IQ and height

A recent study has confirmed what was already previously known: on average, IQ and height are positive correlated. It is important to emphasize that correlation does not imply causation, but rather that ceteris paribus, groups of tall people will likely have an average IQ which is higher than similar sized groups comprising shorter people. The study by the world class universities of Edinburgh and University College London analyzed data from thousands of Scottish families over a six year period. Unlike previous studies about IQ and height, the researchers analyzed DNA markers of over 6,800 unrelated people. The study concluded that 70% of the variation in IQ was genetic while the remainder was down to environmental factors.

IQ and height may be correlated but explanatory factors are still poorly understood. Plenty of theories have been put forward including that height may be a marker of good nutrition, maternal stress and overall general mental and physical health. Other possible explanations include that increased height may be associated with larger brain size, which could in fact explain the general association in fairly simple and logical terms.

OK, IQ and height are correlated. So what? Well the real life implication of higher IQ are well known. Prior studies have suggested that height at the age of 18 is a predictor of subsequent scholarly performance. And scholarly performance is related to graduated prospects and thus the ability to secure a better job. This may also provide an insight into previous studies that linked height to earnings potential throughout one’s lifetime. So as a group, you would expect taller people to do better relative to shorter people.

IQ and height: people are getting taller

The good new for the human race is that people are getting taller – a lot taller. Over the last 150 years, it is believed that the average height of humans has increased by nearly 10 cm (4 inches) in industrialized nations. If people have been getting taller, and if brain size has in fact been keeping pace with the overall increase in human height, this could potentially explain the Flynn effect, which states that people in industrialized nations have been increasing their IQ scores at a rate of 3 points per decade in the United States and up to 6.7 points per decade in places like the Netherlands. Interestingly, the Netherlands happens to be the industrialized nation with the highest average height for both men (6ft and 0.5 inches) and women (5 ft 7 inches). This again could help explain why the Dutch collectively have an average IQ which is higher than other industrialized nations. At, we have been keeping track of how well people from certain countries have been doing on our test. It so happens that two of the people with the highest IQs happened to be Dutch. It would be interesting to understand whether they also happened to be tall.

But being tall is not all good news. Taller people have also been shown to live shorter lives on average, are known to be more prone to back problems and large body sizes create a headwind for hearts pumping blood. This illustrates that you just can’t have it all.

If you are interested in testing your IQ, you can do so here.