A new study suggests that certain fears can be passed on through generations. Researchers linked it to the “scent of fear.”

Researchers Kerry Ressler and Brian Dias from Emory University in Atlanta, Georgia studied a group of mice to find out if it is really possible for the next generations to inherit the fears that their ancestors have. They believe that it may yield similar results to humans.

It is already established that biological information can be transmitted across generations through the genetic sequence in DNAs. Additionally, to enable life forms to adapt in inevitable dynamic processes, DNA mutations take place – which usually happens gradually over generations.

Some studies, on the other hand, say that biology is greatly influenced by environmental factors through “epigenetic” modifications that change the expression of genes, but not their actual nucleotide make-up. However, though epigenetic modifications are considered vital for developmental processes and the inactivation of one X-chromosome in females, their contribution in the behavioral inheritance is still controversial.

The researchers focused on studying the epigenetic inheritance by using laboratory mice guided to fear the smell of acetophenone, a chemical that smells like almonds and cherries.

They let the scent of the chemical linger in a small chamber, while giving male mice electric shocks with low voltage. As a favorable result, the male mice then started to associate the scent with pain, quivering in the presence of the chemical scent.

Their offspring, in spite of not knowing anything about the scent, displayed sensitivity upon smelling acetophenone. They even quivered more than the descendants of mice that had been trained to be frightened by a different scent or those who hadn’t gone through anything.

The same reaction was observed on the mice’s third generation – their “grandchildren.” The researchers even performed an in vitro fertilization using sperm from the male mice trained to the chemical for comparison and similar reactions were noted.

A similar experimentation was performed using female mice and the same thing happened.

These reactions were linked to changes to the brain structures that process odors.

The study claims that the male and female mice and their offspring and grandchildren, in comparison with control mice and their descendants, had more neurons that generate receptor protein that detects the chemical scent.

They also found out that those receptors receiving signals from the acetophenone-detecting neurons and transmitting smell signals to the brain were also bigger.

The researchers explained that a reversible chemical alteration to DNA that normally obstructs transcription of a genetic material without changing its sequence, called DNA Methylation, describes the inherited effect.

This study was published in the Dec. 1 issue of Nature Neuroscience.