This is hidden brain.
I'm Shankar Vedanta.
Look up at the sky in most places in the world and you will see flocks of birds.
Look carefully and you'll see these flocks are usually made up of the same kind of birds.
Pigeons flap around with other pigeons, crows with crows.
Starlings congregate with, well, lots and lots of other starlings.
Somewhere along the way, someone coined a memorable phrase.
Birds of a feather flock together.
Sociologists have noticed that this phenomenon is not restricted to birds.
Humans tend to do the same thing, except because we are complex creatures.
The things that draw us together are not just physical similarities, but cultural constructions such as social class, shared interests, and common cuisines.
We think nothing of the fact that music lovers hang out with other music lovers, or that book readers congregate in book clubs and that gardeners form their own societies.
The Internet has made it possible for people with all manner of niche interests to discover others who are exactly like them.
When we do think about this at all, we usually say, it's a wonderful thing.
Well, it is and it isn't.
This week on hidden brain, the unintended consequences of enjoying the company of others who are just like us.
The next time you attend a wedding, take a close look at the couples around you.
The couple getting married, sure, but all the other couples, too.
How many couples do you think have both members vote for the same political party, or belong to the same race, or speak the same language?
The answer is obvious.