Once upon a time, there were two thinkers on the topic of evolution. Charles Darwin argued that mutations occurred constantly and were tested against adaptation, with only those that were advantageous statistically persisting; Jean-Baptiste Lamarck suggested that it was possible for acquired traits to be passed on to the next generation. As it turns out, both were right, to varying degrees.
Genetic memory refers to the ability for memories, or at least traits responding to those memories, to be encoded in the DNA of an organism and passed to its offspring and their offspring. Scientists have found that genetic memory of trauma is passed along to grandchildren, for example:
A study examining the offspring of children displaced during the Second World War revealed they were up to four times more likely to suffer from serious mental health conditions compared to those whose parents stayed at home.
…Its authors say the effect may be partially explained by poor parenting by the evacuees, but they believe it is more probably due to epigenetic alterations – changes to the way genes are expressed – which are then inherited.
A previous smaller study found that Holocaust survivors had higher levels of methyl groups associated with a gene that influences the production of the stress hormone cortisol.
This may be because memories change brain structure and this structural alteration is passed on through epigenetics to the offspring:
A Nature Neuroscience study shows mice trained to avoid a smell passed their aversion on to their “grandchildren”.
…The animals were trained to fear a smell similar to cherry blossom…[Scientists] showed a section of DNA responsible for sensitivity to the cherry blossom scent was made more active in the mice’s sperm.
Both the mice’s offspring, and their offspring, were “extremely sensitive” to cherry blossom and would avoid the scent, despite never having experienced it in their lives.
Changes in brain structure were also found.
Interestingly, this research proves Robert A. Heinlein correct in one thing. Characters in his novels took RNA pills in order to obtain skills, such as martial arts or playing a piano. As it turns out, a certain type of RNA plays a role in programming this brain structure:
Researchers have been preoccupied with how the effects of stress, trauma, and other environmental exposures are passed from one generation to the next for years. Small RNA molecules — short sequences of RNA that regulate the expression of genes — are among the key factors involved in mediating this kind of inheritance. Dr. Rechavi and his team had previously identified a “small RNA inheritance” mechanism through which RNA molecules produced a response to the needs of specific cells and how they were regulated between generations.
“We previously showed that worms inherited small RNAs following the starvation and viral infections of their parents. These small RNAs helped prepare their offspring for similar hardships,” Dr. Rechavi said. “We also identified a mechanism that amplified heritable small RNAs across generations, so the response was not diluted. We found that enzymes called RdRPs are required for re-creating new small RNAs to keep the response going in subsequent generations.”
These changes reflect an elemental need for non-verbal organisms to pass along information about threats in the environment, and suggest an evolutionary advantage to language, which can more quickly transmit social capital about complex things. One study found that the offspring of crickets who were stalked by wolf spiders were more accurate at recognizing and evading spiders. In more complex organisms, the fear of dangerous animals is not passed along as behavior, but as a tendency to more quickly distinguish that type of animal — in this case, snakes — from others as a source of danger. According to another worm study, changes may persist for as many as fourteen generations, enshrining that knowledge for as long as it is relevant.
For humans, this knowledge brings many interesting implications. We may have genetic memory of culture, and hard-wired tendencies to view certain species, groups, or activities as undesirable because of the experiences of our ancestors. We may also be able to learn things today that future generations can then take advantage of, in addition to the social capital we pass on through language.