Growing up in a chaotic home may be bad for children's minds, a study suggests.
Children from organised homes performed better
Researchers studied nearly 8,000 twins born in Britain between 1994 and 1996. Some were identical, others were not.
London's Institute of Psychiatry found those living in noisy, disorganised and cramped homes were less intelligent, New Scientist magazine reported.
Since the children were twins, the researchers were able to establish that this was caused by their environment and not their genes.
Other studies have come up with similar findings. However, it has not been clear until now whether genetics or environment is the biggest factor.
Researchers were able to tease out the answer because the children were a mixture of identical and fraternal twins.
This meant that some of the children had exactly the same set of genes while others shared only half their genes.
The study found that the homes of wealthier and better-educated parents were slightly more organised. Their children were also slightly more intelligent.
However, when they took genes out of the equation they found that household chaos had a significant impact on intelligence.
Those living in organised homes were more intelligent than those living in chaotic homes.
"It just makes sense," said Professor Robert Plomin, the lead researcher.
"If a kid is in a really chaotic home, it's hard to imagine that they can learn in a normal way.
"Their surroundings just aren't subtle enough for them to tease apart the world."