Re: Define "Aryans"
Well, I lack a better term than "Aryans". Let me define it for you as I understand the term. For me, "Aryan" would be a people of indo-european descent whose meets the following criteria:
1) Mostly stayed in Europe/Middle East after the Indian/European split
2) Did not do much in the way of mixing with the mongols when they were a-invading
3) Did not do much in the way of mixing with the moors when they were a-invading
4) No mixing with East or South Asian peoples after about 10,000 BCE
5) No mixing pretty much at any point with Polynesians or Aborigine peoples
That doesn't leave a hell of a lot of people. Celts/Gauls (Hallstatt and La Tène) pre-moor invasion would seem to qualify as they would have been the most isolated Indo-European peoples.
Germanic tribes and Nordic countries are probably a safe bet. Slavic nations I'm a little unsure about, as their populations saw a lot of mixing with mongolians not too far back. Alexander the Great also did a rather good job of muddying the waters on this, what with sewing his seed to and fro.
More scientifically, it's a neat way of packaging up populations dominated by Y haplogroups R1a, R1b I1, I2a, I2b, N1c, N1b, and N1c without much in the way of genetic influence from the surrounding Y haplogroups Cx, Ex, Fx, Gx, and Jx. (The other haplogroups, to my knowledge, never really having "bordered" the "Aryans" so the genetic mixing being even less frequent and likely.)
Right up until the end of the neolithic gene flow didn't seem to happen that fast. Humans were still speciating. natural selection was still "a thing". Since the end of the neolithic we seem to have mostly stopped evolving gross phenotypic variations due to hybridisation. Genetic variance seems to be largely down to mutation and selection-by-disease. (As opposed to climate, scarcity, etc.)
Some of that is probably down to "the neolithic wasn't all that long go", so populations that defined the end of that era remained mostly relevant. Some of that, however, really is down to increased gene flow since then. We got better at moving around the world. We spread our genes.
Unfortunately, we don't really have good terms for a lot of these end-neolithic populations. Relying on haplogroups is inaccurate, as neither mtDNA or Y-chromosome groups accurate reflect population grouping (and the associated genetic isolation). Similarly, using cultural or linguistic terms (such as indo-european or indo-iranian) is equally inaccurate.
For example, the closest mtDNA groups are R, I and W-descendant populations, but these don't neatly overlap with Y haplogroups R1a, R1b I1, I2a, I2b, N1c, N1b, and N1c. if you researching both groups however, you start to get a rough idea of the populations in question and the genetic trait clustering in question.
Despite this, modern humans did experience a period of relative genetic stagnation some time between Y chromosome Adam and Babylon. It created distinct populations each with their own genetic clusterings.
Most interestingly, while individuals that are part of the population I was discussing as "Aryan" are more likely to have lactose tolerance than non-Aryans, it really can't be used to define the population as the evolution of lactose tolerance was only about 6000 years ago. That's well after the neolithic and into the point where we started roaming around the earth a lot more frequently.
That said, Lactose tolerance as well as the "resistance to the plague/HIV" genes would help you narrow things a little, as both of those are far more likely to occur amongst the "Aryan" populations. (Though many "Aryans" would not have them, and our gene spread has brought them to other groups."
Speciation and taxonomy are imprecise.
Use of the term "Aryan" is thus not an attempt at sparking any hatred, but simply a lack of anything more precise. It is the most accurate term I know of to represent the specific population (and associated cluster of genetic traits) that I was thinking of in my previous comment. Alternative (less angry-making) terminology suggestions are welcomed.