Both my own paternal line (originally from Scotland) and my paternal grandmother's paternal line (originally from Denmark, and perhaps from England before that) belong to haplogroup R1b. The two lineages, however, belong to two different major subclades: I am P312, while my paternal grandmother's paternal line is U106 (the same as my friend). These subclades both descend from an older R1b lineage called L11.
The huge spread of L11 and its subclades within Europe can be traced back to a man who lived in the Bronze Age and who might have been a chieftain, according to one study (some comments and criticism can be found here). The study estimates the man to have lived around 2000 BC. I think of him as my ancestor, of course, but he is also the direct paternal ancestor of around half of all Western European biological males. If we count all lines of descent (not just the direct male-to-male lines), this man is, without a shadow of doubt, an ancestor of every European alive today and of unknown millions of non-Europeans as well.
Whether or not this man was a chieftain, there currently seems to be general agreement among scientists that he probably belonged to a culture that spoke the proto-Indo-European language or a very close descendant of it (probably a dialect that later split into the Celtic and/or Italic languages).
The mainstream view is that the proto-Indo-European language and culture originated in the Eurasian Steppe, straddling the border between Eastern Europe and Central Asia. With the help of horses (which may in fact have been first domesticated by them - or perhaps not), the proto-Indo-Europeans spread out in every direction, eventually reaching as far as Western Europe, Northern India and the Tarim Basin in modern-day China. They brought with them Y-DNA haplogroups R1a and R1b, two branches of the ancient haplogroup R1. While both R1a and R1b are associated with proto-Indo-European language and culture, it is in fact R1a that is most obviously correlated with Indo-European languages in its distribution, and it is still present at high frequencies in the original Indo-European steppe homeland.
In addition to identifying Indo-European Y-DNA lines, there have also been efforts to identify autosomal admixture originating in the proto-Indo-Europeans. One such effort is FTDNA's ancientOrigins tool, which breaks down one's European ancestry into three ancient categories, including one called "Metal Age Invader", identified as the autosomal signature of Indo-European-speakers who also brought with them haplogroup R1b and perhaps even the gene for lactose tolerance. Below is a screenshot of my ancientOrigins result. As you can see, I am 14% "Metal Age Invader", which is a normal amount for a Norwegian.
However, GenePlaza's calculator K14 Ancient Cultures has me as 40% "Eurasian Steppe", so FTDNA's 14% estimate might actually be too low.
The languageThe most lasting legacy of the proto-Indo-Europeans, apart from their genes, is their language. The proto-Indo-European language is the origin of many of the world's major languages, including all the Germanic, Romance, Celtic and Indo-Aryan languages as well as Greek and several extinct languages (such as Hittite, the earliest attested Indo-European language). Proto-Indo-European (usually shortened to PIE) has been largely reconstructed, and several texts have been written in it. Some people have even made recordings and YouTube videos of themselves reading these texts aloud, giving us a glimpse of what the language of these ancient ancestors of ours actually sounded like:
https://www.youtube.com/watch?v=H6b3_8bswfM (Schleicher's fable; read more about it here)
The proto-Indo-European language also featured prominently in the 2012 movie Prometheus.
Listening to readings of reconstructed proto-Indo-European, I find that the language sounds familiar to my ears. I can hear resemblances to many of its daughter languages, such as Lithuanian, Russian, Greek, Hindi, Persian, German and even Old Norse, the forerunner of my own native language, Norwegian. Hearing these ancient voices, as it were, is touching on a personal level; I imagine the proto-Indo-Europeans in their windswept villages, speaking to each other in this strange-yet-familiar tongue, and I can't help but wonder how similar and different their way of life would have been to the traditional Norwegian culture I know so well. What would it be like to go back in time to meet those people?
Ever since the common origin of the Indo-European languages was discovered by linguists, many (including the Nazis) have tried to leverage Indo-European identity for racist purposes. This is an insult to the proto-Indo-Europeans themselves, but most importantly, it is an extremely ill-founded endeavour. The Indo-European genetic, cultural and linguistic heritage ties hundreds of millions of people together across geographic, religious, ethnic and "racial" lines. Europe certainly does not have an exclusive claim to this identity.
And of course, we must not forget that the ancient proto-Indo-Europeans were culturally and genetically mixed just like we are today.