[not a specific family question but a general opinion on families overall type question: do you find it odd the some species have 'only children' or wonder how some people manage with having no siblings at all?]
I do. At least I do from a social standpoint. I can understand why quarians are usually only children, for instance, but humans?
I wonder who they talk to when they're growing up. It's not like they have a dozen uncles or aunts, or cousins living with them. Some of them only have their parents. Do they forge stronger friendships outside of the family?
In the end, clan system has its drawbacks. But I wouldn't trade in my siblings to become an only child. Even the ones who drove me insane growing up. Off-planet it also has its advantages. If your car breaks down on Illium you can go into the databases and call up someone from your second circle who lives nearby and usually they feel obligated to help.
Being an only child sounds like a lonely existence. No one knows you like a brother or sister does.
