So a fear of spiders may in fact be an inherited defence mechanism laid down in a families genes by an ancestors’ frightening encounter with an arachnid.

Dr Brian Dias, from the department of psychiatry at Emory University, said: “We have begun to explore an underappreciated influence on adult behaviour – ancestral experience before conception.

“From a translational perspective, 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.

“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.”