They say that long distances often help revive romance in a relationship, as lovers can't stand the stress of being parted. Now, the notion has been backed by a scientific study, which suggests that grief is nature's way of keeping couples together.
While working with one of nature's only monogamous mammals, the prairie vole, as a model for human attachment, Larry Young from the Emory University School of Medicine in Georgia and Oliver Bosch from the University of Regensburg, Germany, examined the role of stress, which is plays a significant role in the grieving process.
In the study, the researchers paired 18 male voles with females and 20 males with males for five days, enough time for male and female to mate and form an enduring attachment to each other.
The researchers then separated half of each group from its partner and assessed their "mental state".
They found that males that were separated from their female partner displayed behaviour reminiscent of depression and anxiety in humans.
They spent more time floating rather than swimming when dunked in water and struggled for less time when held upside down by the tail, compared with those voles that had been separated from another male.
In vole terms, this means that they showed less will to fight against stressful situations.
The bonded voles also had double the level of the stress hormone corticosterone in their blood, suggesting that CRF, the brain peptide that regulates the stress response, has a role to play in the grieving process.
Young said that the effects seen in the study are very different from those of isolation.
"When the animals lose their bonded partner, the CRF system becomes overactive. In nature this can be a good thing because this stress response makes them seek out their partner again, helping to maintain a stable relationship," New Scientist quoted Young, as saying.
He speculates that if this overactivity lasts for a long period of time then that may lead to behaviours like depression.
"What we are tapping into here is the flip side of the attachment bond. Pleasure sensors of the brain are activated when couples are together but there is another mechanism involved with the stress of being parted," Young said.
Katherine Shear, a psychiatrist from Columbia University, told New Scientist: "Currently we have no effective medication for people who are struggling with prolonged periods of debilitating grief. This work does provide early promise of developing such an approach."
The study is published in the journal Neuropsychopharmacology.