The findings contradict the claims of those who insist that intelligence is inherited genetically or even racially and fixed for life. The three French researchers studied the IQ of 65 children before and after they were adopted between the ages of four and six.
Before adoption, they lived in negligent or abusive families. Their IQ was found to be 85 or less (average intelligence is 100). After living with caring families for between five and 10 years, their IQ had increased appreciably.
Children adopted into loving but relatively poor families increased in IQ by an average of 8 points. Those adopted into better-off families improved by an average of 19 points.
Michel Duyme, a member of the French research team, said: "It's now up to educationalists to make practical use of our findings."