points to something worth noticing: life has been using extraordinarily compact structures to carry and transmit information for far longer than humans have been building hard drives.
A genome can be sequenced. Having the sequence in hand, however, does not amount to understanding everything about how a person will develop, respond, or live.
The Human Genome Project completed a near-complete reference sequence of the human genome in 2003. Knowing the long sequence of A, C, G, and T was a major step, but understanding how that sequence operates inside a living human being is a much larger task.
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