[cross-posted from our Psychology Today blog]
In the supernatural thriller Memory, written by Bennett Joshua Davlin, Dr. Taylor Briggs, who is the leading expert on memory, examines a patient found nearly dead in the Amazon. While checking on the patient, Taylor is accidentally exposed to a psychedelic drug that unlocks memories of a killer that committed murders many years before Taylor was born. The killer turns out to be his ancestor. Taylor’s memories, despite being of events Taylor never experienced, are very detailed. They contain the point-of-view of his ancestor and the full visual scenario experienced by the killer.
Though the movie is supernatural, it brings up an interesting question. Is it possible to inherit our ancestors’ memories? The answer is not black and white. It depends on what we mean by ‘memory’. The story of the movie is farfetched: there is no evidence or credible scientific theory suggesting that we can inherit specific episodic memories of events that our ancestors experienced. In other words, it’s highly unlikely that you will suddenly remember your great-great-grandfather’s wedding day or your great-great-grandmother’s struggle in childbirth.
But the idea of inherited, or genetic, memory of a different kind has some degree of plausibility. There are many different types of memory. Episodic memory is memory of specific events, such as your memory of your last birthday party. Semantic memory is memory of information that is presented as a fact, for example, the fact that Obama is the current president, that ‘ranarian’ means ‘frog-like’ or that 31 is a prime number. Finally, procedural memory is memory of how to do things, for example, my memory of how to swim or change a light bulb.
It is uncontroversial that procedural memory can be inherited. Babies know how to suck without being taught how to do it. This is a kind of procedural memory, and it is clearly genetic. The central, and much more controversial, question is whether episodic and semantic memory can be inherited.
Semantic memory seems to be the most likely candidate to be, at least partially, genetic. Prominent philosophers, psychologists and linguists throughout history have thought that semantic memory is not always acquired through learning. The great ancient philosopher Plato thought that souls that are instantiated in a human being are part of a Platonic heaven. In the Platonic heaven, the souls acquire Platonic universal ideas (for example, piety, justice, moral goodness). When a soul is instantiated in a newborn, the baby learns these universals by “looking behind” the veil of physical reality and finding the truths in her soul.
Carl Gustav Jung, a Swiss psychotherapist and psychiatrist and the founder of analytical psychology, is well known for his theory of the collective unconscious. The collective unconscious, unlike the personal unconscious, is a type of genetic memory that can be shared by individuals with a common ancestor or history. According to Jung, the collective unconscious consists of implicit beliefs and thoughts had by our ancestors. While we are not aware of the collective unconscious, it can influence how we act. To take a rather mundane example, if our ancestors had a belief that fire was dangerous, this belief can be part of our collective unconscious and influence how we behave when we are near fire.
Jung hit upon his theory of the collective unconscious during psychoanalysis of his patients’ dreams. He believed that the symbolism he found was prominent in his patients’ dreams often bore marks of a specific ancestral history. This type of symbolism is a type of dream event that is difficult to explain by anything in the dreamer's own life.
In modern times, Noam Chomsky, an influential American linguist, is famous for having put forward a theory that has an element of genetic semantic memory at its core. Chomsky argued that human beings are born with a capacity for language acquisition that puts certain constraints on what sorts of human languages are possible. The constraints that limit what sort of grammar a human language can have are also sometimes referred to as a ‘universal grammar’. The universal grammar can be understood as an inherited network of structures that is common to all of us.
How could genetic semantic memory be manifested in the brain? Memories are stored in the brain in the form of neural networks in the cerebral cortex, the brain’s outer layer. The brain deposits specific proteins along the neurons’ synapses that make it more likely for the neurons to communicate in the future. This is also known as ‘long-term potentiation’. While the proteins are normally deposited as a result of learning, it is possible that some of them could be coded for by the genetic code.
But if, indeed, there is such a thing as genetic semantic memory, which part of the human genome codes for it? We don’t really know. What we do know is that we haven’t yet discovered the purpose of many segments of the genetic code. Some of these segments may contain semantic memory information.
There is some evidence that people who are born without one of the senses still have the ability to form visual images that represent the lacking sensory information. For example, people who have been blind from birth sometimes report visual imagery. We cannot confirm that what they are reporting as “visual imagery” really is truly visual. To confirm this we should look at whether there is neural activity in visual areas of the brain in these subjects when they engage in visual imagery. But that will be a project for the future.