This is Hidden Brain, I'm Shankar Vedantam.

No matter how many you've been to,

it's hard to shake the contagious optimism of weddings,

couples vow to love one another in sickness and in health, for richer, for poorer.

Family members dab tiers from their eyes,

agreeing that these two people are meant to be together forever.

But so many marriages become unhappy, some dissolve, some end in divorce,

and even the successful ones aren't without challenges.

No one would deny that long-term relationships are hard,

and in fact, there's evidence they're getting harder.

Why is that?

This week on Hidden Brain, we'll take a closer look at the history of marriage.

Most of what we think of as traditional marriage was not traditional at all,

but a rather recent invention.

We'll also explore the radically higher expectations we have for marriage today.

Lots of people argue that having these high expectations is problematic,

and it's harming the institution of marriage.

And frankly, among the people who used to argue that is myself.

And we'll discuss ways to improve our love lives,

sometimes by asking more of our partners and of ourselves, sometimes by asking less.

To understand marriage today, we thought it best to go back to a time and place

when marriage was very different.

...