Children sometimes come out with the most significant questions, and in their innocence, often assume we have the answer. Usually, we do not. On the few lucky occasions, however, we may, in fact, know how to answer. I recall having a conversation with a small child as we finished reading “Charlottes Web.” She turned to me and asked, “How do the baby spiders know how to make webs if Charlotte isn’t alive to show them?”
How does a newly hatched Orb Weaver spiderling know how to weave a perfect web, characteristic of their species, climate, and prey, without having been taught? For that matter, how does a caterpillar know when it is time to pupate to become a butterfly? Why does my cat push things off the table, without ever being taught to perform this rather annoying pastime she is so fond of?
Psychologists term such behavior “instinctive,” and surmise that it is governed by traits that are passed down over generations that help the organism survive and reproduce. But this doesn’t help us understand precisely how these instinctive behaviors work. While researchers today have a pretty good handle on how memories are formed (visual, auditory, or tactile perceptions stored in clusters of hundreds of thousands of neurons that form a memory circuit), can this understanding help us where instincts are concerned?
Instinctive behavior is said to be rigid, often inflexible (think migration), while learned behavior is flexible, and is dependent upon the individual and how the action is reinforced. Can understanding memory and behavior really help us understand instinct? It will if we accept that both instinct and learned behavior is adaptable. Robbins fly south for the winter, but as the climate warms, we have flocks of Robins that winter over. Does this mean that instinct can be overwritten, or relearned? Let us consider the reason that organisms have instincts.
Instincts could be thought of as preset behaviors designed by nature to avoid risks associated with survival by instilling the behavior of adults (like baby spiders knowing how to spin webs) from embryonic development. Mother spiders, unlike most human mothers, are not known to be particularly attentive, so this adult behavior is a necessary instinct for survival. These features are genetic and evolved along with the organism to ensure survival, at least until reproduction. While it’s easy enough to understand that survival instincts are the proven variations of natural selection, is it possible that behaviors, learned behaviors can be passed down genetically? Can these behaviors be inherited as well as learned?
The idea of memory stored in DNA to be passed down to offspring might not be as crazy as it sounds, and we have identified some of the possible mechanisms that would allow for learned behavior to be inherited. Researchers believe it may be closely associated with temperament. While all kittens are born kittens, they have widely different personalities. Just has two spiders from the same egg may create the same web, but behave somewhat differently.
If true, this means that memories, including collected memories of the population, may be passed down through genetics that allows descendants to inherit experiences. And while psychologists have long suspected that memories in the form of learned experiences can be passed down genetically, this has remained a largely unproven hypothesis. Recently, researchers at Emory University School of Medicine have determined that mice pass on learned information to subsequent generations. In this study, mice were taught to fear the smell of cherry blossoms, and it appears that this information is inherited through chemical changes in the DNA. Researchers believe that the results of these tests may explain why some people suffer from irrational phobias that may have been inherited from the personal experiences of their parents, grandparents, etc. And while epigenetics help explain how instructions can be passed down through generations, the environment itself can also create genetic changes. And while the evidence for genetic memory is significant for lower life forms like nematodes, insects, and even mice, when it comes to humans inheriting memories through genetics, there is significantly more research needed. Mainly because social pressures and events in our lives can affect the development of our offspring without changing DNA. Still, there are some accounts not easily explained through learned behavior.
One study showed that the children and grandchildren of women who survived the Dutch famine that occurred in the winter of 1944-1945 had increased glucose intolerance as adults; simply put, they were unable to process normal levels of carbohydrates as well as other children whose parents or grandparents had not endured the famine. Another study found that descendants of Holocaust survivors exhibited a lower level of cortisol, a stress hormone that is involved with the fight-flight survival response.
Regardless, far more is needed before we can fully understand this process. Epigenetics is an exciting field that holds much promise in allowing us to better understand the human condition and how the lives of our ancestors impact us still.