Many responses (Molly's age, Hagrid, JKR stuff, unforgivables, etc) - also, Moody's Eye

[Zara]

No: HPFGUIDX 173909

> JKR Chat:
> "How exactly do muggleborns receive magical ability?
> JKR: Muggle-borns will have a witch or wizard somewhere on their 
family
> tree, in some cases many, many generations back. The gene re-
surfaces
> in some unexpected places."
> 
> Random832:
> Whoa. Kind of turns the whole "blood doesn't matter" message inside-
out. 
> Also means the department of mystery findings about muggleborns is 
going 
> to be harder to overturn (since while the conclusions about "theft" 
are 
> wrong, the basic findings are true rather than being something 
wholly 
> fabricated by Voldemort and Umbridge)
> 
> Also, how far back, exactly? All of humanity is descended from the 
same 
> person some 8,000 years ago (at the most conservative estimate - 
it's 
> considered more likely to be something like 3,000 years ago).

zgirnius:
I assume Rowling meant a few generations back, far enough to ensure 
that the family is no longer aware of the witch/wizard ancestor. 

A real-life analogy: One of my sisters is a blonde. The hair colors 
of our parents are brown. The among our grandparents, three had browm 
hair, one had flaming red hair. As my grandparents were all 
immigrants to the US from Europe, and moistly died before I was born 
anyway, I have never met my great-grandparents, and have no idea what 
color any of their hair was. But someone going back far enough, must 
have been blond, which is where my sister gets it from. Were she a 
witch, this would be exactly what Rowling is saying about 
Muggleborns. My parents both carry the genes for blond hair without 
expressing them, and as luck would have it, one of their three 
children inherited them from both. 

All this says is that just as there is no such thing as a true 
pureblood, there is no such thing as a true Muggleborn. A pureblood 
is a 'half-blood' whose pedigree may be traced for a number of 
generations and contains only witches and wizards; a Muggleborn is 
a 'half-blood' who is not aware that his/her ancestors included 
witches or wizards. A 'half-blood' is a witch or wizard who knows 
s/he has both Muggle and wizard ancestors.

This was what always made sense to me, anyway. I don't see how this 
in any way strenghtens the bloodist position - to me it illustrates 
its absurdity.