Not sure about the malaria cause, but it is true that the South of Italy has traditionally been far less free and far more dependent on agriculture than the north. It has a history of being conquered over and over again by different foreign powers which led many times to extractive regimes (and inevitably less innovation - some parallels to the American south before the abolition of slavery). Such an environment led to them invent something even worse than a disfunctioning state, namely the mafia.

Until reunification in the 1860s Italy had a bunch of city-states in the North, tight fisted control by the Church in center Italy, and an extractive / agriculturally dominant economy in the south ruled by the aristocracy.

I can see the last point improving over time. I give absolutely 0% chances to the first two points changing over time, bar some apocalypse-level destruction and rebuilding of society.

Long shot - but I wonder if climate also plays a part, as in the development of Singapore: https://www.vox.com/2015/3/23/8278085/singapore-lee-kuan-yew...

"Sicilians are horny and lazy, it's not complicated, I'm not reading this."

He now works in banking. Much to think about.

It felt like visiting a third world country.

My guess is that it is primarily a culture issue.

More speculatively, Europeans in particular could have been subject to extreme selection pressure during ice ages. Glaciers made it all the way to central Italy, which would have definitely shaped the evolution of humans, both biologically and socially, in those areas.

Finally, humans are less fertile at higher ambient air temperatures, and the risk of death greater than in milder climates. A population boom spurs all kinds of cultural and evolutionary and epigenetic changes.