It is well known that DNA is the construction manual of life, DNA sequences lead to amino acids which are built into proteins which build the cells and enzymes needed for an organism to grow. Changing even one letter of DNA can have profound effects on an organism, sickle cell disorder being a good example in humans.
But what if more than just structure could be passed on to your offspring through your DNA? Controversial new research suggests that learned behaviours such as fears may be able to be inherited via a mechanism called epigenetics, a form of DNA modification that doesn’t affect the code but instead adds a methyl molecule to certain DNA sites that can affect how often the DNA is transcribed and translated into proteins.
In order to study this phenomenon researchers from the university of Emory in Atlanta, Georgia exposed mice to a molecule called acetophenone which has an odour similar to cherries, every time the mice were exposed the smell they received electric shocks, becoming fearful of the smell and eventually reacting negatively with just the presence of acetophenone without the shocks.
Interestingly, even though the offspring of those mice had never encountered acetophenone before, they reacted with fear, shuddering more vigorously than control mice who had been made fearful of a different odour, or who had never been conditioned to experience fear. Even more remarkable is the fact that the 3rd generation of mice, or the grandchildren to the original conditioned mice also appeared to have inherited this reaction to the acetophenone. Mice grown via in vitro fertilisation from surrogate mothers also experienced the same unconditioned fear.
However the controversy stems from the fact that the mechanism which may bring about this inherited fear is not yet certain. In the conditioned mice the DNA of the sperm cells had less methylation marks on the acetophenone receptor gene which the researchers speculate may lead to more of the receptors being present in subsequent generations.
Exactly how this reduction of methylation may occur is the sperm, a completely unrelated system to the olfactory and neural tissue associated with pain and fear is unknown however. Further Timothy Bestor of Columbia University is skeptical that the acetophenone gene has the required sites to be affected by methylation.
The validity of the research is further complicated by the fact that studying a similar effect in humans is difficult due to ethical concerns and the availability of subjects. One such area the researchers suspect certain environmental neurological traits may be inherited is in the case of drug addiction and psychiatric illness seem to be passed on between parents and their children in low socioeconomic areas.
I would be tempted to contend however that this may simply be a case of increased probability of learning these behaviours because of the increased exposure that comes with low socioeconomic status. Health care is unfortunately also lacking in these sorts of environments which could account for the apparent inheritance of psychiatric disorders.
One way to test this would be in cases where children born of drug addicts are adopted, if the adopted children are raised in a higher socioeconomic family, an epigenetic inheritance of the drug addiction would make these children more likely than children from non drug addicted parents to develop an addiction if they are both raised in an equivalent family setting.
If a molecular mechanism can be found this new research may lead the way eventually to studying how behaviours are passed between generations, possibly with ways to treat undesirable behaviours. It may open the door to studying other traits that so far have not been considered to be inherited by epigenetic means.