As I’ve said before intelligence is not that straightforward. We used to think IQ was about 50% inherited and then recognised the impact of upbringing which started the nature-nurture debate.
Geneticists discovered that your genes could also be influenced by environmental factors – epigenetics – but also that people who were assumed to have inherited certain skills probably got them through hard work.
Other recent research show that high IQ scores are as a result of innate intelligence PLUS motivation (See posts on intelligence). That means you can improve your scores if you really want to.
It is clear now that there is no single gene for intelligence and the latest research at the University of Edinburgh shows that about 40% of the variation in knowledge (crystalline type intelligence) and about 50% of differences in problem-solving skills (fluid type intelligence) are due to genetic factors.
Scientists still can’t tell you exactly which genes have an effect on intelligence but have found broad patterns. Research like this could help to understand how people suffer cognitive decline in old age (See: Can you keep Alzheimer’s at Bay?).