Rituals around coming-of-age, first menstruation etc. also seem to oppose your claim. Plus also: common sense (have sex, pregnancy bump appears, baby comes out). The ability to deduce is common to all humans. If you think that indigenous Australians lack this faculty, that's kind of amazing.
So just happenstance?
> Modern humans spent about 200k years without figuring it out as well
Say that were true, your amazement in your OP would be a little strange.
> The sex-pregnancy link was figured out by observing domestic animals, a luxury they didn't have
I'll point you back to the sibling comment as evidence to the contrary:
https://news.ycombinator.com/item?id=37972080
Rituals around coming-of-age, first menstruation etc. also seem to oppose your claim. Plus also: common sense (have sex, pregnancy bump appears, baby comes out). The ability to deduce is common to all humans. If you think that indigenous Australians lack this faculty, that's kind of amazing.