The average adult IQ is actually lower than you might think!

So, what factors might influence whether a person has an average IQ as an adult, or an IQ below or above this average?

Well, lots! And many are most influential during childhood. A study found that environmental factors such as place of residence, the physical activity of a child, the family income, and parental education level have an important impact on the IQ of the children (Makharia, 2016).

But genetics also plays a key role in determining whether an adult has an average IQ. Studies of identical twins have found a correlation between intelligence and genetics, with identical twins IQ scores more similar than those of fraternal twins. This shows that siblings with a more similar genetic makeup are more likely to report similar IQ scores, and thus cement the notion of genetic factors in IQ. Other studies have found that siblings raised together in the same environment had more similar IQ scores than adopted children raised alongisde them, suggesting that although all children shared a similar environment, genetic similarities between siblings meant there was a greater correlation between their IQ scores.

But as well as environmental and genetic factors, biological factors influencing foetal development can also have an impact on whether a child grows up to have an average IQ as an adult. These include exposure to drugs and harmful substances in the womb, the age of the mother, and whether the baby received all the necessary nutrients in the womb, or suffered from prenatal malnutrition.