Monarch butterflies travel over 3 000 miles from Canada to Mexico each year. It takes three generations to make the full trip, and no single butterfly ever makes the return journey. How do they reach the same spot each year? By instinct? Is this an example of genetic memory passed down from parent to offspring?
Most of our genetic makeup (that determines hair colour, complexion, and so on) comes from DNA passed down by our ancestors. However, our environment also has a significant impact: While it does not condition our DNA sequence, it can affect how our genes are expressed, which, for instance, could explain why identical twins are not actually identical. This “epigenetic” information is susceptible to change throughout our lifetime due to lifestyle, environment or disease.
According to recent research, environmental information could be passed down genetically from parent to offspring. This does not refer to a parent’s teachings, but rather a “factory load” of some environmental memory that determines which genes are expressed. If you have ever wondered why you have an “irrational” fear of spiders or snakes, this may be a survival mechanism inherited from your distant ancestors who were more exposed to these dangers. The more fearful our ancestors were, the greater their chances of survival and of transmitting these genes and environmental memory. Our surroundings have changed faster than we have evolved as a species, so while we still have these prehistoric survival instincts, most of us are never confronted with these dangers.
“Memory is the fourth dimension to any landscape” – Janet Fitch
Research from the Emory University School of Medicine in Atlanta provides evidence for this passing-on of genetic memories. Mice were trained to associate the smell of cherry blossom to an electric shock, so they feared and avoided areas with that odour. The offspring of these mice would also avoid areas with the scent, even though they were never exposed to the electric shocks. The researchers found that the part of the genome that determines sensitivity to that scent was more active in the mice’s sperm, and found differences in brain structure for both the offspring and the parent generation. The fear of the scent was not “taught” by the parents, as the same results were found when in vitro conception was used (e.g. parent and offspring never meet), but genetically transmitted.
Meanwhile, the European Molecular Biology Organization has shown that environmental changes can affect up to 14 generations of offspring in a species of worms. The experiment involved implanting a gene that, when activated, makes the worms glow under UV light (this occurs at a temperature of 25°C but not at 20°C). The first result of this study is that the worms continued to glow when moved from 25°C to 20°C, meaning that they retained some “environmental memory” from their time in the warm climate. The second and most interesting result is that the offspring of these worms glowed too (for up to 14 generations when the five previous generations had lived only in the warm climate). They retained a memory of the warmer environment and their fluorescent gene was active accordingly, despite never having been exposed to 25°C. This memory transmission “may be biological forward planning” by giving an indication of what the environment is likely to be in the future and thus increasing chances of survival, according to Adam Klosin, one of the authors of the study.
What does this mean for us?
At this point it is important to caveat these studies’ potential application to humans. Due to longer life spans and the absence of laboratory conditions, it is extremely difficult to replicate these results for humans, but the possibility of genetic memory being transmitted between generations does exist. According to recent studies, human offspring can possess a different epigenetic makeup due to traumatic events that their ancestors lived through. For instance, after the Dutch famine of 1944-45, the children and grandchildren of women who survived had increased glucose intolerance compared to the control group. Another study found that the offspring of Holocaust survivors had less hormone cortisol (which helps the body bounce back after a trauma), which could lead to a predisposition to anxiety disorders.
Understanding how genetic memory is transmitted would be a significant step in treating phobias, as well as in preventing and curing genetic diseases such as Alzheimer’s or cancer with increasingly sophisticated gene manipulation techniques. More broadly speaking, the transmission of epigenetic information means that the effects of a bad environment harm not only the current generation, but also the offspring, making the fight against pollution and polluted environments even more vital.
by Tristan Salmon