Newsweek asks:

Why Do IQ Scores Vary By Nation?

Global differences in intelligence is a sensitive topic, long fraught with controversy and still tinged by the disgraceful taint of pseudosciences such as craniometry that strove to prove the white ”race” as the most clever of them all. But recent data, perplexingly, has indeed shown cognitive ability to be higher in some countries than in others....

Using data on national ”disease burdens” (life years lost due to infectious diseases) and average intelligence scores, the authors found a striking inverse correlation–around 67 percent. The countries with the lowest average IQ scores–Equatorial Guinea, Cameroon, Mozambique, Gabon–have among the highest disease burdens. In contrast, nations with low disease burdens top the IQ list, with Singapore, South Korea, China, Japan, and Italy in the lead.

There's no question that hookworm and many other diseases sap mental energy. But Singapore is as close to the equator and as low in altitude as those African countries, so its inherent disease burden potential is about as bad.

Sociologist Robert K. Merton coined the term the Matthew Effect from the Gospel:

"For to all those who have, more will be given, and they will have an abundance; but from those who have nothing, even what they have will be taken away."

But the passive voice here is misleading. The Singaporeans, under the guidance of their supersmart control freak leader Lee Kwan Yew, weren't given a low disease burden, they earned it. They worked very hard to improve hygiene and health. What would be a more important use for spare IQ points than to fight disease?