Why is southern Italy poorer than northern Italy?

Anyone who wants to understand southern Italy should read "Il Gattopardo" (The Leopard) by one of the last peers of Sicily.

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.

This phenomenon isn’t confined to Italy. You see it across Europe, the US, and (reversed) in Australia. Charitably, you could chalk it up to sunnier regions being better for agriculture and not cities, but I think that heat simply causes the human brain to thermally throttle, which makes humans in hotter climates slower (and dumber). And less enterprising, and wealthy. And certainly humans need to be more resourceful to survive in areas with less food available. Is it a coincidence that the last uncontacted tribes are all in the equatorial belt? Coelacanths of the modern world!

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.

So you're saying it's a bad thing that the US has spent most of my lifetime squandering its social capital?