One in Every 50 Births: Why the World Has More Twins Than Ever

This year, about 1.6 million pairs of twins will be born. That's 3.2 million people arriving with a built-in companion, a genetic mirror, and (if you believe any twin I've ever met) someone to blame for everything.

That number is not normal. It is, according to researchers at Oxford, higher than at any point in recorded human history. And it keeps climbing.

The global twinning rate right now sits at about 12 twin deliveries per 1,000 births. Back in the early 1980s, that number was 9.1. A jump of roughly a third in less than 40 years. In demographic terms, that is a huge shift. We don't change how humans reproduce this fast.

So what happened? And why does one small town in Nigeria have so many twins that locals have basically given up trying to explain it?

The Rate Actually Changed. Here's Why.

There are two types of twins. Identical (one fertilized egg splits in two) and fraternal (two separate eggs get fertilized at the same time). The identical twin rate is pretty much fixed. About 3 to 4 per 1,000 births, no matter where you are on Earth or what century it is. Nobody knows exactly why an embryo splits. It just happens, roughly at the same rate, everywhere.

Fraternal twins are a different story. Their rate varies wildly across populations and time periods. And that is the rate that's been rising.

Two main things drove the increase. First: fertility treatments. IVF and other forms of assisted reproduction often involve transferring multiple embryos to improve the odds of success. More embryos, more chances of two sticking around. The US twin birth rate went from about 18.9 per 1,000 in 1980 to 30.7 per 1,000 in 2023, according to the CDC. That's a 60% jump in four decades. Fertility clinics did a lot of that work.

Second: older mothers. Women who have children later in life (their 30s and 40s) naturally produce higher levels of follicle-stimulating hormone, which can cause the ovaries to release more than one egg at a time. This is just biology. And since women in wealthy countries have been having children later for decades, you'd expect fraternal twin rates to go up. They did.

The Town That Can't Stop Having Twins

There is a town in southwestern Nigeria called Igbo-Ora. They call it "the twin capital of the world," which sounds like a tourism slogan someone made up, but the data backs it up completely.

The Yoruba people of West Africa have the highest naturally occurring twin birth rate on the planet. According to data cited by Wikipedia and confirmed across multiple research papers, the rate among the Yoruba sits at roughly 45 to 50 twin sets per 1,000 live births. That is four to five times the global average. Walk down a street in Igbo-Ora and you will meet more twins than you've probably seen in your entire life.

Why? Nobody is entirely sure, which is the honest answer. The most popular theory involves yams. Yes, yams. The specific variety of cassava-like tuber eaten heavily across the Yoruba diet is thought to contain natural phytoestrogens that might stimulate the ovaries to release multiple eggs at once. A 1978 study by Nigerian researcher P.P.S. Nylander first floated the idea. Science has been cautiously interested ever since but hasn't conclusively proven it.

Could be the yams. Could be genetics. Could be a combination of things we haven't fully mapped yet. But whatever is causing it, the effect is real and it's been consistent for generations.

Identical Twins Are Random. Fraternal Twins Run in Families.

Here's a thing a lot of people don't realize. If you're an identical twin, that's basically a fluke. It doesn't run in families. There's no "twin gene" for identical pairs that gets passed down. Your mom being an identical twin does not increase your odds at all.

But fraternal twins absolutely run in families. The tendency to release multiple eggs in a single cycle is heritable. If your mom is a fraternal twin, or if she has fraternal twins in her family, your odds go up. The gene does the rounds.

And here's something that might mess with your head a little. Identical twins don't have identical fingerprints. Their DNA is a match but their fingerprints form based on the specific position each fetus sits in the womb during development, which is always slightly different. So even two people sharing every base pair of genetic code are still, down to the fingertip, distinct individuals.

That's actually kind of beautiful if you're into that kind of thing.

Twins Through History (It Gets Weird)

Humans have been fascinated by twins forever. Romulus and Remus (the mythological founders of Rome) were twins. Jacob and Esau in the Bible were twins who supposedly wrestled inside the womb, which is either a metaphor or a story someone told to explain a difficult pregnancy. The Aztec god Quetzalcoatl had a twin named Xolotl, the dog god. Greeks had Castor and Pollux, the Gemini, up in the stars.

Not everyone thought twins were a good omen, though. Several historical cultures believed two babies at once meant the mother had been unfaithful, which is not how biology works but logic was not always a priority. Some communities in West Africa historically viewed twins as sacred. Others feared them. The Yoruba, interestingly, developed a detailed spiritual tradition around twins precisely because they had so many of them.

The modern English term "Siamese twins" comes from Chang and Eng Bunker, conjoined twins born in Siam (present-day Thailand) in 1811. They toured with P.T. Barnum, settled in North Carolina, married sisters, and fathered a combined 21 children. Their story is genuinely one of the more extraordinary in 19th century American history, and almost nobody knows it.

Chang and Eng died in 1874, within hours of each other, which at this point feels like a fittingly dramatic end to a dramatically unusual life.

Why Counting Twins Matters More Than You Think

Here's the thing about twins and census data. They mess with it. Not intentionally. Just by existing.

Historically, twins had higher infant mortality than singletons, which means earlier census counts systematically undercounted them. In many countries, birth registration systems were slow or unreliable, and a twin birth might only be recorded once. Or the second twin might be recorded days later with different data. Or not at all.

This sounds like a small technical problem. It isn't. If you're studying child health outcomes, or tracking population growth, or trying to understand fertility patterns across a population, miscounting twins distorts your entire picture.

Today, data from the Oxford study covering 165 countries and 99% of the global population gives us the best global snapshot ever assembled. 1.6 million twin pairs a year. Every single one of them a separate, distinct human being who deserves their own count.

That's the thing about twins that gets lost in all the statistics and the mythology and the yam theories. Each person is their own person. Two separate humans with separate fingerprints, separate lives, separate numbers.

Which is, come to think of it, the whole point of counting everyone.