Is this proof that intelligence is 'set' the day we're born? Identical twins separated at birth have near-identical IQs, fascinating study from the world's leading expert in twins reveals

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Identical Chinese twins separated at birth by the nation's draconian one-child policy grew up to have almost identical IQs, a fascinating study reveals.

The research, led by Dr Nancy Segal an expert in psychology from the University of California, considered one of the world's leading experts on twins, examined the intelligence scores of 15 pairs of identical twins adopted by different families.

Fourteen pairs of twins were female due to Chinese culture traditionally favouring male children, a bias which led to female children, including twins, being abandoned by parents during China's one-child policy which ran from 1980 to 2016.

These genetically identical twins were separated and raised in different environments — and sometimes even in different countries.

This provided scientists with the rare opportunity to test if nature or nurture was the most important factor for IQ.

Research, led by Dr Nancy Segal an expert in psychology from the University of California and considered one of the world's leading experts on twins, examined the IQs of 15 pairs of identical twins adopted by different families

Dr Segal is considered a leading authority on twins and has found separated twins growing up in totally different families, sometimes even totally different cultures can have remarkable similarities. Here Dr Segal (centre) is pictured with Ann Hunt and Elizabeth Hamel

The twins underwent IQ tests twice, once when they were, on average, 11-years-old and then again, after some years had passed, when they had an average age of 14.

Comparing the results between the twin pairs over time the researchers discovered their scores were nearly identical.

Publishing their results in the journal Personality and Individual Differences, the authors wrote: 'Despite their different homes, educational experiences, and (in some cases) residences in different countries, the twins appear to have interacted with their environments in ways that aligned with their genetic propensities.

'This supports the notion that environments do not act randomly in fashioning developmental outcomes — rather, individuals behave selectively and actively with respect to the people, places and events that engage and challenge them.'

Dr Segal said that the older twins got the more their IQ scores seemed to align in the long term.

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'As genetic factors kick in, the environment drops out. So they become more alike with time,' she told The Times.

She based this finding off another aspect of the study which examined data from nine pairs of Danish identical twins who underwent similar IQ tests as adults.

While the data on this group of twins was more limited that the Chinese cohort, it similarly showed that twin pairs tended to match each other for changes in IQ between the two tests.

Concluding their study the authors said the results suggest that 'twins can be expected to achieve similar results on school tests, whereas unrelated siblings can be expected to achieve different outcomes.'

They continued: 'Knowing this will help parents and educators tailor their treatment, resource provision, and expectations of different children within families.

'In doing so, they may avoid the frustration that may come from encouraging and/or expecting outcomes and goals that may be outside the child's inclinations.'

Dr Segal and the other authors acknowledged an obvious limitation of their study is the overall small number of participants, a somewhat unavoidable factor given the rarity of identical twins being separated at birth.

As such they say the results should be interpreted with caution.

Dr Segal added: 'Should parents and educators throw their hands up in despair? 

'Absolutely not. Everybody can become smarter. But we’re not going to all be the same.'

While the latest study suggested separated twins has similar IQs some case examples have shown the opposite.

Dr Segal has previously reported the remarkable case of two identical Korean twins separated in 1976, one raised in South Korea the other in the US after they went missing.

Tracked down 40 years later, they showed remarkably similar personality traits but differed when it came to IQ with the American twin 16 points behind her genetically identical sibling.

It bears mentioning the American twin had suffered three concussions in life that her South Korean counterpart hadn't, and this may have influenced the results.

Measuring IQ and equating it to 'intelligence' in real life has proved controversial.

For example, some experts highlight that people can score highly on IQ tests which measure logic, abstract reasoning, learning ability and memory, but struggle to apply these day to day.

Identical twins are those born from the same fertilized eggs which then splits into two genetical identical embryos.

They differ from non-identical twins which happen when two separate eggs are released and then fertilised at the same time.

Identical twins have been linked to various have been linked to various shared behaviours before.

Some studies have found twins are likely to share nail biting habits, and reports have emerged that some twins share cancer symptoms even if only one of them is suffering the disease.

Perhaps the most starting twin stories come from pairs who were separated at birth but share remarkedly similar lives.

Some studies have found twins are likely to share nail biting habits, and reports have emerged that some twins share cancer symptoms even if only one of them is suffering the disease. Picture posed by models.

One of the most famous examples of this are the 'Jim twins' Jim Lewis and Jim Springer who were separated at birth.

Dr Segal, who has written about their case, said that despite being raised in different environments the pair both suffered tension headaches, bit their fingernails, smoked the same cigarette brand, both enjoyed woodworking, and even vacationed on the same Florida beach.

The leading expert on twins also worked with another pair separated at birth Ann Hunt and Elizabeth Hamel who were only reunited at the age of 78.

Ann from Aldershot, Hampshire, didn’t even know she had a sibling until her daughter Samantha Stacey discovered Elizabeth while tracing their family tree.  

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Whereas Elizabeth always knew she had a twin but had given up hope of ever finding her, and had moved to Portland, Oregon, USA.

They have earned a place in the Guinness Book Of World Records as the longest time apart for reunited twins after their emotional reunion in Los Angeles, California.

The girls were born out of wedlock in 1936 in Aldershot and their mother Alice Patience Lamb couldn’t cope and both were to be adopted.

But domestic servant Alice couldn’t find anyone to adopt Elizabeth, because she had a curvature of the spine so only gave Ann up. 

When the pair finally made contact, they both learned they had married men named Jim.   

Dr Segal who funded their trip to be reunited said at the time: 'Fascinating work on separated twins shows that here are twins growing up in totally different families, sometimes even totally different cultures, and yet they bring with them similar types of attitudes - in politics, religion, social behaviour.

'Where do these things come from? It’s difficult to know exactly but it seems that their genes linked to intelligence, personality and temperament just lead them to have similar types of world views.'