One of my favorite scenes in the movie Forrest Gump is when father meets son for the first time and sits down on the floor with him to watch Sesame Street. They tilt their heads to the left in unison, as proof of their shared genes. We might think of this as learned behavior, but how can this be if they only just met?
As it turns out, this sweet cinematic moment actually has a foundation in some fascinating science. The rules of genetic inheritance dictate that your DNA gets passed along to your children. But scientists have begun to realize that genetic inheritance may be more complicated than that. In addition to inheriting your dad's blue eyes or your mom's height, you could inherit a behavior, fear or tendency that your mom or dad experienced or learned.
So if you wonder why you feel like you've turned into your mom, you're not alone. Research has shown that it's possible for environmental information to be inherited biologically through chemical changes that occur in DNA, but don't actually alter the genetic sequence itself.
Every cell has a genetic code, and according to the information it holds, proteins are produced to become certain types of cells like skin, organ or muscle. Chemical switches, called epigenetic tags, are attached to your DNA and turn on or off aspects of your genes, depending on events in your environment. These activated genes and how they are expressed can be passed along to future generations, meaning your kids could inherit a trait that you learned through experience.
To demonstrate this, researchers Dr. Ken Ressler and Dr. Brian Dias from the psychiatry department at Emory University's School of Medicine conditioned male mice to fear the scent of cherry blossoms by giving them an electric shock every time they were exposed to it. This activated certain epigenetic tags on a gene in their DNA, and over time, the "switched on" genes made extra neurons in their noses and in the smell-processing center of their brains, greatly increasing their sensitivity to the scent. The activated DNA in the sperm cells of these mice passed along the memory of this experience to their pups, and then to their grandpups. And even though these descendents had never been exposed to the scent or shock, they still reacted with fear when they smelled cherry blossoms.
Mice that had never physically met the parent who was afraid of cherry blossoms still somehow received the genetic impulse for that same fear.
Although, theoretically, the fear of cherry blossom scent could be nurtured directly from the parent mice to their offspring, the pups naturally exhibited the same behavior and fears, generation after generation, even when they had been fathered through the use of artificial insemination. "Our results allow us to appreciate how the experiences of a parent, before even conceiving offspring, markedly influence both structure and function in the nervous system of subsequent generations," stated Dias. This shows just how possible it is for a behavioral trait of your parent to show up in you (and now you might be noticing it in your own kiddo).
Evolutionarily, this doesn't just happen for our entertainment—Mother Nature always has a reason.
Scientists suggest that this biological transmission of memory from the brain into the genome might be a form of biological forward-planning. By adapting to changing environmental and emotional conditions experienced by parents, genes that are activated and passed along better prepare offspring for the environment they are born into. Inheriting the modified gene from the parent prepares the offspring and later generations to survive in their environment and reproduce.
Bottom line: So, that endearing quirk you share with a parent and have passed along to your own kid might have been a survival mechanism inherited directly from your parents, grandparents and many more generations long ago.
Editor's note: A growing body of research indicates that the racism that Black parents experience, and the attendant stress and trauma, causes the same type of genetic rewiring and has been shown to result in inherited health conditions in generations of Black children. For information, please see these resources: