To tell twins apart, look at their…
…belly buttons! Navels are scars from the detachment of the umbilical cord after birth, so they aren’t caused by genetics. Another way to determine who’s who: take fingerprints. Identical twins may share DNA, but exposure to different areas of the womb during development affects the fingertips’ ridges and whorls.
Twins can be conceived by two different fathers
Heteropaternal superfecundation occurs when a woman has sex with more than one man during ovulation. Sperm from each man fertilises an egg, resulting in twins. Though this phenomenon is common in dogs and cats, it’s extremely rare in humans.
The chance of having twins is much higher than it was 30 years ago
The birthrate for twins has increased 76% since 1980, an uptick that some experts attribute to older women having children (women in their thirties are more likely than women in their twenties to have twins). Or maybe women are getting taller: A Long Island Jewish Medical Center study found that women who birth twins or other multiples were, on average, more than an inch taller than women who only birthed one child at a time.