Basically, though Owl remembered it backwards - Northeners from colder climates (Germanic tribes, Nords, Scots, etc) are in order to compensate for that more hot in body and thereby more passionate and quick to anger, with somewhat overheated brains but very strong bodies - great warriors and laborers, but poor in intellectual pursuits on average.

It was the opposite for people from Warmer climates, their bodies were 'colder' and their brains worked much better but their bodies were weak - great intellectuals and artists, poor warriors and laborers.

The Romans and Greeks, of course, being in the middle of these two poles had the best of both worlds. Or so the thinking went. It's also worth noting the Romans didn't see this as hereditary, exactly - it was thought that people moving to different temperature areas would cause them to have the same characteristics as the locals within just a few generations.