It's easier to point to young children as an example. The second link, for example, includes:
> I have a child who could not poo if someone was in the room or he was being watched, so a soon as he could move for privacy, he did. ... Many other kids will at least need to avert their eyes and at least pretend they have some semblance of privacy. Others will let go while grinning at you.
FWIW, my 3-year-old son loves to watch me poop, and will run into the bathroom when I need to go. And I let him, and don't find it difficult to poop.
I do have a hard time getting a sense for how much is "rooted in genetics" beyond the simple fact that we are living creatures.
Some people are scared of flying. Others are not. This cannot be a direct result of genetic selection, for obvious reasons.
Some children love certain foods, while a sibling does not. This too cannot be explained by simple genetics.
So given examples like the Romans, and Chinese and (again from the second link) "About a billion people -- 15% of the world's population -- practise open defecation" and "In the Samoan house there are no walls... the beaches are used openly as latrines." - how meaningful is it to say it's 'rooted in genetics', any more than we can say that at some level English is rooted in genetics?