5 Misconceptions About Twins

Identical twins form when a single egg is fertilized by one sperm and the resulting embryo splits into two. Fraternal twins, meanwhile, occur when two eggs are released at the same time during ovulation and are fertilized by different sperm. Both outcomes result in two babies being born at least roughly around the same time.

Twins, and particularly identical ones, have long been the subject of research, speculation, and fascination. Along the way, a lot of misconceptions about this unique sibling dyad have emerged.

1. Misconception: Twins are always best friends
2. Misconception: Studies have shown that twins can be telepathic
3. Misconception: There is “good” twin and one “bad” twin
4. Misconception: Identical twins all have exactly the same DNA
5. Misconception: Identical twins run in families
6. Misconception: Twins always share a birthday

Misconception: Twins are always best friends

Many twins are indeed close, brought together by the unique experience of being raised at the same time and place, of looking exactly alike, or both. Of course, not all twins share a bond. 

Some twins simply don’t get along from the start. Others are close as kids but struggle to individuate as they grow and attempt to define themselves outside of their sibling relationship. Twins can sometimes simply be nothing alike, and twin relationships can be just as fraught as any other familial connection.

Studies have found that identical twins do tend to share more friends than fraternal twins, and often start out with similar personality traits. However, these twins often grow more different as they age. Though connections are common between twins, there are always exceptions and outliers, and even identical twins can simply be completely different.

Misconception: Studies have shown that twins can be telepathic

The internet is full of stories about twins who claim to be able to read each other’s thoughts and even feel each other’s pain, and the idea of telepathy between twins has long been a topic of speculation.

Some preliminary studies have identified events that could be interpreted as signs of telepathy, such as a 2013 study in which identical twins were exposed to loud noises, and one out of four pairs displayed a reaction that was “above chance.” However, this research is still relatively scant, and ultimately, as of today, “there is no credible scientific evidence that twin telepathy exists,” psychologist Tania Johnson told National Geographic. 

Instead, she said, what might appear to be telepathy could actually be the result of two people who were raised the same way and developed extremely similar ways of responding, making choices, and seeing the world. Near-identical genetics could also play a role in linking identical twins, particularly in cases of twins who were raised apart.

Still, it may not be time to rule out telepathy quite yet. “Scientists must still remain open-minded to events that may someday prove there is twin telepathy,” Nancy Segal, director of the Twin Studies Center at California State University, told National Geographic. “But that day seems far in the future—if it arrives at all.”

Misconception: There is “good” twin and one “bad” twin

The concept of an “evil twin” dates back to ancient mythology. It appears in Zoroastrian cosmology, which tells of twin spirits named Ahura Mazda (Ormuzd) and Angra Mainyu (Ahriman). These spirits are often thought to symbolize good and evil, though they actually represent the duality of existence. Many other ancient faiths also have stories about the world being created from a battle between twin-like spirits connected to good and evil.

Over the years, the idea of an “evil twin” has become a common storytelling trope found across many genres. In some stories, the protagonist’s “evil twin” might resemble them in appearance but may have a slightly different characteristic, such as a scar or an eyepatch. This double may symbolize memory, corruption, or something else the protagonist wants to escape. 

However, in all these paradigms, the idea of the “evil twin” seems to represent the existence of evil or darkness within the self or in the world, rather than having anything to do with actual twins. In the case of real-life twins, the truth is that there simply is no “good” or “bad” one. Instead, real-life twins are more likely to have various dualities within themselves, just like everyone else. 

Misconception: Identical twins all have exactly the same DNA

Identical twins develop from the same zygote, so it was long believed that they had the exact same DNA—but this is actually not the case. These types of twins do tend to be very similar genetically, but some pairs are much more different from each other than others. 

A 2021 study found that 15 percent of identical twins had one twin whose genetics had mutated significantly. Another study found that among 381 identical twins, only 38 had no identifiable genetic mutations distinguishing them. Genetic differences in identical twins arise from mutations that can occur before or after embryos split.

Misconception: Identical twins run in families

There is actually no established evidence that identical twins can run in families. However, the tendency to have fraternal twins can be passed down genetically. Additionally, the likelihood of having twins increases with age, according to UT Southwestern Medical Center. A previous twin pregnancy can also increase the odds of another one by five times. 

Misconception: Twins always share a birthday

Twins don’t always have to be born the same day or even the same year. As long as a mother is pregnant with both babies at the same time, they’re classified as twins. 

Labor can be a long and complicated process, and it can take days, weeks, or even months for the second baby to emerge. The longest interval ever recorded between twins' births was 90 days; this occurred in 1996 when a mother gave birth to one baby prematurely, and doctors stopped her contractions and kept the second child in the womb.