Scientists say they've found a gene which could be responsible for whether we're lucky in love or doomed to be forever alone.
But even if you don't have it, all is not lost - it could just be a matter of clicking with someone who does.
"Given the importance of close relationships for human survival, many have thought that humans evolved as a species to have a proclivity to form enduring pair bonds," psychologist Jennifer Bartz of Canada's McGill University told The AM Show on Friday.
"Research in non-human animals has highlighted the important role of the neuropeptide oxytocin in both mother-infant and adult-adult pair bonds. We wanted to look at the role of oxytocin in romantic bonding... in daily life."
Neuro-peptides are a molecule which allows different parts of the brain and nervous system to talk to each other.
Dr Bartz' team got 111 straight couples to record their interactions for 20 days - how they felt, and how they think their partner felt. Then the researchers took a look at the participants' genes, finding one in particular appeared to be linked to "higher communal behaviour".
"They perceived their partner to behave more communally, they experienced less negative affect and felt less insecurity in their daily interactions with their partner," Dr Bartz said.
The gene, CD38, comes in three different types - AA, CC and AC. Those with the CC version were not only more likely to "to see their partner as behaving communally and they experienced fewer negative feelings, such as worry, frustration or anger than AA or AC genotypes", according to the study, published in journal Springer Nature.
Dr Bartz said somewhere between 40 and 50 percent of us have the CC variant. In couples where only one person had it, it appeared their partner - though lacking - was influenced somewhat, reporting higher levels of relationship quality than in couples where both were without.
But with some couples succeeding despite both lacking the gene, Dr Bartz said it raises interesting questions around how much of our behaviour is determined by our genes.
"While communal behaviour may be more intuitive or instinctive for individuals with the CC variant, it's not impossible for others who are not blessed with this variant to make a concerted effort to display that kind of behaviour in our interactions.
"We can remind ourselves that smiling to another person, displaying affection in words or gestures usually makes people feel good and it usually has really positive outcomes for our relationships in general."
