It’s Valentine’s Day. And here at the Curiosity Desk that means it's also an opportunity to ask a few questions about the holiday that celebrates all things love. Who better to guide us on this quest than Marilyn Yalom? Yalom is a distinguished scholar at Stanford University, and a prolific author who has written extensively about love in books like "The History of the Wife" and her latest, "The Amorous Heart." Plus, the first thing she said when we started our chat was: "I am curious about a lot of things." Perfect!

When it comes to love, there is perhaps no more dominant symbol than the heart. So, for starters, just how did the heart become so strongly linked with love in the first place?

"It happened long, long, long ago," said Yalom. "As far back as the Egyptians, as far back as the ancient Greeks."

For example, in 600 BC, Sappho was scribing lines of poetry that could double nicely today as the chorus of a Taylor Swift song.   

"She’s saying things like, 'Love shook my heart like the wind on the mountain,'" said Yalom.

Yalom says the association was natural. Just as it is for you or me, so it was for the ancients. The sight of a potential lover? A first kiss? An intimate embrace? You can literally feel your heart kick into overdrive.

"Not just the poets, but the philosophers and even the physicians attribute emotion to the heart," said Yalom. "And that goes on for centuries and centuries."

But while the heart was long a fixture in the language of love, its emergence as an image of love did not come until much later, in the middle ages.

"The first visualization of the heart looks more like a pinecone or an eggplant or a pear," said Yalom.

Those first images appeared in the 12th century in illuminated manuscripts — the great picture books of the era, as Yalom called them. Some were secular, but most were religious. And that’s important, said Yalom. For just as the heart was emerging as a visual representation of romantic love, "there’s a parallel vein that is religious and thinks of the heart as the home of the soul," she explained.

Catholic holy card depicting the Sacred Heart of Jesus, circa 1880.
Auguste Martin collection, University of Dayton Libraries

But over the next century, the paths would diverge. Religious imagery — think of those sacred heart of Jesus paintings — retained that more "pear-shaped" heart. But as secular romance stories became more popular, romantic love came to be represented by a different heart — that simple, perfectly symmetrical, bilobed “heart shape” that we know today.

Yalom said that shape had certainly been seen before the middle ages. It appears on coins from ancient Libya, and on silver vases from 6th century Persia. But Yalom says in those days it was purely decorative — a pleasing line, just not symbolizing love.

"It was a shape in search of a meaning," she said. 

Why did it find it’s meaning in romantic love and lasted the test of time? Yalom has a theory. She believes it simply works as a symbol, touching us on an ethereal level.

"You have two half-hearts merging into one — that beautiful idea dear to Plato that each of us have a longing for our other half, for our soulmate," she said. "And that heart captures that longing."

And also, on another, more physical one.

"Perhaps on an unconscious level those two lobes to suggest breasts," Yalom said. "And buttocks. And speak to our more sensual natures."

That this symbol is the centerpiece of Valentine’s Day today makes total sense. What does not make nearly as much sense is why we celebrate romantic love on the feast day of a 3rd century Christian martyr. So, what’s up with that?

"Well, that’s one of the great mysteries," said Yalom. "There have been various theories as to why St. Valentine’s Day became consecrated as a day for lovers and none of those theories is really based in fact."

That the heart’s rise to prominence in religious and romantic spheres coincided perhaps offers a clue. That St. Valentine’s feast day comes on the cusp of spring — and mating season — is maybe another.

What we do know is that a holiday more closely resembling our modern Valentine’s Day began to emerge in France and England in the late 1300s. And, in 1415, the oldest confirmed “valentine” was sent from a French poet imprisoned in the tower of London.

"And what has been preserved is a letter or card that he wrote to his wife who had remained in France starting [with] 'Ma très douce valentine,' my very gentle valentine," explained Yalom. 

Given her expertise on the subject, I ended my chat with Yalom by asking why she thought a day set aside for romantic love has not just lasted, but thrived, across multiple cultures for more than 600 years?

"I think it speaks for the enduring power of romance," she said. "And even if we don’t believe that there is only one predestined heart for each of us, we still want to feel our hearts flutter."

I’m not sure even Sappho could have said it better herself.