Christopher Langan has an IQ that falls somewhere between 190 and 210, a score so high it denies accurate measurement. A score so high it trumps Einstein. He also has an unusually enormous head, sixth standard deviations above the average human head size, according to his own calculations.

In an interview with “The Smartest Man in the World,” as he’s otherwise known, Langan briefly proposes a hypothesis that head size likely correlates with intelligence (though he does preface this with the age-old adage: correlation is not causation). He goes on to provide several examples in which smaller creatures (a centipede, for example) lack the capacity to achieve true intelligence, while relatively larger creatures (a common house cat) are markedly more advanced in their behaviors. 

Though Langan’s throwaway comments don’t necessarily deserve this level of scrutiny, I find his hypothesis interesting enough to examine further. His alternative hypothesis is this:

H₁: Organisms with larger heads have a greater intelligence.  

And his null hypothesis is this:

H₀: Organisms with larger heads do not have a greater intelligence.

There is no instance in which an experimental study could be carried out in this area, at least not with our current level of technology. Hypothetically, a scientist would have to submit a primate to several basic tests, chart the speed/efficiency with which it accomplishes said tests, then surgically/medicinally enlarge its head. The same primate would be submitted to the same tests, and its speed/efficiency would once again be recorded. Results that indicate significant improvement would strongly suggest a causal relationship between head size and intelligence; however, a single test would not constitute solid evidence, and more primates would have to undergo testing.

A correlational study, while lacking an experimental study’s tangibility/reliability, is a more realistic method to use when investigating the ‘head-size/intelligence’ link. In Langan’s interview, around the 40-second mark, he offers centipedes and housecats as examples supporting his theory. He then goes on to list monkeys, and then humans. Each organism is more intelligent than the last. However, if we follow this head-size/intelligence relationship to its logical conclusion, the hypothesis begins to fall apart.

Sharks are not smarter than humans.

Elephants are not smarter than humans.

Whales are not smarter than humans.

Though the aforementioned animals have larger heads than that of an average human being, they are not on our plane of intelligence, as we define the word. Knowing this, we must reject the alternative hypothesis (H₁), and accept the null (H₀). Organisms with larger heads do not necessarily have a greater intelligence.  

A question meriting legitimate studies might look like this: is intelligence affected by brain size? Do organisms with larger brains have a greater intelligence? But that’s a blog post for another day.