This is hidden brain.
I'm Shankar Vedantam.
People in romantic relationships often share things in common.
A love of the same sports team, maybe the same religion, sometimes a common profession.
But for some couples, the similarities go further.
The girl that I am dating now.
We have the same birthday, which is kind of cool.
My fiance, Israel, and I have the same birthday, which is something we discovered.
On our second date.
You could say this isn't so surprising.
There are lots of people in the world, and sooner or later, some people are going to get together with others who happen to have the same birthday.
But there's evidence this may be more than just a coincidence.
Having a common birthday seems to actually draw people closer to one another.
When I first went to a new hairstylist, we found out that we had the same birthday, and we called each other birthday twins.
And I wound up going to that hairstylist for years, even after she switched salons, even after we moved, I would drive 40 minutes to go get my hair cut by her.
Some people see so much significance in shared birthdays, or even shared numbers in two birthdays, that they select dates for important events based on those patterns.
My birthday is August 2, and my husband Blake's birthday is August 9, and we got married on August 29.
My wife and I share the same birthday, July 6, and we are also married on that day.
My birthday is October 27, and with my first husband, his birthday was September 27, and we had the opportunity to get married on August 27.
It was a no brainer.