Are Leavers thicker than Remainers? The short answer is: yes. At least, on average. That's according to a paper analysing voters on both sides of the godawful Brexit referendum, which says that: 'When compared with Remain voters, Leave voters displayed significantly lower levels of numeracy, reasoning and appeared more reliant on impulsive ‘System 1’ thinking.'
Now obviously I voted Leave and I'm super-duper clever, but this is not remotely surprising; June 23 was effectively a vote on globalisation, which favours the more intelligent and educated at the expense of the less gifted. When rising sea levels turn our little ponds into great lakes, the big fish are going to benefit a great deal more. Globalism has also come to be seen as a high-status belief system, something Christopher Lasch foresaw in his prophetic The Revolt of the Elites, writing that the ruling class were escaping from their traditional ties and obligations towards the rest of society and becoming less rooted. Among high-status people - not necessarily on the Left - nationalism began to be seen as vulgar and proletarian.
The aristocracy have always been more international - the occasional French name among English toffs is a remnant of this - and mobility has always correlated with social status. In London in recent years we've had the phenomenon of postcode killings - teenage boys murdered by other teenage boys because they come from the wrong area. People at the very lowest social strata are extremely immobile and loyal to their area.
On top of this, it has been shown consistently that intelligence correlates with both economic and social liberalism. It's why previous studies in America showed about a three to four IQ point advantage among Republicans over Democrats; although I imagine that may have shrunk now, as Trump acquired more working-class voters at the expense of the college educated. There is also an association between lower intelligence and ethnocentrism, which makes sense for a number of reasons, one of which is that the more intelligent tend to exhibit greater trust towards a wider circle of people.
So if it's true that progressive ideas such as globalism are associated with higher intelligence, does that mean they are right? Not necessarily. Firstly, very clever, well-educated people have been fantastically wrong about things in the past, the prime example being Communism, which attracted some of the brightest minds in the West long after it was decent. The cult of diversity is another, likewise built on a utopian idea that natural human instincts like ethnocentrism can be eliminated, despite much evidence to the contrary. Those sort of utopian ideals, which look better theorised in academia than when actually implemented, tend to appeal to the more highly-educated; that's partly also because people tend to gravitate towards the belief system of their peers, and if everyone in your circle believes in X and hates Y, it's hard to resist.
Secondly, people tend to support the political ideas that favour them; if you're what David Goodhart calls an 'Anywhere' then it is very much in your interest to support free movement, which makes your life considerably better; if you're less competitive in the job market, and in particular lack the culturally-specific soft skills that insulate many people from overseas competition (as people in the media do) then you have good reason to be more sceptical. On top of this the former are more likely to have friends whose jobs and wellbeing depend on globalisation.
Thirdly, though, ideas that are popular and successful tend to overstretch; what we see on American campuses right now is a form of runaway liberalism, similar to the evolutionary concept, where the competition to be more faithful to the progressive creed encourages people to extremes; this in turn usually leads to a backlash, a corrective. With the issue of the global vs. local, there are obviously enormous benefits to globalisation - especially in trade and in areas like science - but there are also huge advantages to nationalism in its loosest sense, since nation-states are still the best method of achieving free, liberal and prosperous societies.
If social capital erodes so much that a country's institutions and political norms begin to crumble with it, the disadvantages of not being allowed free travel on the continent are going to seem pretty quaint in comparison; you only need to look at what's unfolding across the pond with their clannish, third-world president. So just because an idea is seen as low-status, that is not a good enough reason to ignore it, since it might have social benefits affecting us all. On the other hand, of course, I might be just a bit biased.