Washington: It`s known that intelligence is mostly inherited. But, whether a person can become a clever grandma or grandpa relies on both genes and environment, says a new study.
Past studies of the genetics of intelligence have been performed on twins or siblings adopted and raised in different environments. Although the studies showed a genetic component of intelligence, they weren`t able to determine how this changes over a lifetime.
But, the latest study by researchers at the University of Edinburgh in the UK found that both the genes and environment affect how a person`s intelligence changes as they age.
"Until now, we have not had an estimate of how much genetic differences affect how people`s intelligence changes across the lifetime," lead researcher Ian Deary was quoted as saying by LiveScience.
"These new results mean that researchers can seek both environmental and genetic contributions to successful cognitive ageing," he said.
For their study, published in the journal Nature, the team studied a group of 1,940 Scottish people whose intelligence was measured when they were 11 years old. They
were tracked down recently and had their intelligence measured again at an age that ranged between 65 and 79 years.
The researchers also collected genomic data from blood samples and studied whether having similar genes impacted a person`s cognitive abilities at age 11 and later in life.
The researchers didn`t identify the specific snippets of DNA involved in intelligence, but they were able to determine how much of a role having the "right" genes -- whatever they
are -- plays in lifelong intelligence.
It was found that intelligence -- as measured through IQ tests -- itself is highly in heritable and can be passed down from parent to child. They also found that it comes from not one gene, but from small effects of many genes, and these same genes affect intelligence in both youth and old age.
On the other hand, whether this intelligence changes over time, they found, is very reliant on the environment.
"These results suggest that genes contribute to our understanding of why some people`s brains have aged better than others, but the environment is probably the larger influence on lifetime changes," Deary said.
"The results also suggest that many of the same genetic factors contribute to intelligence differences in childhood and old age."
According to the researchers, about 25 per cent of these intelligence changes over time were due to genes, while the rest came from the environment.
These genes that are involved in cognitive change could be related to diseases like dementia, they said.
Deary said: "Clues to the origins of people`s differences in cognitive decline could be useful for understanding more about dementia.
"We are planning to look closely at brain structure with our older people to see if there are links between genes, brain structure and cognitive skills in old age."
Environment also had an impact on intelligence stability; the intelligence of some improved while others declined. This could be influenced by such things as how active an older person is, the researchers concluded.