Australian scientists on Saturday said they discovered genes are responsible for 40 percent of our lifetime intelligence with the other 60 percent being determined by our environment.

The research was carried out by scientists of University of Queensland of Australia and was led by geneticist Professor Peter Visscher.

The environment a child grows up in (nutrition, schooling, parent's education) impacts on intelligence, but observational tests on twins suggested that we inherit around half of our intelligence.

But until now, there has been little understanding of the genetic contribution to cognitive aging, or how smart we stay as we get older.

According to Visscher, the more intelligent you are the longer you live, the more healthy you are, and the higher your income is later in life. So it is no wonder there is so much interest in understanding what determines intelligence.

Visscher and colleagues studied a unique group of nearly 2000 unrelated people in Scotland who were tested for their intelligence, using the same test, at age 11 and again at age 65, 70 or 79 years.

Most people who began life with above average intelligence were above average when they were older, while others who had below average intelligence tended to stay below average.

However, the researchers did note that there were some whose intelligence improved and some whose got worse, relative to others.

They also took genetic samples and quantified the role genes play in determining how much change there is in intelligence as we age.

"We estimate roughly a quarter to a third of that change is genetic," Visscher said in a statement.

"Measuring detailed environmental factors over a person's entire life course is very difficult."

In conclusion, environment contributes more than genes to determining intelligence, however, both play an important role.

Visscher said it was a lot easier to study genes while it was important to study the environmental determinants of intelligence.

He claimed that genetic studies of larger samples in the future could help identify specific genes involved in mental aging, which could also help in understanding the biology of Alzheimer's.

Vietnamnet