A few centuries ago it was believed that the reason why people near the tropics didn't achieve the level of affluence of their northern conspecifics was that the heat made the blood grow thicker, and that slowed down their movements, and thoughts (thoughts at that time used to take place not only in the head, but also in the heart).
It's a funny theory, very catchy, as mechanistic as the time demanded and all that. No wonder it was appreciated for a while.
Many centuries have passed now, and we have a lot of better hypotheses for why there is less development in tropical areas than elsewhere. Here are a few.
More diseases that consume family resources
Lower average IQ
Centuries of exploitation by Europe and US
Fewer Institutions (There is a terrible paper by Daron Acemoglu, whom I hear otherwise is a great economist, on that)
Shorter east-west axis within a land area (Guns, Germs and Steel)
More frequent natural disasters, in particular floods, leading to property damage.
Probably all of those play a small role. I just want to say that primitive as it is as an explanation, I still think that the heat, and sunshine that comes with it, is a very strong factor, still today. Development is not my target though, my target is individual productivity and individual freedom, here thought of as "amount of things per unit time someone could be doing", not political freedom.
So far I've spent three weeks in England, at the Future of Humanity Institute in Oxford, this month. During those 21 days, I have experienced strictly 08 (eight) minutes of sunlight. Outside it is freezing. So no wonder that all interactions I had were had inside walls. Meanwhile talking to friends back home, at the Tropic of Capricorn, they had outside parties, picnics at the park, bike riding days, shopping outside in the streets, free dancing at the streets festivals, learning to do slacklining, swimming pool etc...
In this grey lowlight world of English weather, with the added factor that by and large interaction between anglophones is mostly linguistic, it is not admirable that many come to office even on Saturdays and Sundays, and also stay late during weekdays. Basically, where else would they go?
The same distinction I saw while in California when comparing it to Boston. Both I saw in the winter-ish. In Boston you can basically choose in which venue you will eat, and in which venue you will read. In California you could go to the park, or to the mountains, or hike in the woods, or walk through the beach, or even go to a theme park, or that weird place where people surf false waves...
Brains are devices you can train. If you train them to skateboard, or play with dogs, or play soccer in a park, that is what they will learn. If a brain is compelled to think all day long, and read, speak, listen and write, that is what it will get good at.
The cold constrains, and a lot, what people do on a daily basis, and thus they become more specialized, and better, in the things they do. I think that this plays an enormous role on why tropical people don't tend to intellectual/high productivity lives as much as people in colder regions.
A few more subtle considerations: There are human drives relating to outside activity that not even the cold can stop. But it can still significantly hinder. Groups of young people still summon the strength to face the cold in particular for two activities: Training for sport competitions, and staying in line for a dancing club. Curiously, those are ritualized forms of hunting and courtship, something that our most northern relative, the Japanese Macaque, finds worthy of leaving hot baths to do. You'll find Japanese Macaques walking around in the snow for the same reasons you'll find someone walking around in the snow in many of the coldest cities, and that is saying something. Kids in both species also play outside heated areas. Playing, finding food (or defeating rowing arc-rivals), and doing some sort of ritualized courtship are sufficiently worthy, for us and them,to face the spiking thorns of the cold.
The cold transforms sport into just sport. Get there quick, enter, play, leave. Whichever surrounding rituals could have arisen around sport, either they are left for the summer time, or they will perish culturally.
Same with the nightclub lines. No one will stay more than one second longer than necessary outside, they become only lines, strictly lines, and mini-skirted women pay in pain the price of wanting to be attractive/sensual. Men do also wearing fewer coats. No extra time before or after the party. And the only kind of making up that is allowed outside is the really drunk kind, since no one whose peripheral nervous system is sending the right signals to their brain would tolerate that cold, the same peripheral nervous system that should be delivering ecstatic feelings of seduction and desire.
Young people pay quite a price for the cold. But it's nowhere near the price that older people pay. In an Arabic country, there is a disproportion of males in the streets, and a western eye will frequently think that this is prejudice, or something bad, happening against women. Boston and Oxford are university towns, but even accounting for that, the absence of people at the 40-80 age group in the streets is shocking. In Buenos Aires, 23:00 on a Tuesday, you'll see hundreds of people, of many ages, strolling around the streets, chatting, having dinner, drinking beer, laughing etc... same for Rio, or São Paulo. Some people face the cold at older ages in Oxford and Boston, but not so many, they could get a cold after all, and they are mostly done with sport and nightclubs. There are more women walking around in Syria, than 50 year olds walking around in Oxford.
Lightlevels are also higher in inside areas than outside areas, as far as I recall, both in Boston and in Oxford, though not in California, Florida or the Latin cities cited. One more reason to stay inside.
My claim is then that life is more productive in the cold because the cold significantly constrains what people do, and it constrains it in the way that makes them produce for longer periods output of linguistic sort -including maths and programming and everything that is mostly parsing, coding, transforming symbols etc... - I'd further claim that this effect cannot be accounted for by the six factors mentioned above, and that it will at least be comparable in intensity with whichever one ends up being the strongest one among those.
A further claim is that because life in cold areas is significantly constrained, moving to colder areas is a costly signal of willingness to do lots of work. This could partially explain why most of the top 20 universities in the world are in very cold areas. You must really love studying if you are willing to constrain your life that much, and conversely, once your life is constrained, you'd better love studying.
Speaking of love, stats famously show that people in California are not happier than people in New England. Julia Galef famously disagrees. I don't know if the effect is neutral if you compare people born in one place who moved to the other. Like her, I'd bet highly it isn't. Sure after a long period there is a regression towards base level happiness, but I'll bet the regression is slow and incomplete, and the process takes very long.
I've spent about six months of my life in cold areas, partly travelling, partly working/researching. Despite all the costs that it entails, at this moment my inclination is to decide to live in one of those cold lowlight areas for a while. Get some work done, or some more work done, of a research kind, now that movement building already took some 2 years of me. I wrote this partly to better understand the trade-offs, to more clearly think about this decision. I hope it helps someone else who is thinking about similar, or opposite, decisions, I've met at least one person here, and one back in the US who were thinking of doing the reverse.
No wonder I'm writing from Oxford...