Two weeks ago I posed the following query:

"I have heard it stated that in some countries overrun by the Nazis, that
local populations were required to prove their lack of Jewish ancestry by
producing their own family trees. Is this just a myth or is it true and if
so, which countries were affected? Regarding Germany, I don't think this
was the case but perhaps it might have been in some areas? All ideas
welcome on this issue!"

There were so many useful responses which I have summarised in case others
might find the information equally helpful:

In short, it was not a myth that the non-Jewish population had to prove
non-Jewish ancestry. In fact, it was in many instances a matter of survival
as well as an opening for promotion within the ranks of the SS and the
Gestapo and the opportunity to get a job in the public service or join a
university. >from 1935 it was also needed by those who wanted to get married.

The evidence took the form of either a document or a family tree showing
Aryan ancestry which then had to be verified by the Nazis, some were stamped
with a swastika. Some (e.g. those wanting to
join the SS) had to research their ancestry back into the 18th Century, no
mean feat in pre-computer days! Many who wrote to me stated that they had
been informed of the practice by non-Jewish friends, descendants of those
who had to produce this documentation. This practice was not confined to
Germany but my respondents also reported that the practice was also known in
France, Italy, Holland and Austria. The inference could be drawn that
enforcing people to produce proof of Aryan ancestry was probably commonplace
in all the countries invaded by the Nazi regime.

I was also sent this link which giving more detail, I found most useful:
https://en.wikipedia.org/wiki/Aryan_certificate

A big "thank you" to everyone for their help.

Diana (Mohr) Gomes da Costa, Kent UK - formerly >from London -
Researcher number: 166938 email: dianadacosta@btinternet.com

Researches include ARNSTEIN, BACH, BASS, BERLIN, COHN, DITTMANN, FLACHFELD,
GUETERMANN, HAHN, HELLMANN, HIRSCHMANN, KOHN, KRAILSHEIMER, KUGLER, LOEWI,
MANES, MARX, MENDEL, MORGENTHAU, MOHR, ROSENFELD, ROSENWALD, UHLMANN,
WEIKERSHEIMER and ZIRNDORFER - all originally >from Bavaria, mainly Furth,
Nurnberg and Bamberg as listed in the JGFF database.