For a group that makes up just 0.4 percent of the world’s population, identical twins have enthralled moviegoers.

"A mom-to-be thinks she’s expecting twins—until the doctor spots something incredible during the ultrasound. What they ...

Twins—smaller at birth, on average, than singletons—start out smaller in pregnancy than was previously known, according to a study by researchers at the National Institutes of Health (NIH). The ...

Are we seeing double? Prince Archie and August Brooksbank couldn't be more similar in the most adorable family photos. Royal fans have previously noted their similarities with their beautiful ...

The trans-Neptunian object Altjira, 44 times farther from the Sun than Earth is, could be the second known trinary, ...

Rachel was shocked when she learned she would be welcoming quadruplets. Speaking to ABC News, the mom of six recalled being ...

Identical twins, or monozygotic twins, share the same genetic material, which explains their physical similarity. However, they show differences in behavior and personality due to several factors.