Birth order is a “valid predictor” of who you might end up in a relationship with, according to a leading author.

William Cane believes that the order in which someone is born among their siblings is one of the strongest indicators of personality traits.

On Moncrieff this week, he explained why people of certain birth orders may not be compatible romantically.

“It’s based on research which is very strong,” he said.

“Some of the personality traits in people are so subtle and hidden that people don’t notice them.

“Most scientists have concluded that birth order is a valid predictor of personality.”

Firstborns

He said firstborns often come into conflict with one another.

“It’s known as rank conflict,” he said.

“Two people who are firstborns often tend to both be the leader and both be the director of things, and they should expect to experience conflict.

“It sometimes can be a compatible relationship, but [psychologist] Walter Toman has said that is a narcissistic relationship.

“We’re talking statistically here.”

He added that the majority of US presidents have been firstborn children.

Four siblings. Image via pexels.com

Mr Cane also weighed in on whether firstborns and only children can be in a relationship.

“Certainly, in many cases, particularly if the only child is female, she will do very well with a firstborn boy who has a younger sister,” he said.

“When you have a younger sister or a younger brother, and then there’s also the result when a person has both sisters and brothers who are younger.

“So, the personality picks up differences based on the childhood experiences growing up.”

Age gap

He said the birth order effect is lessened depending on the age gap between siblings.

“When the gap is close, the effect is strong,” he said.

“When the gap gets over seven years, the effect becomes so attenuated that it almost disappears.

“If your sibling is seven or more years distant from you, the effect almost evaporates.

“The most important effects in children are between siblings that are between one to, say, three, four, or five years difference.”

Deviation

Mr Cane said there is another way in which birth order rules can deviate.

“If a person has conflict with their parents that is more than average, and they are the firstborn, they become what [psychologist] Frank Sulloway terms an honorary lastborn,” he said.

“Usually, firstborns are very agreeable, and they toe the line, become religious, and follow in the footsteps of their parents.

“But if there’s a lot of conflict, more than average, they tend to rebel against that pattern.”

He added that he himself fits into these parameters.

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