There's no clear-cut answer. Marxists will tell you that in early agricultural societies, the strongest who were tasked with defending the settlement in exchange for food were the first to obtain status and wealth off the fruits of other's labor. Proto-capitalist-aristocracy, if you will.

More recent discussions point to the fact that very early agricultural societies tended to get dominated and become subservient to those societies which did not become sedentary; the non-sedentary dominators then became the aristocracy.

What's certain is that there have always been "haves" and "have-nots" in human society.

What's left of the modern european "Nobility" like to draw elaborate family trees, and generally point to either Charlemagne or an illustrious Roman as the final great ancestor. How accurate these family trees are can only be judged on a case-by-case basis (and the answer is often, "Not Very").

As an example, the Visconti, lords of Milan from the 13th to the 15th century (and active in Lombard communal politics since the 10th century) claim to have been landholders in Massino on the shores of lake Garda since the land was granted to an ancestor in the days of Imperial Rome. Today, although the main Visconti line died out in the 15th century, a cadet branch continues to live in a modest villa near Bologna. I went into more detail here, where I also gave some other tidbits on old Italian families.

Another example in the answer linked above are the the Obertenghi, who descend from Boniface, a Bavarian ennobled with significant lands in Northern Italy by Charlemagne. To this day there are Milanese and Emilian (based in the town of Zibellio) branches still in existence, both are active real estate developers in the Emilia-Romagna region.

I also gave a similar answer here in a thread that then completely digressed, and here, where I elaborate that Roman descent was also popular among non-dynastic families, especially in the Republic of Venice. Dandolo family, for example, traces their lineage back to the Roman gens Ursia, specifically from Orso Ipato and his son Teodado Ipato, who were Byzantine Military officers when the Northeastern Italian lagoons were a Byzantine protectorate.

The Badoer family of Venice also traces their origins to the Gens Ursia, and in the early tenth century there is indeed record of one Ursus Badovarius applying for a subsidy when raving Maygar hordes devastated his land somewhere near Altino at the edge of the northern lagoon. That area between the mouth of the river Sile in the northern lagoon and the fortified town of Eraclea was one of the primary settlement areas for Byzantine soldiers, so I suppose the claim is realistic, but really we're taking the Badoer on their word here. The examples among Venetian families go on; were the Contarini descended from the Roman Aureli Cotta as they claim? We don't know, the first we hear of them is a jurist in the early ninth century underwriting a will. And the Giustiniani trace their heritage to Emperor Justinian! We have spotty documentation of a Byzantine family called Giustiniani in Istria that arrives in Venice sometime before the eleventh century, but that's it.