when is close, too close?

[Gumleaf]

my question is, how close of relations can you be before it causes you a problem with dating and stuff. now i'm not talking about myself here, joanne and i are not related in any way that we know of, but i'm talking about a cousin here and this is how it came up. this week my cousins fiance's great grandmother died. i'm sure its sad for him and his family, but thats nothing unusal in the grand scheme of things. but the thing is, the great grandmother is also an aunty of my cousins father. i don't want to even begin to try and work out how they would be related, but is that too close in your opinion? for me at first i thought ewww, but when you think about it, if the relatives are that distant in their case, the chances are that others are in the same situation and maybe don't even know it. so i think its fine, what do you think?

[Zephyr]

Okay, let me work this problem out on paper...

They'd be like 4th or 5th cousins, your cousin and their finace.
It seems like it would be close,
But in reality their common ancestor would be like many generations back,
So the gene pool is diluted enough that it really wouldn't matter.

I believe as long as it's 3rd cousins or more,
Then it's perfectly safe.
That's what I learned in CP Bio anyway.