"Race," Politics

I realize this is chiefly a linguistic forum. I'm sorry for posting
on tangentially related topics, but like some people here I am
interested in population genetics *purely for tracing migration
routes* like the person who posted earlier --- NOT because I have
some racist agenda. People are people are people, wherever you go.
I posted on Pearson because I am unfamiliar with him -- not sure
that I want to be now.

Anyway, I will try to confine myself to linguistic questions from
now on. My first one is has anyone published a good grammar of
reconstructed PIE? The reason I joined this list in the first place
is because I was curious about the PIE genitive. I was discussing
the Greek genitive in another forum and started wondering about
genitive singular terminations in -s v/. the masculine/neuter -ou ,
which is the only one that doesn't have an -s ending. Did the 2nd.
declension masc. originally have an s too? I think I once read that
PIE supposedly had only two genders. I suppose some of the masc.
and fem. forms were distributed into the neuter, which would explain
why neuters have both types of endings. But how did the -s ending
make it to some masculine genitive singulars? Was it there all
along in all genders or was this a Greek innovation. If so, what
caused it?