Oh yes it's a very fascinating subject which I only got into about a year or so ago because of a throwaway remark made by my friend about people with rhesus negative blood being descended from aliens, she not knowing I was rhesus negative myself.
I hadn't given it a thought before then since having my children 40 odd years ago.
A rhesus negative mother whose partner is rhesus positive will reject the antibodies of her children in the womb, no other species apparently does this, which is quite odd in and of itself. Only since the 1960's when it was trialled (in Liverpool??) was an injection given to mothers in this circumstance so as not to reject future births. Usually the first birth is OK but it is subsequent births that are rejected.
