Not daughters/dads or sons/moms but here in Ohio USA you can legally fuck your sister (or cousins, maybe auntie too, haven't checked) as long as she's AOC. Here's that's 16, and no age gap considerations either. So if a 16 yo girl wants to have her 30yo brother's baby she legally can (the reality is breeding risk is generally blown way out of proportion by moralist morons that don't know what they are talking about and probably also think the Earth is flat and 6,000 years old, it's about double the risk for 1st generation siblings, 4% vs. the general population's 2% risk of complications, I have 6 with my sis and they are all perfectly fine). Marriage is a bit more tricky and requires use of a loophole: you can't legally marry your family members (it will get annulled when eventually Columbus becomes aware of it), but like most other US states automatically recognizes legal marriages from other states and countries. And it just turns out that in Argentina siblings can legally marry, so just requires a bit of planning and a trip to Buenos Aires. As far as the rest of the world most still won;t allow marriage but some like Argentina don't care:
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Adding them all together = over half the human race can legally fuck their family if they want to, the ~2% of the other half probably just keeps it in the closet like the LGBT's did/do in the places where that was or still is illegal.