Not only do identical twins get double the wardrobe, twice as much fun at their teachers' expense and a best friend from birth, researchers have discovered they also live longer than singletons.
Researchers from the University of Washington have examined what being a twin means for life expectancy, and found that they have lower mortality rates throughout their lifetimes.
Furthermore, the study, which was published in the journal PLOS ONE, found that identical twins have a higher life expectancy than fraternal twins.
"We find that at nearly every age, identical twins survive at higher proportions than fraternal twins, and fraternal twins are a little higher than the general population," the study's lead author David Sharrow, a statistician and postdoctoral researcher in aquatic and fishery sciences, told Science Daily.
The study looked at 2,932 pairs of same-sex twins from the Danish Twin Registry, one of the oldest twin registries in the world, who survived past the age of 10 and lived in Denmark between 1870 and 1900 (and so had a complete lifespan).
They then compared their ages at death with data for the overall Danish population.
For men, the peak benefit of having a twin came when they were in their mid-40s. That difference is about 6 percentage points, which means that if out of 100 boys in the general population, 84 were still alive at age 45, then for twins that number was 90.
For women, the peak mortality advantage came in their early 60s, with a difference of about 10 percentage points.
The authors of the study believe the reason twins live longer may be because of the social support they provide each other, and the psychological and health benefits that come with that social connection.
"There is benefit to having someone who is socially close to you who is looking out for you," Sharrow said.
"They may provide material or emotional support that lead to better longevity outcomes."
Sharrow also suggests that identical twins may have a longer life expectancy than fraternal twins because of a stronger social bond.
"There is some evidence that identical twins are actually closer than fraternal twins," Sharrow said. "If they're even more similar, they may be better able to predict the needs of their twin and care for them."
If the findings can be replicated, Sharrow believes they have implications beyond twins to the wider population.
"Research shows that these kinds of social interactions, or social bonds, are important in lots of settings," Sharrow said.
"Most people may not have a twin, but as a society we may choose to invest in social bonds as a way to promote health and longevity."