you're right, we know very little about light pigmentation
but I don't agree with your asumption it originated in northern Europe
Tochars and the Tarim mummies where light pigmented too, this can't have originated in northern Europe
there are hints of light-pigmented Gutians who invaded Mesopotamia after the fall of the empire of Sargon the Great
where these Gutians came from is not exactly known, but it might be the Armenian highlands or south of the Caspian Sea
on the other hand, light pigmentation in Europe seems to be linked with haplo I1 and R, which is in favour of your asumption
but since I1 has been discovered in neolithic Hungary, I1 pigmentation could have been affected by EEF admixture[/QUOT
perhaps I was not clear enough: I thinK lightER pigmentation occurred in a region BETWEEN NORTH-EAST EUROPE AND THE eastern STEPPES, NOT IN NORTH-EAST EUROPE, not by force...
By the way, the fairest pigmented population are clearly NOT the Slavic nor Baltic ones! (and Estonians aren't baltic) - I cannot link this depigmantation with an unique culture as, say, the Indo-Europeans - and it 's not more linked to Finns or Ugrians - I think in a population speaking a language unkown to me, maybe a mix of western mesolithical H-G-ers (great weight to 'cromagnoids') with more "refined" but yet robust types, around central-northern Russia, having already developped one or more mutated gene IGNORED by today geneticians studies, OR having acquired it there, in East, from ??? I think Indo-Europeans (not all of their tribes but a great number) had a some (LATE?)stage a big proportion of this mix, more on the second element, so they carried this light pigmentation with them but I don't make a principe of a primary all depigmented I-Ean people... No "religion war" with me -
the principal skin depigmentation mutation common among ALL CAUCASIANS (Arabs comprised and N-Indians) cannot explain the today repartition of pigmentation in Europe, and the asiatic one is absent apparentlyin Europe - for i red, the genes of depigmentation beared by neanderthal have not been passed to us - on this last point somebody can correct me if I'm wrong -
&: Tocharians are supposed to be come from a more western place than their remnants say to us.
&: Gutians were said to be "light" that don't tell us HOW MUCH LIGHT they were in fact - Corsicans are not too light but in a very southern country of Arabia they would qualifed by "light" at some degree...
just my point