Brad and Jen split because of 'clashing chemicals'
Brad Pitt and Jennifer Aniston were never right together because of their clashing chemicals, a scientist claimed.
On the other hand, the right biological match has ensured a blossoming relationship between the Hollywood heart throb and Angelina Jolie.
American anthropologist Dr Helen Fisher believes the fortunes of love depend on just four chemicals in the body.
They decide whether a person is an Explorer, Builder, Negotiator or Director - or a mixture of different elements.
Explorers, like Pitt and Jolie, are mostly influenced by the brain chemical dopamine, and are novelty-seeking, risk-taking and spontaneous.
On the other hand, Aniston is a "calm, conscientious, loyal and cautious" Builder dominated by serotonin in the brain.
Explorers are chemically matched to other Explorers, but not to Builders, according to Dr Fisher.
This could explain why Pitt's marriage to Aniston broke down while his relationship with actress Jolie goes from strength to strength.
For Negotiators, the female hormone oestrogen takes the lead, even in men who belong to this group, says Dr Fisher. They are said to be imaginative, intuitive, compassionate, and blessed with good people skills.
Directors, in contrast, are ruled by the male hormone testosterone. These individuals, who include women as well as men, tend to be direct, decisive, competitive and often musical.
While Explorers are attracted to Explorers and Builders to other Builders, Directors and Negotiators are better with each other than someone sharing the same personality traits, it is claimed.
Gordon and Sarah Brown are examples of Builders who support each other, while David and Samantha Cameron are both Explorers, as are US President Barack Obama and his wife Michelle.
Tom Cruise, a Director, is said to be well matched to Katie Holmes, a Negotiator - the same combination as Bill and Hilary Clinton.
Dr Fisher, from Rutgers University in New Jersey, studied the the personality traits of more than 28,000 members of the internet dating site Match.com.
The different chemicals are known to be associated with different characteristics and behaviours in people.
"The reasons why we love are incredibly complex, but it is possible to scientifically understand why people partner better with certain types," said Dr Fisher.
Participants in the study answered a series of detailed questions after a first date to see if their chemically-driven characteristics kindled a romantic spark.
Dr Fisher found that her theory was partly born out by the relative length of people's ring and index fingers, which is influenced by testosterone and oestrogen exposure in the womb.
She is now carrying out a more thorough investigation of 200 individuals, comparing their personality traits with a wide range of chemicals in their blood, saliva and urine.
"I'm looking at scales rather than brackets, because we all have all four of these chemicals but are more influenced by certain ones," she said.
"My hypothesis was that we would be drawn to our opposites to give a genetically stronger mix, but I was half right and half wrong. High oestrogen and high testosterone types seem to go together, but high serotonin people go for others like themselves and the same is true for dopamine."
Match.com has developed a personality test for its members based on the findings which has so far been taken by seven million people in 39 countries.
Dr Fisher describes her research in her book Why Him? Why Her? published on March 19 by Oneworld Publications.
Her findings have also been submitted to a well known scientific journal.