If you rely on this too, or hope to, be careful: twins switch personality traits at will.

For example, one of our infant girls would be shy one week while the other was a social butterfly. Just when you thought that was the pattern, they switched and the social standout would cry hysterically with strangers. Go figure.

We’ve seen switching of twin personalities and traits from an early age in all these cases:

So if you want to keep your twins straight, particularly if they are identical, combine multiple data points in identifying each. Combine personality traits and even subtle visual clues to properly identify who is who.

It is fascinating to watch the switcheroo happen. Just keep your eyes open and enjoy the journey.

Twin dad Todd Courtney observed that his identical twin boys would “flip back and forth” in terms of being empowered or following, with “role reversals that happened throughout their childhood”

Jonathan Snowden, father of twin girls, noted that his daughters, Elizabeth and Lucy, do not “stick to, like, one characteristic or act a certain way” but “interchange with each other”. He explained that one day Elizabeth might be the loud and active one, and the next day Lucy would take on that role, as “they just interchange with each other with their personalities.”

Andy Slinger, a father of identical twin boys, observed that his twins’ personalities would switch over time. He noted that as his boys grew up, they “jumped between different personality types”, with one sometimes being the leader and then the other taking on that role.

Personality is about 50% heritable. Extensive twin studies have consistently found that roughly half of the variance in personality traits is attributable to genetics. This is based on comparing identical twins (who share 100% of their genes) to fraternal twins (who share about 50% of their genes). Identical twins are consistently more similar in personality, even when raised apart, which provides strong evidence for the role of genetics.

The remaining half of personality variance is attributed to “non-shared environment.” This refers to unique experiences that one twin has that their twin does not. These are not shared family events, but individual experiences like different friendships, teachers, illnesses, or even a different reaction to the same shared family environment. This is the key factor that causes even identical twins to have distinct personalities.

The post Twins Personalities Switch appeared first on Dad's Guide to Twins.