Two Lots Of Identical Twins Separated At Birth, Raised As Brothers

Each set of brothers thought they were non-identical twins.

It's one of the world's more unbelievable stories -- two sets of identical twins were born at the same time in a Colombian hospital and somehow, one brother from each pair was swapped.

They each grew up each thinking they were non-identical twins, resigning their different appearances and natures to quirks of genetics.

While William Cañas Velasco and Wilber Cañas Velasco lived in the country, Carlos Alberto Bernal Castro and Jorge Enrique Bernal Castro were in the city.

Their worlds collided when a woman in a butcher's shop recognised her colleague from an engineering firm working behind the bench.

But he didn't smile and wave back at her, and was told 'that's not Jorge, it's William'.

The serendipitous story struck a cord with people around the world -- that these four would find themselves reunited as adults -- but for population scientist Jeff Craig, this story represented a once-in-a-lifetime research opportunity.

"It's one of life's most amazing accidental experiments," the Murdoch Childrens Research Institute associate professor told The Huffington Post Australia.

"It's a unique opportunity to look at nature and nurture -- how your environment affects the way your genes are expressed."

You really wonder when it comes to country vs city, are people healthier one way or the other? Jeff Craig

Craig researched how life in the country and city influenced the way their genes were expressed for a research paper that showed one set of twins had a different genetic profile.

"You really wonder when it comes to country vs city, are people healthier one way or the other?

"Studies show more exposure to nature protects from allergies, but then there's heightened exposure to pesticides and UV radiation."

The results showed that one set of twins' genetic profile was remarkably similar while the other had quite a few variations. As for whether those changes were visible to the naked eye -- ie more freckles or different allergies -- Craig said he wanted to know the answer to that himself.

"In short I don't know but I'm certainly interested. I looked at the epigenetic changes which tells you how a gene was expressed.

"These twins represent a phenomenal research opportunity.

"It's a funny paying to the old adage that all babies look alike."