Yamnaya genetics

I've long thought that there was some political motivation behind the obvious glee in the "haha, Yamnaya people had dark hair and dark eyes and darker skin than is common to northern Europe today; suck it white people!"  This was especially challenging when it became obvious that the Yamnaya were the biggest single core of today's European population, including areas that turned out to be have among the highest concentrations of blond and red hair and blue eyes on the planet.  Even the area in which the Yamnaya culture flourished has blond hair and blue eyes in genetic studies on the next wave of burials of the cultures that immediately followed the Yamnaya (and which were descended from them) and cultures as far away (today) from a "Nordic" physical type as Greece and Rome talked about the original patrician and aristocratic classes has having "flashing" eyes and blond and red hair in an area where it's today almost completely absent.

In other words, it never made much sense to me that the Yamnaya were a different physical type than what their immediate descendants obviously were.

However, the Eupedia article that I just found sheds some light on the question.  Let me quote a portion:

What did Yamnayans look like physically? 

According Kurts (1984, p.90), people of the Yamna culture consisted of three distinct phenotypes corresponding to the relatively recent blend between three populations. The dominant type was tall, dolichocephalic, with broad faces of medium height. The second type was more robust with high and wide Proto-Europoid faces. The third type was more gracile, with narrow and high faces of the East Mediterranean type. 

The average height for Yamnayan men was 175.5cm (5 ft 9 in), approximately the same as the modern average for American and French men, and slightly taller than the average Mesolithic EHG men, who stood at 173.2 cm. 

Yamnayan DNA tested by Haak (2015), Wilde (2014), Mathieson (2015) showed that Yamna people (or at least the few elite samples concerned) had predominantly brown eyes, dark hair, and had a skin colour that was moderately light, lighter than Mesolithic Europeans, but somewhat darker than that of the modern North Europeans. This is not unexpected considering that these samples had about 25% of recent admixture from the Iranian Plateau (before the Indo-European migrations brought Northeast European genes to the region), which would have darkened their pigmentation. Other tests have confirmed that the vast majority of Mesolithic Europeans had blue eyes, and the high incidence of red hair among Northwest Europeans (who have the highest percentage of Yamna ancestry) as well as in the Volga-Ural region and in ancient Chinese depictions of the Tocharians from the Tarim Basin strongly suggest that red hair was found among Yamnayans, and that the genes for red hair (which also include some mutations for fair hair) were spread by R1b Indo-Europeans. (=> see The Origins of Red Hair) 

The high CHG admixture in elite Kurgan samples was not found in earlier Steppe cultures, apart from a single R1b sample from the Khvalynsk culture that differed from non-R1b samples in that regard. This indicates that a foreign intrusion from the South Caucasus is responsible for this unusually elevated CHG among the Yamna elite. The considerably lower CHG admixture observed in German Bell Beaker and Unetice samples (average 10%), whih represent the advance of R1b tribes into Central Europe, hints that the rest of the Yamna population had higher Mesolithic European and lower Caucasian ancestry than the Yamna samples tested to date, and could consequently have looked more like modern Scottish and Irish people. This would mean mixed blue and brown eyes, and mixed hair colours with brown hair being predominant, but with a sizeable minority of red hair and perhaps also blond hair. Blond hair appears to have originated among Mesolithic Northeast Europeans, and is therefore be more common in populations with high levels of (Baltic, Slavic and Germanic) R1a.

That... makes a lot of sense.  Some poor sampling because of social causes of who gets buried in the kurgans and who doesn't, and probable over-abundance of Maikop genetics in the ruling caste of the Yamnaya means that they may have actually been a bit darker than was normal for the region.  This CHG (Caucasian Hunter Gatherers; the ancient population group that probably is the root of the Maikop civilization which was a vector for metallurgy and heirarchical kurgan burials into the steppe region) infusion into the territory of the Dneiper-Donets, Khvalynsk and Sredny Stog territory had probably been going on for some time, but it probably ultimately resulted in the evolution of those cultures into the Yamnaya horizon as well.  That higher incidence of CHG genetics was eventually diluted in the successor populations, which also spread over northern and central Europe, picking up (among other things) genetics from substrate WHG (Western European Hunter Gatherers, which actually peaks in East-Central Europe in the Baltic region among Estonians and Lithuanians) who were, at least in a large part of their area, proto-Uralic peoples linguistically.  That is, related to today's Finns and Estonians and Lapplanders, etc.

In Northern and Central Europe, the already mostly light-eyed and ruddy-haired Yamnya people superimposed themselves socially over a thin substrate that was also blond, light-eyed, etc. and they did so in sufficient numbers that the Corded Ware horizon is mostly Yamnaya genetically.  These two suites of physical features were sufficiently similar that they amplified each other to a great extent, creating the population of northern Europe today.  The spread into central Asia, Chinese Turkestan and southern Siberia had very little admixture at all, because the region was essentially unpopulated, hence the fact that Afanasievo genetics is identical to Yamnaya genetics.  Until it reached far enough to eventually reach Mongoloid phenotypes and the Europoid and Mongoloid phenotypes mixed to create, for example, the green-eyed and red-haired Genghis Khan many millennia later, not to mention Chinese descriptions of the Wu-sun barbarians as having red hair, green eyes and "looking like monkeys."

Farther south in Greece, the Italian and Iberian peninsulas, Anatolia, and the spread into the Iranian plateau and as far (eventually) as India the Europoid phenotype was eventually genetically swamped to a great degree by the larger populations of darker "Mediterranean" phenotypes, but not without leaving its mark on the upper caste for millennia, as well as the original physical types appearing in written records for many, many centuries after the superimposition over the locals.

The more things change, the more they stay the same.  All of these theories fell out of favor three quarters of a century or so ago—they had been commonplace throughout academia prior to that.  Now, genetics is proving them right all over again.  That's what you get for putting political and social concerns over empirical concerns, though—your science is led predictably astray.