Do you have a fear of spiders? Maybe snakes? It could be your ancestors trying to tell you something. Recent studies have provided evidence that memories of fear are one of many things our forebearers pass down to us through our DNA.

A 2013 study from Emory University found that mice trained to fear a specific odor would pass their emotions on to their offspring and future generations. Scientists applied electric shocks to mice as they exposed them to the smell of cherry blossoms. The mice then bred, and both the children and grandchildren of the affected rodents demonstrated a fear of cherry blossoms the first time they smelled them.

“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,” Dr. Brian Dias of the Emory University department of psychiatry said to the Daily Telegraph. “Such a phenomenon may contribute to the etiology and potential intergenerational transmission of risk for neuropsychiatric disorders such as phobias, anxiety and post-traumatic stress disorder.”

The study went beyond just observing a fear reaction. Scientists actually looked at the brains of the animals and found physical changes in the areas that process odors, and also found a marker on the odor gene of the mouse DNA.

The experiment worked even when the researchers used artificial insemination in place of allowing the mice to breed naturally. The scientists still aren’t sure how the fear imprint makes it into the sperm — whether the smell itself passes through the blood, or the brain processes the odor and sends its own signal.

“It is high time public health researchers took human transgenerational responses seriously,” Prof Marcus Pembrey, from University College London said to the BBC. “I suspect we will not understand the rise in neuropsychiatric disorders or obesity, diabetes and metabolic disruptions generally without taking a multigenerational approach.”

Humans have long sought to understand memory and heredity, nature vs. nurture and how much information parents actually transmit to their children. The nature study is another step toward answering our questions about exactly what, and how much of our forebearers’ experiences get passed down through DNA.

Primordial Fears

There is already a growing body of research about how humans and other animals inherit fear from their ancestors. A study published in the Proceedings of the National Academy of Sciences in 2013 found that primates’ brains are uniquely tuned to recognize snakes, suggesting that we gained an innate fear of the reptiles over the course of our evolutionary development. A 2011 study in Current Directions in Psychological Science found that human infants aren’t necessarily afraid of snakes from birth, but they learn to fear them more quickly than they learn to fear other more innocuous stimuli like flowers and rabbits.

“What we’re suggesting is that we have these biases to detect things like snakes and spiders really quickly, and to associate them with things that are yucky or bad, like a fearful voice,” study co-author Vanessa LoBue of Rutgers University said in a press release. The research built on previous work by LoBue and her team that showed that people were able to identify snakes and spiders more quickly than other animals and objects. There’s even evidence that primates actually developed large brains and keen eyesight as a defense measure to avoid falling prey to snakes.

Another study found that unborn crickets whose mothers were stalked by wolf spiders showed more fear of spiders after they were born than control crickets — not to mention a higher survival rate. At this point there’s little doubt that fear gets passed down through the generations — now we’re learning about how.

Rewriting The DNA

Fear isn’t the only thing that gets imprinted in our genes. Recent breakthroughs have made big strides in understanding epigenetics — how our DNA gets changed by environmental factors. A study published in 2013 revealed details about how certain aspects of DNA can be turned on or turned off, and therefore passed on to offspring or not. A report last year found that Crohn’s disease can cause epigenetic changes in people who suffer from it. And scientists were able to edit the DNA of mice to cure them of an inheritable liver disease — with hope that the same process would work in humans.

Other researchers are working on how to encode DNA with specific information. A study led by synthetic biologist Timothy Lu of MIT and published in Science in 2014 found a way to rewrite living DNA in a cell and watch as the altered information was transferred to new cells. The researchers changed cells to make them sense light and react to other stimuli. Next, they hope to use the technology to make a recording of the cell’s environment for study, such as placing the cells in water for a week and then testing them for toxins.

Other scientists have managed to etch the equivalent of a megabyte worth of data onto DNA, and then read it back. Both studies are more geared toward gathering and storing information, but the more we learn about how to change DNA, the possibility looms that we could learn how memories are implanted — and someday even artificially create hereditary memories, if scientific interest and ethics allowed such an outcome.

Beyond The Physical Realm

The idea of memories being written into DNA could provoke speculation about phenomenon like visions of past lives, although it might be a leap to go from a reaction to odor to the recall of specific and discrete memories.

Polish Professor of Pedogogy Andrzej Szyszko-Bohusz has worked since the 1960s to promote a theory of genetic immortality in which parental consciousness is transmitted to children along with DNA and other hereditary information. More recently, University of Virginia (UVA) professor Jim Tucker hypothesizes that consciousness needs no physical binding at all to pass on. Tucker, who studies children who have memories of past lives, claims that quantum physics suggests that our physical world is created by our consciousness. Therefore, consciousness doesn’t need the world, let alone a brain, to exist, and could simply affix itself to a new brain once it passes out of a dying one.

“I understand the leap it takes to conclude there is something beyond what we can see and touch,” Tucker said to UVA Magazine. “But there is this evidence here that needs to be accounted for, and when we look at these cases carefully, some sort of carry-over of memories often makes the most sense.”

He calls it the science of reincarnation. Whether he is on the right track, or we discover that memories are passed down by DNA all along, or there is some other mechanism we don’t know about yet, is still to be determined.