[uoaei]

I've always had the suspicion this was partly the case.

If you're born in August or September when the sun is out for a long time and everyone's jovially enjoying social events during the first few months of your life, of course you'll be more outgoing and positive and active!

[executesorder66]

If that were true there would be a 50/50 split between extroverts/introverts. (Or shy/outgoing, however you want to define it)

But there are statistically more extroverts than introverts, so this is empirically wrong.

[svnt]

It could be right, if the equatorial regions are above the extrovert threshold.