This is the kind of thought that occurs to me when I can't sleep.

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If I recall correctly Sir Paul Nurse, who is a Nobel Prize laureate and the current President of the Royal Society, has a most unusual family. His biological mother became pregnant with him when she was quite young and unmarried. Consequently her parents raised him as their own and he grew up thinking of his mother as his older sister.

Most strangely, his biological grandmother too was the child of an unwed mother, and was raised by her grandparents thinking her biological mother was her older sister. The same was true of his biological grandfather, the man he thought of as his father.

Thus the women he once thought of as his mother's sister and his father's sister would have been his great grandmothers. The people he once thought of as his grandparents would have been four of his 16 actual great, great grandparents.

And you think your family tree is complicated.