In a study published by scientific journal PLoS ONE, the group found that the young of domestic hens exposed to high levels of stress displayed similar behavioral anomalies despite growing up in a stress free environment.
Furthermore, genetic modifications in the young chickens' brains were similar to those developed by their parents as a result of stress.
Per Jensen is keen to stress that the results do not mean that Darwin was wrong.
"But we have seen that an animal population can quickly adjust to new environmental conditions by passing on modified patterns of expression to their young. This was not considered possible in the classical theory of evolution," he said in a statement released by Linköping University.
The researchers observed two groups of chickens, one of which was exposed to a stressful environment. Their daily rhythm was disrupted, making it difficulty for the animals to judge when they were to be fed and when they should sleep. The stressed environment proved seriously detrimental to their learning ability when compared to the other group.
When the researchers studied the young of both groups, they found that the young of stressed hens had the same learning difficulties as their parents. These chickens also grew at a faster rate and were more dominant than the young of the group not exposed to stress.
"What is interesting is that the chickens themselves did not experience any stress. From the moment the egg was laid, they were treated exactly the same as the control animals. The differences must result from the brains of the chickens with stressed parents developing differently," said Per Jensen.
The researchers examined the expression levels of 9,000 genes in one part of the parents' brains to see if a genetic link could be established. They found that these levels fluctuated in the genes of the stressed animals, becoming either more or less active.
The young of the stressed animals displayed the same genetic changes.
According to the researchers, the parent's experiences had altered the function of the genes in the brains of their young, whose behaviour was also affected. This suggests that the behavioural changes were inherited by genetic means.