Twins have fascinated people for thousands of years, appearing in myths, literature and science. National Twin Day, on December 18, celebrates twins, triplets and other multiples, along with the families who raise them. Whether you're a twin, have twins in your family, or simply find the science of twins interesting, it's a fun day to celebrate a unique bond. Many twins mark the day by dressing alike, sharing childhood photos, or simply spending time together.
History of National Twin Day
Twins have been part of human stories since ancient times. In Roman legend, the twins Romulus and Remus founded Rome, and Greek and Hindu mythologies include famous twin figures. In astrology, Gemini is represented by twins.
The science of twins developed much later. There are two main types. Identical, or monozygotic, twins develop from one fertilized egg that splits into two embryos, so they share nearly all of their genes. Fraternal, or dizygotic, twins develop from two separate eggs fertilized by different sperm, so they're as genetically similar as any siblings.
Scientists have long studied twins to understand how genes and environment shape traits, a method made famous by twin studies in the 20th century. In the United States, twin birth rates rose significantly from the 1980s through the 2010s, partly due to fertility treatments and older average maternal age.
The town of Twinsburg, Ohio, hosts an annual Twins Days festival each August that draws thousands of twins. The origin of National Twin Day on December 18 isn't well documented.
Why National Twin Day Matters
Twins share a special experience of growing up together from the very start. Celebrating them honors that bond as well as their individuality.
Twin research has also contributed enormously to science, helping researchers understand everything from heart disease to personality.
How to Celebrate National Twin Day
- Dress alike: twins can coordinate outfits for a day of fun.
- Share photos: post childhood photos side by side.
- Celebrate individuality: recognize each twin's unique interests and talents.
- Learn the science: read about identical vs. fraternal twins.
- Connect with twin communities: find a local multiples club or support group.
Celebrating at Work, School and Home
At work, twin colleagues might enjoy a playful 'twinning' theme day where coworkers coordinate outfits with a friend. In classrooms, the day is a great introduction to genetics: students can learn how identical and fraternal twins form, explore inherited traits like eye color, and discuss why identical twins still have different fingerprints. Literature classes can look at twins in stories and myths. At home, families with twins can make a photo collage of the twins growing up, interview them about their favorite memories together, or let each twin choose a separate activity to celebrate their individuality. Parents of young twins might connect with a local multiples support group.
Fun Facts About National Twin Day
- Identical twins come from one fertilized egg that splits.
- Fraternal twins come from two separate eggs.
- Twinsburg, Ohio, hosts a large twins festival every August.
National Twin Day FAQs
When is National Twin Day?
National Twin Day is December 18.
What's the difference between identical and fraternal twins?
Identical twins come from one egg that splits; fraternal twins come from two separate eggs.
Do identical twins have the same fingerprints?
No. Their fingerprints differ because of small variations in development in the womb.
Is there a twins festival?
Yes. Twinsburg, Ohio, hosts Twins Days each August.