First, an awful clickbait ad:

I’m not clicking through to play your stupid game. The smartest person in the world doesn’t have an IQ of 300.

Just looking at statistics of the bell curve, how high should we expect the numbers to go?

The smartest person in the world is probably Chinese. China is the most populous country in the world, with 1.38 billion people. With that many people, someone should be 6.05 standard deviations above the mean. China also has a higher average IQ than most countries, around 105. Add those together and the smartest person in China should have an IQ of 196.

But the smartest person might also be Jewish. Ashkenazi jews tend to score higher on intelligence tests than other groups, getting an average IQ around 115. There are only about 23 million Jewish people in the world and they’re not all Ashkenazim. Assuming they all have the same mean IQ, the most intelligent person should be 5.35 standard deviations above the mean, for an IQ of 195.

Despite being only 0.3% of the world’s population, Jewish people have won more than 25% of Nobel prizes in physics, medicine, and economics. The Manhattan project drew heavily on Jewish immigrants from Europe. Having a higher average IQ pays off heavily, when it comes to people at the high end of the distribution.

The smartest person in the world is probably a man. That’s not because men are smarter than women — both genders seem to be equally intelligent, on average. But there’s more variability among men, more men are outliers that are either very dumb or very smart. At an IQ of 140, men are overrepresented, 3 to 2. And the same at an IQ of 60.

There’s reason to think this difference is biological. This pattern is consistent in test scores across 40 different countries. The pattern shows up at a young age, perhaps as young as 3 years old. And variability is higher among males, in other traits, and in other species. This seems like a feature of evolution — evolution experiments more with males. Men compete, women pick the winners.

One estimate is that men have 14% higher variability in intelligence than women do. Adding that in, we might guess that the smartest man in China has an IQ somewhere around 202 and the smartest woman around 190.

Again, high variability also hurts some men on the low end of the curve. If there’s someone in China that’s 6.05 standard deviations above the mean, there should also be someone who’s that far below, with an IQ around 8.

I’m not sure what it would mean to be that dumb or how you’d test someone… I don’t think they’d be able to solve even the simplest of puzzles.

I suspect the entire concept of intelligence breaks down, below a certain point. The measured bell curve is not symmetrical, there’s an extra bump of people on the left side:

Theoretical bell curve (shaded), compared to measured bell curve. From Jensen 1969.

The bell curve is formed by adding a whole bunch of small positive and negative effects together. Some people have low intelligence because many random genes have added up to a low result. A person can also have low intelligence because they have one serious genetic flaw that harms them. This makes up that extra bump of individuals. You can tell the two groups apart by looking at their siblings — a person who is retarded by down’s syndrome or some other major mutation has siblings with average IQ’s. A person that is low IQ without any major mutation has siblings that are also low IQ.

The concept of intelligence also breaks down a bit at the high end. In general, a person that’s above average at math is also above average at reading and writing. When looking at the most extreme cases, though, this relationship breaks down a bit. The best mathematician in the world is not going to be the best writer in the world. The concept of single most talented person is flawed. To be the best at any one thing takes years of work and specialization. Either way, we’re probably looking at an upper limit on IQ somewhere around 200.

If we look up this question, we can find a lot of clickbait lists of famous smart people, trying to identify the smartest person in the world.

There’s some problems with the stats here. The lists often include children, and IQ is sometimes measured differently in children and adults. People get smarter with age, up until maybe their late teens. For younger children, you can just divide “mental age” by “actual age” to get IQ. This concept doesn’t really work above 15 years old.

Marilyn Vos Savant claims an IQ of 228, because she earned a 23 year old test score at 10. She was incredibly precocious, and scored pretty well (170–180's?) on tests as an adult, but it’s unlikely she’s the smartest person to ever live.

Terence Tao is one possible candidate for the world’s smartest man.

There’s probably some kid out there today who will be grow up to be smarter. As the world population increases, we should see a few more outliers: more exceptional athletes like Usain Bolt or Michael Phelps, and also more exceptionally gifted minds.

But the average population IQ is more important. To get one smartest person with an IQ ten points higher (from 202 to 212), we’d need a Chinese population of 100 billion or an Ashkenazi Jewish population of 1 billion. An IQ of 300 would still be so rare that we shouldn’t see it, even with a much larger population. To get to 300, we’d have to raise the world’s average IQ. Could we do that? And how high could it go?